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Exam #3 (Chapters 9-12) Concepts you should know
Go through practice exam questions using the Study area of Mastering Biology, review quizzes.
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Chapter 9
What is Cell Division?
Cells divide up to create new cells via either mitosis or meiosis
How does a multicellular organism go from a single cell to a multicellular being?
Mitosis through cell differentiation
Cell differentiation - the process by which cells change in structure and become capable of
carrying specialized functions
What are Sister Chromatids, what is a Centromere, Chromatin, and a Genome?
Sister chromatids – Identical copies of each other is that formed by the replication of a
chromosome, that is joined together by a centromere
Centromere - Area where the chromatids of a chromosome are attached
Chromatin - entire complex of DNA and proteins that is the building material of chromosomes
Genome - all of an organism's genetic material
What is the Cell Cycle?
It is ordered series of events that a cell undergoes as it grows and divides into two daughter cells.
Found in all living organisms
What is Mitosis – Somatic Cells, where are these cell found? How much actual DNA is
found after mitosis occurs?
Asexual reproduction.
Somatic cells are all the body cells except for gametes, 23 chromosomes per set.
It is a type of cell division in by which a single cell divides into two genetically identical
daughter cells. It is important for the growth, repair, and replacement of tissues in multicellular
organisms
Since it is a copy of a itself. BOTH of the daughter cells have the same amount of DNA as the
parent cell. The chromosome are now 2 identical sister chromatids.
What are the Phases of the Cell Cycle? How do they occur? How long does it phase tend
to last? The entire cell cycle can take from 18 to 72 hours. Mitosis has subphases as well.
Interphase -growth phase. longest phase of the cell cycle (90%) it is where the cell grows,
replicates, its DNA, and prepares for cell division,
G1 (first gap) - Longest phase of interphase and cell cycle, as the cell focuses on growth by
increasing its size and producing new organelles and proteins, it carries out regular function like
metabolism and waste removal, and prepares for DNA replication by making necessary proteins
and enzymes.
So essentially the cell gets bigger and makes things it needs to copy itself.
S (synthesis) – Each chromosome in the nucleus is copied to create two identical sister
chromatids that are joined at the centromere. This would also ensure that each daughter cell
receives a complete set of genetic information after cell division
So essentially the cell copies of all of its DNA so that it has two sets.
G2 (second gap) - Following DNA replication, cell undergoes final growth spurt and prepares
for mitosis, during G2, cell checks for any errors in newly replicated DNA and ensures
everything is easy for cell division
So essential the cell makes sure that everything is copied correctly and ready to divide.

Mitosis (M phase) - the replicated chromosomes (DNA) finally condenses and becomes visible
(under a microscope). The nuclear envelope starts to break down, spindle fibers attach to
chromosomes, and then the chromosomes are pulled to opposite sides of the cell by the spindle
fibers.
So essential the cells splits into two new cell each with one set of chromosomes.
Cytokinesis – the cytoplasm divides into two
What does the Mitotic Spindle function to do, what are the components that help the
mitotic spindles function as they should? Review the experiment conducted regarding how
kinetochore microtubules shorten during anaphase.
Fibers made of microtubules and associated proteins, the function of the mitotic spindle is to
separate the sister chromatids during cell division.
1. First, is the microtubule assembly
1. During cell division, protein structures called centrosomes initiates the assembly
of the microtubules. These microtubules extend outward from the centrosomes in
all directions, that would eventually form the spindle fibers
2. The centrosomes start making lots of strings (microtubules) that can reach in all
directions
2. Chromosome attachment
1. Motor proteins within the spindle fibers capture the kinetochores, which are
protein complexes that are attached to centromeres of chromosomes.
2. Each sock (chromosome) has a tag (kinetochore) that the strings can grab onto.
3. Microtubule Tug of War
1. Spindle fibers excert pulling forces in opposite directions on the sister chromatids
through the kinetochore attachments
i. Some strings pull one sock (sister chromatid) towards one side of the cell,
,and the other strings pull the other sock (sister chromatid) towards the
opposite side. Motor proteins help with the pulling.
4. Anaphase
1. As mitosis progresses to anaphase, some microtubules disassemble and shorten,
while others lengthen, this coordinated pulling and pushing by the microtubules
help separate the sister chromatids towards opposite poles of the diving cell.
2. As things move along, some strings shorten while others grow longer. This helps
pull the socks (sister chromatids) all the way to opposite ends of the cell.
5. Completion of Mitosis
1. Once the sister chromatids reach opposite poles, mitosis is complete and the cell
can undergo cytokinesis, where the cytoplasm divides to form two daughter cells.
2. Once the socks (sister chromatids) are separated, the cell splits in two, creating
two new cells, each with a complete set of socks (chromosomes).
Components –
3. Kinetochores – protein complexes that are attached to centromeres of
chromosomes that serve as attachment points for spindle fibers
i. Think of kinetochores as tiny tags that sewn onto the socks
(chromosomes) The strings grab onto these tags.
4. Centrosomes – are microtubule organizing centers that are located near the
nucleus that initiate the assembly of spindle fibers
i. They are like knobs at the ends of a string, help the string grow in the right
direction
5. Microtubules are hollow cylindrical structures that made of proteins
i. These are like long strings of an machine. They are made of a protein
called tubulin and can grow and shrink
6. Motor proteins – proteins that move along microtubules and help pull
chromosomes towards opposite poles during anaphase.

