BIOL 1030 Exam 3

LOOK AT THE CANVAS PAGE THAT SUMMARIZES THE STEPS OF CELL DIVISION. It lists the steps I want you to know for each of the three types of cell division: binary fission, mitosis, meiosis

know this!

What is the purpose of cell division in single-celled eukaryotes and prokaryotes? In contrast, what are the purposes {plural} in multicellular eukaryotes? {Hint: see the next question.}

cell division in single-celled organisms: is reproduction (binary fission)
cell division in multicellular organisms: include growth, development, and tissue repair.

Distinguish among the following terms: between parent cells and daughter cells, asexual reproduction vs growth, development (cell differentiation) and tissue repair (or regeneration). CONNECTION: What is the cellular result that NEEDS to happen in each of these situations?

Parent cells create daughter cells. Asexual reproduction requires only one parent and it creates identical daughter cells. CONNECTION: need to have identical cells to complete each of these****

Do prokaryote cells reproduce, sexually or asexually? What is the name of prokaryote cellular division?

Prokaryotic cells reproduce asexually and it is called binary fission

What are the three ways that Bacteria can exchange DNA with each other? How can the transferred DNA get integrated into the bacterial chromosome making a new recombinant chromosome (i.e., new combination of genes)?

1. transformation: new genes are incorporated into the cell by DNA taken from the surrounding environment
2. transduction: a transfer of genes from one bacteria cell to another by phage.
3. conjugation: a union of 2 bacterial cells or protists and a transfer of DNA between them

What are plasmids {HINT: module 10.23}? Is there only one type of plasmid?

Plasmids are small, extrachromosomal DNA molecules that are separated from the chromosomal DNA. Bacteria have genes on their plasmids.

What is the origin of replication?

refers to the specific sequence of DNA at which replication begins

What is the name of eukaryotic nuclear division versus cytoplasmic division? What is the main result of eukaryotic cell division in terms of # of cells, # and kinds of chromosomes, and nucleotide sequence?

Eukaryotic nuclear division is referred to as mitosis and cytoplasmic division is cytokinesis. Mitosis results in genetically identical daughter cells with the same number of chromosomes and same kind of chromosomes as parent cell.

Why is cell division so much more complicated for eukaryotes vs prokaryotes?

Cell division is much more complicated in eukaryotes because they have internal membranes and longer chromosomes than prokaryotes.

Demonstrate your understanding of the structure of a chromosome following terms by making labeled drawings: chromatin vs chromatid vs chromosome, histones vs euchromatin vs heterochromatin. Between unreplicated chromosome vs replicated chromosome, centromere, kinetochore, chromatid, and sister chromatids.

know this!

What is a karyotype? What is ploidy? How do you write ploidy down as a symbol (i.e., numbers and letters)? What is a haploid organism? What is a diploid organism? And what is an octoploid organism?

A karyotype: visual representation of the number and structures of the chromosomes in a cell
Ploidy: number of sets of chromosomes in a cell.
You write ploidy as 2n, or 4n, etc. A haploid organism (n) is an organism with 1 set of chromosomes. A diploid organism (2n) is an organism with 2 sets of chromosomes. An octoploid organism (8n) has 8 sets of chromosomes.

How many chromosomes (total number & number of pairs) do human somatic cells (non-gamete cells) have before and after mitosis? BIG PICTURE: So, in summary, what can you tell me about the ploidy of any kind of a human somatic cell before and after mitosis? Be prepared to compare this with meiosis.

Before mitosis, human somatic cells have 23 pairs of chromosomes, so 46 total chromosomes. After mitosis, human somatic cells have the same number of chromosomes and chromosome pairs because mitosis creates genetically identical daughter cells. This is diploid****

Give a definition for the cell cycle of eukaryotic cells. IOW, what does it describe? Distinguish between interphase, mitosis, and cytokinesis, and describe the sequence of events in the cell cycle (IOW, know the sequence of the cell cycle's events.). Describe what happens in G1, S, and G2 of interphase.

know this!