i. Imagine these as little motors that walk along the string, pulling the socks
(chromosomes) in opposite direction.
Review the experiment conducted regarding how kinetochore microtubules shorten during
anaphase.
During anaphase, a chromosome is ‘walked’ along a microtubule as the actual microtubule
depolymerizes at its kinetochore end. This will cause a release of tubulin subunits.
The strings themselves aren't just pulling the socks, they're also shortening at the end to help
move the socks along.
Know the Stages of Mitosis, without the actual illustrations (descriptions of each phase as
they occur)
Prophase: Chromatin condenses into visible chromosomes. The nuclear envelope starts to break
down, and the nucleolus disappears. The centrosome replicates and begins moving to opposite
poles of the cell.
Prometaphase (optional stage): The nuclear envelope completely breaks down, chromosomes
become further condensed, and spindle fibers begin to attach to the centromeres of
chromosomes.
Metaphase: Chromosomes align at the center (equator) of the cell, attached to spindle fibers by
their kinetochores.
Anaphase: Sister chromatids separate and are pulled towards opposite poles of the cell by the
spindle fibers.
Telophase: Sister chromatids arrive at opposite poles and begin to decondense back into
chromatin. A new nuclear envelope forms around each set of chromosomes. The centrosomes
divide, and a cleavage furrow forms in the cell membrane.
What is Cytokinesis (how does it occur in Animal Cells, Plant Cells)?
Is the physical division of the cytoplasm after mitosis, resulting in two daughter cells.
- Animal Cells: A cleavage furrow forms at the equator of the cell, pinching inwards until
the cell is completely divided into two daughter cells. Microtubules and microfilaments
play a role in this process.
- Plant Cells: A cell plate forms along the midline of the dividing cell due to vesicles
accumulating from the Golgi apparatus. This cell plate eventually develops into the new
cell wall separating the two daughter plant cells.
What is Binary Fission?
Is type of asexual reproduction in which a single parent cell divides into two genetically identical
daughter cells. It's simpler than mitosis and occurs in prokaryotes (bacteria) and some archaea.
What are the Checkpoints of the Cell Cycle? G0, G1, S, G2, M. Where do they occur in
the Cell Cycle?
The cell cycle is a tightly regulated process with specific checkpoints to ensure proper DNA
replication and cell division.

- G1 checkpoint: Ensures the cell has grown enough and all external conditions are
favorable for DNA replication before entering the S phase.
- S phase checkpoint: Makes sure DNA replication is completed accurately before
entering mitosis.
- G2 checkpoint: Checks for DNA damage and ensures all chromosomes are properly
replicated before entering mitosis.
- M checkpoint: Ensures proper spindle fiber attachment to chromosomes before entering
anaphase.
What are Growth Factors, how are they released?
Signaling molecules released by certain cells that stimulate the growth and division of other
cells. They bind to specific receptors on the target cell's surface, triggering a signaling cascade
that leads to cell cycle progression.
What is Density-Dependent Inhibition, Anchorage Dependence?
Density-dependent Inhibition is a mechanism by which cells stop dividing when they reach a
high density in a confined space. Cell-to-cell contact or signaling molecules can inhibit further
growth and division.
Anchorage dependence is – some animal cells require a physical attachment to a substrate (e.g.,
extracellular matrix) to grow and divide. Detachment from the substrate can trigger cell cycle
arrest or apoptosis (programmed cell death).
Chapter 10
What is the difference between Asexual Reproduction vs. Sexual Reproduction?
Asexual Reproduction: Offspring are produced from a single parent. The offspring are
genetically identical to the parent (except for rare mutations). Examples include binary fission,
budding, and spore formation.
Sexual Reproduction: Offspring are produced from the fusion of gametes (sperm and egg) from
two parents. This results in genetic variation in the offspring due to the combination of parental
genes and the processes of meiosis and fertilization.
What are Genes, Gametes?
Genes: Genes are the basic units of heredity located on chromosomes. They contain the
instructions for building proteins and other molecules that determine an organism's traits.
Gametes: Gametes are specialized reproductive cells (sperm and egg) that contain half the
number of chromosomes (haploid) compared to the body cells (diploid) of the parent. This
allows for genetic variation during fertilization.
How many chromosomes do humans have, what makes us different species wise?
Humans have 23 pairs of chromosomes (46 total). Each pair contains homologous
chromosomes (one from each parent). The first 22 pairs are autosomes (non-sex chromosomes)
that determine various traits. The 23rd pair is the sex chromosomes (XX in females, XY in
males) that determine sex.
What is a Karyotype, how are they actually arranged?
A karyotype is a complete set of an organism's chromosomes arranged in a standardized
format (based on size, centromere position, and banding patterns). It provides information about
the number and structure of chromosomes, helping to identify chromosomal abnormalities.
What are Homologous Chromosomes, Sex Chromosomes, Autosomes?

Homologous Chromosomes: These are the paired chromosomes (one from each parent)
in a diploid organism that share similar genes but may have different alleles (versions) of those
genes.
Sex Chromosomes: These are the chromosomes (X and Y) that determine an organism's
sex. XX combination results in a female, and XY results in a male.
Autosomes: These are the non-sex chromosomes (22 pairs in humans) that carry genes
for various traits unrelated to sex.
What is a Diploid Cell, a Haploid Cell?
Diploid Cell: A cell with two complete sets of chromosomes (one from each parent).
Most body cells in animals, including humans, are diploid.
Haploid Cell: A cell with only one set of chromosomes. Gametes (sperm and egg) are
haploid cells.
How does the Human Life Cycle begin (animal), Plant, Fungi. Understand the variety of
the Sexual Life Cycles of each. What is an Alternation of Generations? Be familiar with
how they differ between the three.
• Animal Life Cycle:
o Begins with a fertilized egg (diploid) that undergoes development and cell
divisions (mitosis) to form a multicellular embryo.
o The embryo differentiates into various tissues and organs.
o Upon reaching maturity, the animal produces gametes (sperm and egg) through
meiosis, resulting in haploid cells.
o Fertilization of sperm and egg restores the diploid condition, restarting the cycle.
• Plant Life Cycle:
o Can be complex with alternation of generations (sporophyte and gametophyte).
o The sporophyte generation (diploid) produces spores through meiosis (haploid).
o Spores germinate into the gametophyte generation (haploid).
o The gametophyte produces gametes (sperm and egg) through mitosis.
o Fertilization of sperm and egg creates a zygote (diploid), which develops into a
new sporophyte, continuing the cycle.
• Fungi Life Cycle:
o Can also involve alternation of generations (haploid and diploid phases).
o The life cycle can vary depending on the fungal species.
Alternation of Generations:
This is a reproductive strategy in some plants and fungi where there's a switch between a haploid
(gametophyte) generation that produces gametes and a diploid (sporophyte) generation that
produces spores through meiosis.
Key Differences:
• Plants: The sporophyte generation is typically dominant and visible.
• Fungi: The dominance can vary between the haploid and diploid phases depending on the
species.

How does Meiosis reduce the number of chromosomes?
Meiosis: Reduces the chromosome number by half through two cell divisions, resulting in four
haploid daughter cells. This process is crucial for sexual reproduction to maintain the ploidy
level (number of chromosome sets) across generations.
Mitosis: Maintains the chromosome number by producing two genetically identical daughter
cells with the same ploidy level as the parent cell. This is essential for growth, repair, and
asexual reproduction.
What is Sister Chromatid Cohesion?
identical copies of a chromosome held together by proteins at the centromere until they separate
during anaphase of mitosis or meiosis II. This cohesion ensures the proper distribution of genetic
material to daughter cells.
What is Synapsis, where does it occur? What is Crossing Over?
- Synapsis occurs during prophase I of meiosis. It's the pairing of homologous
chromosomes along their entire length. Synapais allows for
o genetic exchange: During synapsis, a complex protein structure called the
synaptonemal complex forms between homologous chromosomes. This complex
facilitates the process of crossing over.
o Accurate chromosome segregation - Proper pairing ensures that homologous
chromosomes are correctly attached to spindle fibers during meiosis I, leading to
their separation into different daughter cells.
- Crossing over is a crucial event within meiosis that introduces genetic variation in
offspring. It occurs during synapsis when non-sister chromatids of homologous
chromosomes break at corresponding points and exchange genetic material.
o Breakage and Exchange: Non-sister chromatids break at homologous points
o Pairing and Rejoining: The broken ends of the non-sister chromatids from each
chromosome pair physically rejoin with each other, but in a "crossed-over"
fashion. This creates recombinant chromosomes with a mix of parental genes.
o Completion of Meiosis: After crossing over, homologous chromosomes separate
during anaphase I of meiosis, resulting in the formation of gametes with unique
genetic combinations.
o Genetic Variation: Crossing over creates new combinations of alleles on
chromosomes, leading to genetic diversity in offspring. This diversity is essential
for adaptation and evolution in populations.
o Increased Fitness: The new gene combinations generated by crossing over can
sometimes result in beneficial traits that enhance an organism's survival and
reproductive success.
o Crossing over can also lead to non-disjunction, a chromosomal abnormality where
homologous chromosomes fail to separate properly during meiosis.
Know the Stages of Meiosis, without the actual illustrations (descriptions of each phase as
they occur)
Meiosis I:

Prophase I: Chromosomes condense, homologous chromosomes pair up (synapsis) and
exchange genetic material (crossing over). The nuclear envelope breaks down.
Metaphase I: Homologous chromosome pairs align at the equator of the cell.
Anaphase I: Homologous chromosomes separate and move towards opposite poles of the
cell, resulting in the reduction of chromosome number by half.
Telophase I and Cytokinesis I: Two daughter cells form, each with a haploid number of
chromosomes (one from each homologous pair).
Meiosis II (similar to mitosis but with haploid cells):
Prophase II Chromosomes further condense and spindle fibers form.
Metaphase II: Chromosomes align at the equator of the cell.
Anaphase II: Sister chromatids separate and move towards opposite poles.
Telophase II and Cytokinesis II: Four daughter cells form, each with a haploid set of
chromosomes.
What is Independent Assortment of Chromosomes?
1. During Meiosis I, homologous chromosomes (except sex chromosomes) line up at the
equator of the cell (metaphase I).
2. Independent assortment refers to the random orientation of these homologous
chromosome pairs.
3. There's no specific pairing required at the equator.
4. Each homologous chromosome pair has a 50% chance of ending up on either side of the
cell during anaphase I, independent of the orientation of other chromosome pairs.
5. This random assortment process significantly increases the possible combinations of
chromosomes in the resulting gametes (sperm or egg).
What does Crossing Over achieve, what are Recombinant Chromosomes?
- Crossing over is the exchange of genetic material between non-sister chromatids of
homologous chromosomes during prophase I of meiosis.
- It physically breaks and rejoins the chromosomes, creating recombinant chromosomes
with a mix of parental genes.
- Crossing over is another mechanism that introduces genetic variation in offspring.
Recombinant Chromosomes –
These are chromosomes that have undergone crossing over.
They contain shuffled genetic material from both parental chromosomes. Recombinant
chromosomes contribute to the overall genetic diversity in offspring.
What is Random Fertilization?
- In sexual reproduction, fertilization involves the fusion of a sperm and an egg cell
- There's no predetermined sperm that fertilizes a particular egg.
- Millions of sperm compete, and the one that reaches the egg first fertilizes it, purely by
chance.
This randomness further shuffles the genetic makeup of the offspring.
Chapter 11

Who is Gregor Mendel? What did he achieve through his experiments?
Mendel is the founder of modern genetics
He discovered that parents pass on discrete heritable factors (genes) to their offspring.
That these factors do not blend even if they are present together in the offspring.
He discovered the basic principles of heredity
What is the ‘blending hypothesis’?
It is a hypothesis that genetic material from two parents blends together. (like yellow and blue to
make green), that parents pass on discrete heritable units (genes)
It it later rejected because it could not explain how traits disappear in one generation and
reappear in the next.
What are True Breeding plants? What is a hybridization?
True breeding - Plants that are when self-fertilized, such a plant produced offspring identical to
the parent.
(purple flower that when self-fertilzoied only produces purple flowers)
Hybridization - Breeding technique that involves crossing dissimilar individuals to bring together
the best traits of both organisms
Know P generation, F1 and F2 generations
P generation – parent plants are true breeding – Grandparents
F1- (1 st filial generation) – hybrid off spring – mom and dad
Hybrids – offspring that is produced by a cross from two different true breeding
F2 - (2 nd filial generation) – offspring prodyced when F1 plants fertilize each other (self-crossed
What is a Dominant trait, Recessive trait?
A dominant trait is a trait that masks over a recessive allele. (like a bossy sibling)
Recessive trait is a trait that is masked over a dominant. It needs a partner in crime, another
recessive allele to show.
Based on Mendel’s True Breeding Cross, what was the ratio in the F2 generation?
3 to one ratio.
What is a 3:1 Inheritance Pattern?
One PP, 2 Pp, and one pp.
P = purple flowers
P = white flowers.
What are Alleles? Where are they located on the Homologous Chromosomes?
Alleles are alternation versions of a gene. Each gene are located on a specific/same locus on a
specific chromosome.
What is the Law of Segregation?
Two alleles for a heritable character separate (segregate) during gamete formation and end up in
different gametes
So each organism inherits two copies of a gene, one from each parent
However, during gamete formation (sperm and egg cells), two alleles for a particular gene
segregate from each other
The segregation of alleles is random
So like imagine you have two different colored marbles (dominant and recessive alleles) in a
bag. When you pick a marble for a game (gamete formation), you only pick one at random, not
both.
What is the Law of Independent Assortment?
Alleles of different genes are inherited independently of one another. One gene segregates
(dominant or recessive allele ending up in a gamete) has no influence on how another gene
segregates