In what phase of the eukaryotic cell division is DNA replicated (as specific as you can)? In what phase does nuclear division occur? In what phase of the cell cycle does the replicated DNA get split between daughter cells?

DNA is replicated during the S phase of mitosis. Nuclear division begins during anaphase. During the mitotic phase (specifically anaphase) the replicated DNA gets split between the daughter cells.

Describe the mitotic spindle {spindle apparatus} that forms when a cell undergoes nuclear division in terms of its function and composition. Which animal cell structures are often associated with the spindle apparatus, and during what phase of mitosis are these structures replicated? Do plants have them?

The spindle apparatus is composed of microtubules. The spindle fibers attach to chromatids by protein complexes during pro-metaphase of mitosis.

Describe in detail the events that occur in prophase, prometaphase, metaphase, anaphase, and telophase of mitosis. Be sure you can identify these five phases of mitosis either from written descriptions of the events that occur in them or from diagrams. {look at the Canvas page called "Steps in Cell Division" to help you identify the relevant events.}

Prophase: the chromosomes condense and a spindle made of microtubles forms
Prometaphase: the nuclear membrane/envelope and nucleolus disappear; the chromsomes attach to the spindle fibers at their kinetochores
Metaphase: chromosomes line up at the center of the cell; meet in middle
Anaphase: centromere breaks and the sister chromatids move to opposite poles; apart
Telophase: the spindle disappears, chromosomes uncoil, nuclear membrane and nucleoulus reform on each side of cell
Cytokinesis: cleavage furrow occurs; splitting of the cytoplasm, 2 daughter cells

Describe in detail what happens when an animal versus a plant cell undergoes cytokinesis {they're different}. Make sure you include cleavage furrow and/or cell plate formation in your description and understand WHY they are different based on WHICH cellular structure one has that the other cell type does not.

Cytokinesis differs between animal and plant cells because plant cells have a cell wall, while animal cells do not. In animal cells, cytokinesis occurs through the formation of a cleavage furrow that splits the cytoplasm. In plant cells, because they have a cell wall, a cell plate forms in the middle to split the cytoplasm.

What two physical features control RATE of cell division in animal cells? IOW, what are the cells sensing in their surroundings? Why would a multicellular organism want to control the two physical features cells sense during growth in tissues? What happens if regulation of these two features goes wrong?

Anchorage and Cell Density. Anchorage refers to whether a cell is "anchored" or attached to something else to control cell division. Cell Density refers to the idea that if cells are touching or very dense in an area, then that would control cell division. If cell division is not controlled or regulated, then cells continue to divide, causing overgrowth, which is known as cancer.

What are the cell cycle checkpoints and what purpose do they serve? What does the cell "check" at each checkpoint, different for each checkpoint? {connect these ideas to your understanding of the cell cycle}

The checkpoints within the cell cycle are G1 , G2 , and M checkpoint. At the G1 checkpoint, the cell checks for growthfactors, cell size, and nutrient supply of the cell. At the G2 checkpoint, the cell checks whether the DNA was copied correctly and again checks the size of the cell. At the M checkpoint, the cell checks to make sure the chromosomes are connected to the spindle fibers.

Which of the stage or stages of interphase has a "switch" that controls whether a cell will divide or not? What are the three choices a cell can do at the end of G1 phase of interphase? If this control over cell division is lost, what disease condition usually results?

At the G1 phase, the cell decides whether to die, divide, or enter a resting state at G0 to become ready for replication. If control over cell division is lost, usually cancer results.

What is the function of growth factors and what type of molecules are they? How do they function in the flow of information within cells? Define signal transduction pathway.

They signal the cell cycle control system and are protein molecules that bind to receptor proteins, that then get passed through relay proteins to the cell control center.