Like a pea with a plant with genes for seed color (yellow or green) and seed shape (round or
wrinkled)
The law of segregation explains how each gene separates its alleles when forming gametes
The law of independent assortment adds another layer. It says the separation of the seed color
allele (yellow or green) doesn’t affect the separation of seed shape allele (round or wrinkled).
They are sorted independently into gametes.
This allows for various combinations of traits in offspring, leading to a greater diversity of
phenotypes.
• Parent 1: Yellow, round seeds (YYRR)
• Parent 2: Green, wrinkled seeds (yyrr)
According to independent assortment, during gamete formation
• The yellow (Y) or green (y) allele for seed color can segregate independently from the
round (R) or wrinkled (r) allele for seed shape.
This results in four possible combinations of alleles in the gametes: YR, Yr, yR, and yr. When
these gametes combine during fertilization, the offspring can have various phenotypes like
yellow, round seeds (YRyr), green, round seeds (yRyr), and so on.
What is Phenotype, Genotype?
Phenotype is the physical makeup of an organism
Genotype is the genetic makeup of an organism
What is a Punnett Square, how is it used? What is a Testcross, how do you predict the
outcome based on known phenotypes?
Punnett square is a chart that is used to predict the likelihood of offspring genotypes and
phenotypes in a genetic cross between two parents. It can help visualize all possible
combinations of alleles (gene variations) that can be passed down.
A testcross is a breed experiment that helps discover the genotype of an organism with a
dominant phenotype. Since dominant traits can mask recessive alleles, a testcross helps reveal
the underlying genetic makeup.
How to understand the testcross works:
- Identify dominant phenotype: You want to know the genotype of an individual
dominant trait (e.g. tall plant).
- Choose a Recessive Parent: Breed the dominant indivudal with a parent know to the
homozygous recessive for the same gene
- Ratio of 1:1 (dominant:recessive) Indicates the dominant individual is heterozygous.
Predicting Outcome based on Phenotypes.
- By knowing phenotypes of the parents and assuming a specific inheritance pattern
(dominant-recessive) , you can use a punett square to predict them
Parents: Tall plant (dominant phenotype) x Short plant (recessive phenotype)
Punnett square: Shows a 1:1 ratio of tall and short offspring.
Explanation:
- Tall plant can be either homozygous dominant (TT) or heterozygous (Tt)
- Short plant is homozygous recessive (tt)
- Punnett square reveals only half of the offspring will inherit the dominant allele (Tt) from
the tall parent, resulting in tall phenotype.

- The other half will inherit two recessive alleles (tt) and have a short phenotype.
What is homozygous, heterozygous, genotype, phenotype?
Homozygous – two identical alleles of a gene
Heterozygous – two different alleles of a gene
Genotype – genetic makeup of an organism
Phenotype – physical makeup of an organism
What is a monohybrid, dihybrid, trihybrid? What does a monohybrid cross result in, a
dihybrid cross?
Monohybrid – breeding organisms that differ in one particular gene (e.g. crossing tall pea plants
with short pea plants, where heigh is controlled by a single gene.)
Dihybrid Cross – breeding organisms that differ in two particular gene. (e.g. crossing pea plants
with yellow, round seeds and green, wrinkled seeds, where seed color and seed shape are
controlled by two independent genes.
Trihybrid Cross – breeding organisms that differ in three particular genes. Trihybrid crosses
analysis is more complex.
A monohybrid cross can be analyzed in a Punnett square to predict the possible offspring
genotypes and phenotypes. In case of complete dominance, results will typically follow a 3:1
phenotypic ratio.
3: represents the offspring that will have the dominant phenotype
1: represents the offspring that will the recessive phenotype
TT, tt, Tt could be the results.
A dihybrid is more complex than a monohybrid. Will be a 4x4 typically in a 9:3:3:1 ratio.
• 9: Yellow, Round (YYRR, YYrr, YyRR, YyRr)
• 3: Yellow, Wrinkled (yyRR, yyRr)
• 3: Green, Round (yYrr, yYRr)
• 1: Green, Wrinkled (yyrr)
What does the 9:3:3:1 indicate? How does this differ from a 3:1 ratio?
9:3:3:1 – the phenotypic ratios of offsprings in a dihybrid cross (2 different genes)
3:1 phenotypic ratios of offsprings in monohybrid cross (1 gene)
What does the Multiplication Rule state?
Calculate the probability of independent events happening together. Indedependent events are
events that don’t affect each other’s likelihood of occurring
Like flipping a coin/roll a die, these are independent events because the outcome of the coin flip
doesn’t influence the outcome of the die roll.
P(A and B) = P(A) * P(B)
P(A and B) = probability of both event A and B happening
P(A)= probability of event A happening