What is apoptosis? Why is it good to control how a cell dies? IOW, what could harm the cell if it escaped?

Programmed cell death that occurs through a series of metabolic pathways so that it is controlled and keeps the contents of the dying cell controlled.

What is the difference between a benign tumor and a malignant tumor? What is metastasis? Why are malignant tumors almost always a more dangerous form of cancer?

A benign tumor does not invade the surrounding tissue, it remains at its origin. A malignant tumor can spread to various parts of the body and can rapidly grow. Malignant tumors are so dangerous because they can divide so rapidly and spread.

Distinguish between somatic cells and germ cells.

Somatic cells are body cells and germ cells are gametes (reproductive cells).

What are the names of the reproductive cells formed when animal cells undergo meiosis? {just the names}

Egg cells and sperm cells.

What is the overall objective of meiosis in terms of chromosomes?

Meiosis creates daughter cells with half as many chromosomes as the parent cells. Cuts ploidy in half*

Explain why a diploid cell has two chromosomes of each kind. IOW, where does each one come from (origin)?

In diploid cells, one set of chromosomes comes from each parent, so one from the mom and one from the dad.

Define homologous chromosomes. In this context, what is a gene locus? What is an allele?

Homolougous chromosomes are two identical chromosomes. A gene locus is the location of a gene pon a chromosome. An allele is a version of a gene at a locus.

Are the alleles at a gene locus located on homologous chromosomes always the same? What is the difference between a homozygous gene locus vs a heterozygous gene locus?

No, the alleles at a gene locus on homologous chromosomes do not always have to be the same. Gene loci are homozygous if the alleles at the locus are identical and they are heterozygous if the alleles are different.

How many homologous pairs of chromosomes do you have in your somatic cells, in your germ cells, in your gametes?

Somatic cells have 23 pairs of chromosomes and germ cells have 22 pairs of homologous chromosomes and 1 pair of sex chromosomes.

How many times does the nuclear material divide during meiosis?

Twice; produces 4 daughter cells.

How many daughter cells are produced from one diploid parent cell undergoing meiosis? Are these daughter cells diploid or haploid? And, are they genetically identical to each other? To the parent cell?

4 daughter cells are produced from one diploid parent through meiosis. These daughter cells are haploid. The are not genetically identical to the parent cells or to each other.

Describe in detail the events that occur in each phase of meiosis, giving each phase its proper name, and making sure you can identify each phase from drawings of a cell undergoing meiosis. Assume a diploid organism and use the following terms: homologous chromosomes, tetrad or bivalent, synapsis, crossing-over sister and non-sister chromatids, nuclear division, diploid, haploid.

Meiosis I - spliting of the homologous chromosomes
Prophase I: chromosomes condense, pairing of homolougous chromosomes into tetrads (synapsis)

Define gametogenesis, spermatogenesis, and oogenesis [two- to three-word answers]? What is the sequence of events in each? What are the products of each type of gametogenesis?

Gametogensis: cells undergo meiosis to form gametes.
Spermatogenesis: process that develops sperm.
Oogenesis: process that develops ovum.

What are the unusual events that occur during human oogenesis compared to spermatogenesis? Why do these events occur? At what stages of meiosis does oogenesis stop? What causes oofenesis to start again, different for each start point? When in a women's life cycle do oocytes stop during meiosis I? How about meiosis II? What is a polar body? What is disposed of in the first polar body? What is disposed of in the second polar body?

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Compare and contrast mitosis with meiosis by discussing: the number of daughter cells produced, the number of nuclear divisions, the chromosomes number at the end of the process, tetrad formation (pairing of homologous chromosomes) and crossing-over, types of cells that undergo each process, and the type of reproduction associated with each process (sexual vs asexual).

Mitosis is associated with asexual reproduction and it results in two genetically identical daughter cells, through one nuclear division. Each daughter cell will have the same number and same kind of chromosomes as the parent cell. Meiosis is associated with sexual reproduction and it results in four genetically unique daughter cells, through two nuclear divisions. Each daughter cell will have half the amount of chromosomes as the parent cell and it can vary because each daughter cell will have half of its chromosomes from each parent. In meiosis, tetrad formation occurs during prophase I and crossing over occurs here too.

What is the ultimate source of variation? (Looking Ahead: Remember this idea of ultimate to distinguish it from the primary sources of variation in sexually reproducing that occur during meiosis, next few slides.)

The ultimate source of variation is mutation of the DNA sequence

Explain how independent assortment of homologous chromosomes generates so much genetic variation.

it produces new combinations of alleles

Describe what happens during fertilization and the result -- include the names of the cells involved. Which cells are haploid and which are diploid?

two haploid gametes (egg and sperm) unite to form a diploid zygote

Explain how fertilization produces genetic variation.

Fertilization produces genetic variation because the zygote has a combination of chromosomes from both mom and dad. Additionally, sexual reproduction allows for the sorting of existing gene alleles which leads to more genetic variation.

After fertilization, what type of cell division does the zygote use to grow and develop into a multicellular adult?

After fertilization, the zygote divides through mitosis to grow and develop into a multicellular adult.

Can homologous chromosomes carry different versions of genes? IOW, carry different alleles?

Homologous chromosomes carry the same genes in the same locations, but they carry different versions of the same genes.

Which are genetically identical: sister chromatids or non-sister chromatids? Why?

Sister chromatids are genetically identical because they come from one original chromosome.

What is synapsis? In what phase of meiosis does crossing-over occur? What is the name of the chromatids of a tetrad (aka, bivalent) that are involved in crossing-over (sister or non-sister chromatids)? Do they come from the same parent of the individual? What are chiasmata? How does crossing-over produce new genetic variation?

Synapsis is the fusion of chromosome pairs at the beginning of meiosis. Crossing occurs during prophase I of meiosis and it occurs between two NON sister chromatids in a homologous pair. Crossing over occurs between a chromatid from each parent. Chiasmata are the points of contact between two non-sister chromatids during crossing over. Crossing over produces new genetic variation because the non-sister chromatids exchange genetic material at each chiasmata.

List the four sources of genetic variation in sexually reproducing organisms. Which one is the main source of genetic variation for haploid, asexually reproducing organisms? REVIEW: Which is the ultimate source of genetic variation for both types of organism? Which ones are the primary sources in sexually reproducing organisms? {look at the summary slide and take-home message slide}

Mutation ***** MAIN SOURCE OF GV IN ASEXUAL HAPLOID
Crossing over
Independent segregation
Fusion of gametes (fertilization)

What is nondisjunction? Describe what the results of meiosis are when nondisjunction occurs only in anaphase I compared to when nondisjunction only occurs in anaphase II. IOW, which of the two time points, where nondisjunction can occur, produces more abnormal gametes?

Nondisjunction refers to the failure of one or more homologous chromosomes OR sister chromatids to separate during nuclear division. Nondisjunction occurring in anaphase I produces more abnormal gametes than if it occurs in anaphase II.

What is a karyotype? How does a karyotype let us find alterations in chromosome numbers and structure? Distinguish between autosomes and sex chromosomes.

karyotype: a photo of all a person's chromosomes in a cell. It allows us to see abnormalities.
Autosomes: regular chromosomes that control the inheritance of NON sex-linked characteristics. Sex chromosomes determine the sex and sex-related characteristics.

Be able to describe and/or recognize a karyotype. Be able to explain how the sex of an individual human is determined {can be different in other organisms}. Which parent determines the sex of a human baby?

The sex of an individual is determined by the 23rd set of chromosomes. The father determines the sex of a human baby.

Explain sex-linked genes.

traits that are influenced by the sex of an individual.

Distinguish between individuals with a trisomy vs with a monosomy. IOW, how do these mutations relate to chromosomal numbers? Why is having too few or too many gene copies a problem?