P(B)= probability of event B happening
The multiplication rule to determine the probability of inheriting two specific dominant alleles
from parents.
What does the Addition Rule of Probability state?
Probability of at least one of two events happening, even if they are not mutually exclusive.
Mutually exclusive events are events that cannot happen at the same time.
P(A and B) = P(A) + P(B) – P(A and B)
P(A and B) = probability of both event A and B happening
P(A)= probability of event A happening
P(B)= probability of event B happening
P(A and B) is the probability of both event A and event B happening (subtracted to avoid
counting it twice).
The addition rule to determine the probability of having either a dominant or recessive phenotype
for a particular trait.
Be able to determine the Genetic Outcome based on data presented
What is Complete Dominance, Incomplete Dominance, and Codominance?
- Complete Dominance
o One allele (dominant allele) completely masks the expression of another allele
(recessive allele) for the same gene in an organism that has inherited both alleles.
The organism will only show the phenotype associated with the dominant allele.
- Incomplete Dominance
o Neither allele is completely dominant over the other. When an organism inherits
different alleles for a gene, resulting phenotype is a blend of phenotypes
associated with each individual allele.
§ E.g. red flower (dominant) x white flower (recessive) might result in pink
flowers (incomplete dominance)
- Codominance
o Both alleles are fully expressed in organisms phenotype. Results in mixed or
combined phenotype rather than singe dominant trait.
§ Like alleles for coat color in cattle can result in spotted coat pattern.
How does Multiple Alleles affect Blood Type? Be Prepared in determining a family
members potential allele.
- Three main blood alleles, A, B, O
- Individuals first inherit two alleles, one from each parent.
- A and B alleles are dominant over O. That would mean that a person with at least one A
or B allele will have a blood type A, B, or AB (codominance), while those with only O
alleles will have type O blood
- O is universal donor while AB is universal Acceptor
- To determine family member potential allele, you need Punnett squares and knowledge
of inheritance pattern (domainance/recessive or codominance).
- For example, if both parents have Type A blood, their children could have type A or O
blood, depending on the alleles they inherit from each parent. A Punnett square can be
used to calculate the probability of each offspring genotype and phenotype.
-

What is Pleiotropy?
- Single gene influencing multiple, unrelated phenotypic traits in an organism.
- Like a single gene wearing many hats!
What is Epistasis? How does this affect coat color in Labradors? Be prepared to
determine outcome based on data presented.
- Epistasis is when one gene (modifier gene) affects the expression of another gene.
Imagine a dimmer switch controlling the brightness of another lightbulb
- Coat Color in Labradors:
o Labrador Retriever Coat Color:
§ Labrador retrievers have three main coat colors: black, yellow and
chocolate. These colors are determined by a single gene with multiple
alleles.
§ The dominant allele (B) produces black fur, while a recessive allele (b)
determines yellow fur. A third allele (E) acts as a modifier gene.
o Epistasis Example:
§ Even though a dog might inherit two copies of the black allele (BB), if it
also inherits two recessive copies of the modifier gene (ee), its coat color
will be chocolate instead of black.
§ This shows how epistasis can alter the expected phenotypic outcome based
on the main gene.
What is Polygenetic Inheritance? What is usually expressed through this particular genetic
means?
Polygenetic Inheritance involves multiple genes, each contributes small effects, to
influence a single phenotypic trait. It’s like having an orchestra where many instruments
play together to create the final sound.
- Example
o Human Height: Many genes contribute to how tall a person becomes.
o Skin Color: Variation in several genes influence skin pigmentation
o Eye Color: Multiple genes determine eye color variations
Nature vs. Nurture, how does the environment effect of organism phenotypically? How
does this affect a particular plant?
- Nature: Refers to the genetic makeup of an organism, inherited form parents
- Nurture: Refers to environmental factors that can influence an organism’s phenotype
- Environmental Effects on Plants:
o The environment can significantly affect a plant’s phenotype through polygenic
inheritance.
o For example, a plant with genes for tall stature might not reach its fully height
potential if grown in poor soil conditions (nurture affecting nature)
What is a Pedigree Analysis? Determine the outcome of a Family Pedigree based on data
presented.
- Pedigree Analysis is a visual tool that helps trace the inheritance of a trait through
generations in a family.
- Squares and Circles represent males and females, respectively.
- Shaded symbols indicate the individuals with the trait being studied. (Affected)
- Lines connecting symbols shows parents and offspring.
- Offsprings are in birth order.
- Pedigree Analysis help predict the probability of inheriting a particular trait.
How do Recessive Disorders behave? How does the allele carry in a population?
- Disorders that are caused by inheriting two recessive alleles for a particular gene. If an
individual inherits one dominant and one recessive allele, they will typically be
unaffected (carrier) but can pass on the recessive allele to offspring.