Trisomy is three chromosomes in a set and monosomy is only one chromosome in a set. This creates a problem because cells will have trouble making the right amount of gene product. DOSAGE**

Understand how chromosomal number mutations lead to genetic disorders, such as Down Syndrome or Turner Syndrome.

Down syndrome: trisomy 21 which means it has an extra chromosome on the 21st set
Turner syndrome: monosomy as individuals with TS would only have one chromosome in the 23rd set (XO).

Name and describe the different types of structural mutations of chromosomes. {HINT: I mean changes to pieces of chromosomes, rather than whole chromosomes}. Contrast this type of mutation with point mutations {HINT: the size and number of nucleotides involved}. Can both types lead to frameshift mutations and, therefore, different polypeptide sequences?

Deletion: deletion of a piece of chromosome from the sequence ABC -> AC
Inversion: invert a piece of chromosomes (flip around) ABCDE -> ADCBE
Duplication: Duplication of a piece of chromosome ABCD -> ABBCD
Reciprocal Translocation: part of one chromosome attaches to another

How can polyploidy lead to new species of organisms? Which type of multicellular organisms have many polyploidy species {not frogs}? What capability makes it easier for these organisms to do this type of speciation {i.e., make them able to produce babies even with a duplication event}?

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List the types of mutations we discussed in this lecture. How do these mutations alter DNA sequence?

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Gene

basic unit of heredity

Gene Locus (Loci)

location of a gene on a chromosome

Allele

alternative forms of a gene

genotype

genetic makeup of an organism

Phenotype

physical makeup of an organism

Character and Trait. What two factors contributes the variation seen in any phenotypic character / trait (meaning what an organism looks like)?

character: a recognizable feature of an organism and a trait is a version of a character
Phenotype: influenced by genotype and the environment

Why is phenotype important?

because it refers to an organisms observable trait

What was Mendel's experimental organism? How many of its characters did he study? Name at least three of these characters. What are the two traits (character states) of each of the three characters you named?

Mendels experiment was based around the pea plant. He studied the height of the stem, the color and shape of the peas, the color and position of the flower, and the color and shape of the peapods. The height pof the stem was either tall or dwarf, the color of the peas was either yellow or green, the shape of the peas was either round of wrinkled, the peapods were wither inflated or constricted and the color of the pea pods was either green or yellow. Also, the flower color was either purple or white.

dominant allele

the gene/trait that has the ability to cover up or "mask" another

recessive allele

the gene that can be covered

Homozygous

BB or bb ; same

Heterozygous

Bb or Aa ; different

Homozygous dominant

AA or BB

Homozygous recessive

aa or bb

P generation

parent generation ; true breeding homozygous

F1 Generation

first offspring from P generation

F2 Generation

offspring of F1 monohybrid cross

What are Mendel's four hypotheses stated in modern terms {hint: Mendel did not know about DNA, we do. What terminology would we add?}?

1.alternative versions = alleles
2.inherit two alleles
3.domanince = phenotype
4.allele pairs separate during gametes production

True-breeding strain

P generation ; PP and pp

Hybrid Strain

F1 generation ; offspring of P generation/true breeding

Monohybrid Cross

F1 x F1

Define Mendel's law of segregation. Think about how alleles at gene loci segregate on chromosomes and end up in different gametes during meiosis. Then, think about how fertilization recombines those alleles.

Mendels law of segregation refers to the idea that a sperm or egg only carries one allele for each inherited character because allele pairs seperate during the production of gametes (anaphase 1 of meiosis**).

chromosome = molecule of DNA (IOW, one piece of DNA) + protein, gene = a small part of that molecule of DNA that codes for a functional molecule (RNA or polypeptide)

REMEMBER

What is probability, and why are large samples of offspring important when dealing with probability? Why is fertilization considered a "chance event"? Using an example problem, demonstrate how a Punnett square can be used to show all possible genotypes of the possible offspring of a genetic cross of parents with particular genotypes. Also, show how Punnett squares can be used to determine genotypic and phenotypic ratios of all the possible offspring (babies!) of a genetic cross. {How? Write out & work a problem.}

Probability: the likelihood of something to occur
Large samples of offspring are important because it allows us to get a better idea of the chances of offspring having certain traits.