- Carriers of recessive disorders often don’t show symptoms because they have at least one
dominant allele. However, they can still pass on the recessive allele to their children. The
frequency of carrier alleles in a population can influence the likelihood of a recessive
disorder appearing in offspring.
What causes Sickle Cell Disease, how does the presence of one allele affect the phenotype?
- Sickle Cell disease is a example of a recessive genetic disorder. It affects red blood cells
and causes various health problems
- Cause: In sickle cell disease, individuals inherit two recessive alleles (HbS) for the beta-
goblin gene, which is responsible for hemoglobin production in red blood cells.
- Effect of one allele: A single HbS allele (carrier) typically doesn’t cause symptoms.
What are Dominant Disorders? How are they caused?
- Dominant disorders require only one copy of a dominant allele to cause the condition.
Individuals with a dominant disorder will either inherit the dominant allele from one
parent or have a mutation in their own genes.
- Cause:
o Mutations:
§ Mutations in a gene can make it dominant, even if the original gene was
recessive.
o Gene Dosage:
§ Sometimes, having an extra copy of a gene (even if its normally recessive)
can cause a dominant disorder
What are Multifactorial Disorders, how are they caused?
- Multifactorial disorders are caused by a combination of genetic and environmental
factors. The specific genes involved and the environmental triggers can vary depending
on the disorder.
- Causes:
o Genetic Predisposition: Certain genes may increase an individual’s susceptibility
to a multifactorial disorder.
o Environmental Factors: Exposure to specific environmental factors (e.g. diet,
lifestyle) can interact with the genetic predisposition and trigger the disorder.
- Examples:
o Heart Disease: Genetic predisposition combined with diet, exercise, and lifestyle
factors.
o Cancer: Genetic mutations can be triggered by environmental factors like
radiation or chemicals
o Diabetes: Genetic predisposition can interact with factors like obesity and lack of
exercise.
Chapter 12
What is the Chromosome Theory of Inheritance?
- Proposed by Boueri and Sutton in the early 1900s, states that genes are found at specific
locations on chromosomes.
- Behavior of chromosomes during meiosis explains how traits are inherited according to
Mendelian genetics (dominant/recessive inheritance)/
- This theory provided a physical basis for the previously observed laws of inheritance.
What is the Law of Segregation (repeated from Ch 11)?
During gamete formation (meiosis), each gene gets separated form its pair, and only one
allele for each gene goes into each gamete (sperm or egg).
What is the Law of Independent Assortment (repeated from Ch 11)
During gamete formation, the inheritance of alleles for one gene does not influence the
inheritance of alleles for another independent gene.