What are the two rules of probability and how did I teach you to state the relationships of events to help you understand when to multiply and when to sum up the probabilities for each event {think 'AND' vs 'OR'}? Be sure to know how to set up genetics problems using these rules. {You will need this skill on the next exam for several problems.}

Two laws of probability: the multiplicative law and the additive law
multiplicative law: the probability of two independent events occurring together and it is done by multiplying their individual probabilities together (X AND Y)
additive law: the chance of an event that can occur in two or more independent ways is the sum of each events probability and it is done by adding the individual probabilities (X OR Y).

EXAMPLE PROBLEMS:

Work through Mendel's two successive monohybrid crosses (i.e., parental then F1 crosses) for flower color to show the genotypes and phenotypes in the F2 generation. Start with true-breeding plants having different flower colors (progeny = F1) and then with F1 hybrids (progeny = F2) by using your knowledge of meiosis, fertilization, genotypes, phenotypes, and by using letters to represent alleles and conventional symbols. Think and talk your way through the underlying biology.

On the problem set posted to CANVAS, be able to setup and work through genetic problems involving single loci {two and three trait crosses come next lecture} by using letters to represent alleles and by using conventional symbols. Depending on the question your solutions should include: the genotypes of the parents, possible gamete types, possible genotypes and phenotypes of the offspring, and the genotypic and phenotypic ratios of the offspring. Be able to calculate the probability of having particular traits from parents with specific genes. {Yes, Punnett squares work for this, but make sure you understand what it all means. If you practice setting up probability statements {Dr. E's "weird" long form}, you will gain a better understanding of the pieces need to solve the problems.

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As you work through and solve genetics problems, look for patterns. IOW, depending on what the question asks, how do you modify your approach to the solution? Types of questions: does the question ask for ALL possible genotypes, or ALL possible phenotypes, or only specific combinations of alleles for specific genotypes AND / OR specific phenotypes? IOW, the wording of the questions essential to understand how to set up the problem and solve it.}

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Define the following and write out an example of its/their genotype: F1 hybrid (mono- & di- & tri-), F1 dihybrid cross, F1 trihybrid cross.

F1 monohybrid cross: Aa x Aa
F1 dihybrid cross: AaBb
F1 trihybrid cross: AaBbCc

Describe the two trait crosses for seed color and seed texture (wrinkled or not) that Mendel performed between two true-breeding plants having different seed colors & seed textures (to get F1) and between two F1 dihybrids for seed color and seed texture (F2). What important law did Mendel formulate from his results of these dihybrid crosses?

Mendel performed an experiment on trait crosses for either green or yellow seed color and round or wrinkled seed texture. Mendel formulated the LAw of Inependent Assortment.

Define Mendel's law of independent assortment. Illustrate using letters for alleles & your knowledge of meiosis, chromosomes, and gene loci, how four different gametes are produced from a parent that is heterozygous for two traits that are on non-homologous chromosomes.

The law of Independent Assortment refers to the discovery that alleles of two or more genes get sorted independently of each other.

Be able to setup and work through genetic problems involving dihybrid & trihybrid crosses by using letters to represent alleles and by using conventional symbols. Your solutions should include: the genotypes of the parents, possible gamete types, possible genotypes and phenotypes of the offspring, and the genotypic and phenotypic ratios of the offspring. {You should work the problems using probability statements; a full Punnett squares too long and too prone to errors.} PRACTICE PROBLEMS AVAILABLE ON CANVAS {practice problem set 2}.

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Define testcross. Why would you want to perform a testcross?

A testcross is a test used to infer the genotype of an individual (BB or Bb) based on the offspring. You would want to perform a testcross if you need to know whether an individual is homozygous dominant for a trait or heterozygous. You need a dominant and a recessive genotype to determine whether the dominant individual is homozygous or heterozygous. If none of the offspring reveal the recessive trait, then the unknown genotype has to be homozygous dominant. If even one of the offspring shows the recessive trait, then the unknown genotype is heterozygous.

What are the genotypes of the individuals involved in a testcross and why do you need each one?

You need a dominant and a recessive genotype to determine whether the dominant individual is homozygous or heterozygous.

What are the possible results of a testcross? And, how are each these results interpreted in light of the REASON to perform a testcross?

If none of the offspring reveal the recessive trait, then the unknown genotype has to be homozygous dominant. If even one of the offspring shows the recessive trait, then the unknown genotype is heterozygous.

What is an autosomal chromosome vs a sex chromosome?

autosomal chromosome: non sex linked traits but a sex chromosome determines the sex of an organism and sex-linked traits.

Be able to explain how the sex of an individual human is determined, include the name of the system. Which parent determines the sex of the offspring? Explain sex-linked genes. Is this the only way that gender is determined in animals? Compare and contrast the other methods of gender determination in other organisms.

The sex of an individual human is determined by the X-Y system of sex determination. The dad determines the sex of the offspring. Sex-linked genes are located on the sex chromosomes. No, this is not the only way that gender is determined in animals. For some organisms, gender can be determined through environment, X-O, Z-W, and by chromosome number.

Be able to setup and work through sex-linkage genetic problems using letters to represent alleles and by using conventional symbols {do last questions the practice problem set 2}. The fruit fly eye color example is an excellent test of your knowledge.

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Why do human males express recessive sex-linked disorders more frequently than females? Why is the human Y chromosome useful in tracking human heritage?

Human males express recessive sex linked disorders more frequently that females because they only have one X chromosome. The human Y chromosome is useful in tracking human heritage because there is almost no opportunity for the Y chromosome to share its data with another chromosome, so all of the genetic information from a father is passed to his son.

Which genotypes would express a dominant autosomal disorder (i.e., dominant phenotype)? Which genotypes would express a recessive autosomal disorder (again, recessive phenotype)?

Dominant: AA and Aa
Recessive: aa

Be able to distinguish between an autosomal dominant and autosomal recessive disorder patterns in a pedigree (draw using symbols).

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What is a carrier? What is that carrier's genotype?

A carrier is someone who carries the gene for a certain disorder, but doesn't show it because it is masked by the dominant phenotype. A carrier's genotype is Aa heterozygous.

Explain how incomplete dominance works using petal color in snapdragons or hypercholesterolemia in humans. Why doesn't incomplete dominance support the blending hypothesis of inheritance {think F2 progeny}?

Regarding petal color in snapdragons, the colors red and white are incompletely dominant. The F1 offspring are pink because of the shared dosage. However, it is not considered a blend because the F2 offspring include a red and a white.

Define the term incomplete dominance in contrast to complete dominance.

Incomplete dominance: a mix of two dominant traits, not a blend but think DOSAGE**.

Define the terms multiple alleles and codominance. Explain how the ABO blood type system is an example of both multiple alleles and codominance. What are the three common alleles of the ABO blood system? What are the six possible genotypes and four possible phenotypes of the ABO blood system? Contrast codominance with incomplete dominance.

Multiple alleles: alternative forms of the same gene and they influence the same trait
Codominance: two versions (alleles) of the same gene expressed separately to yield different traits in an individual
In codominance, both alleles are visible separately but in incomplete dominance, you see more of a blend between the two dominant alleles because of dosage.

Contrast pleiotropy to polygenic inheritance.

Pleiotropy is different from polygenic inheritance because polygenic inheritance is when one gene is affected by many traits