These genes assort independently into gametes
How did Morgan’s Experiment in Fruit Fly’s determine certain traits expressed? What
was the common trait expressed, and what was is named?
- Morgan studied fruit flies (Drosophila) with eye color mutations
- He observed that the inheritance pattern of eye color did not follow the expected
mendelian pattern if the genes were on autosomes (non-sex chromosomes)
- Morgan’s experiments led to the discovery of sex-linked inheritance
Common trait:
Eye color was the common trait studied by Morgan.
He observed a white-eyed mutation that did not follow the expected inheritance pattern
for autosomal traits.
What are Sex-Linked Genes? What are X-Linked Genes?
- Sex-linked genes are located on the sex chromosomes (X and Y)
- X-linked genes refer specifically to genes located on the X chromosome.
- Males have only one X chromosome, so X-linked traits can be expressed differently in
male and females
What is X Inactivation? What is a Barr body?
- In female mammals, one of the X chromosomes in each cell is randomly inactivated
(turned off) to prevent females from having double the dosage of X-linked genes
compared to males.
- The inactive X chromosome condenses into a Barr body.
What are Linked Genes? How do they tend to be inherited together?
- Linked genes are genes located close together on the same chromosome.
- Because linked genes tend to stay together during inheritance (due to physical proximity
on the chromosome), they are often inherited together.
- However, genetic recombination can break the linkage.
What is Genetic Recombination, how was this discovered? Be prepared to determine
Frequency based on data provided.
- Genetic Recombination is the process by which linked genes can be separated and
shuffled during meiosis.
- This process creates genetic variation in off spring by generating new combinations of
alleles from parents.
- The discovery of genetic recombination helped explain why offspring sometimes inherit
traits that don’t follow the simple patterns of Mendelian inheritance.
How does crossing over contribute to recombination?
- Crossing over is a event during meiosis where homologous chromosomes exchange
genetic material
- The exchange contributes to genetic recombination by creating new combinations of
alleles on chromosomes.
What is a Genetic Map? How was it constructed? What is a Linkage Map? How was it
constructed?
- Genetic map is a visual representation of the relative positions of genes on a
chromosome.
- The distance between genes on a genetic map is measured in map units (m.u.).
- Linkage map is constructed by analyzing the frequency of recombination between linked
genes
- Higher the recombination frequency between two genes, the farther apart they are on the
chromosome (more map units)

What are Map Units?
- Unit of distance on a genetic map (m.u.)
- One map unit represents 1% chance of recombination between two linked genes during
meiosis.
How does Alterations of Chromosome Number cause genetic disorders?
- Alternations of chromosome numbers can cause genetic disorders. These alterations can
occur during meiosis.
What is Nondisjunction? Be prepared to determine where Nondisjunction occurs (Meiosis
I or Meiosis II).
- Nondisjunction is an error in meiosis where homologous chromosmes (or sister
chromatids) fail to separate properly.
- This can result in gametes with either an extra copy (trisomy) or a missing copy
(monosomy) of a chromosome.
- Nondisjunction can occur in either meiosis I or meiosis II, depending on the timing of
separation error.
What is Aneuploidy, Monosomic, Trisomy? What is an example of trisomy? What is
Trisomy 21?
- Aneuploidy is a condition where individual an abnormal number of chromosomes (other
than normal diploid number)
- Monosomy refers to having only copy of a chromosome instead of the usual two (missing
a chromosome)
- Trisomy refers to when having three copies of chromosome instead of the normal two
(extra chromosome)
- Example of Trisomy
o Down syndrome (Trisomy 21) is an common example of genetic disorder caused
by having extra copy of chromosome 21.
What are Alterations of Chromosome Structure? Know what happens in Deletion,
Duplication, Inversion, and Translocation.
- Alterations involve changes in the structure of individual chromosomes rather than total
number of chromosomes.
- Deletion: section of chromosome is missing. Can cause loss of genes and lead to various
problems depending on the deleted genes.
- Duplication: section of chromosome is present twice. Can cause disrupt gene balance
and cause abnormal development
- Inversion: segment of chromosome is flipped end-to-end. This may not always cause
problems, but it can affect gene expression or recombination.
- Translocation: segment of chromosome is translocated (moved) to a different
chromosome. This can disrupt the genes on both the original and recipient chromosomes.
What is Aneuploidy of Sex Chromosomes?
- Abnomal number of sex chromosomes (X and Y) in a individual
- Example
o Turner syndrome (X0): Females with only one X chromosome.
o Klinefelter syndrome (XXY): Males with an extra X chromosome
o Triple X syndrome (XXX): Females with three X chromosomes
o XYY syndrome: Males with an extra Y chromosome (mild phenotypic effects)
What Disorders are caused by Structurally Altered Chromosomes?
- Deletion: section of chromosome is missing. Can cause loss of genes and lead to various
problems depending on the deleted genes.
o Cri-du-chat syndrome (deletion on chromosome 5)
- Duplication: section of chromosome is present twice. Can cause disrupt gene balance
and cause abnormal development

o Charcot-Marie-Tooth-Disease (duplication of PMP22 gene on chromosome 17)
- Inversion: segment of chromosome is flipped end-to-end. This may not always cause
problems, but it can affect gene expression or recombination.
o Hemophilia A (inversion of X chromosome, disrupts a gene essential for blood
clotting factor VIII production)
- Translocation: segment of chromosome is translocated (moved) to a different
chromosome. This can disrupt the genes on both the original and recipient chromosomes.
o Chronic Mylogenous Leukemia (CML): translocation between chromosome 9 and
22. This would create a new fused gene that promotes uncontrolled growth of
white blood cells