Final Exam Bio Modules 1-3

Mitosis Arrangement

Physical Arrangement happens on the metaphase plate where chromosomes align themselves

Mitosis Chromosome Number

Number of chromosomes stays consistent throughout mitosis, so the number of chromosomes in daughter cells will be the same as original cell

(parent: 46 chrome. and 92 chroma. Daughter: 46 chrome and 46 chroma)

Mitosis: chromosome number sequence example

1. G1: 8 chromosomes and 8 chromatids

2. S Phase: 8 chromosomes and 16 chromatids

3. During Mitosis: 8 chromosomes and 16 chromatids

4. After Mitosis: 8 chromosomes and 8 chromatids

Meiosis Arrangement

1. Metaphase 1: chromosomes align on metaphase plate and go through independent assortment (leads to variations which is expressed by: 2^n)

2. Prophase 1: chromosomes from mom and dad swap segments of each other to each other via crossing over aka recombination

Variation Equation

2ⁿ: n represents haploid number. Example, humans have 2²³: 8 billion variations of independent assortment

Meiosis Chromosome Number

DNA duplicates in S-Phase of Interphase. The number of chromosomes stay the same as parent cell. But after cytokinesis and telophase 1, number of chromosomes in each daughter is reduced by half and this reduction number is maintained through telophase 2 and cytokinesis, producing haploid gametes.

Meiosis: chromosome number sequence example

1. G1: 4 chromosomes and 8 chromatids

2. S phase: 8 chromosomes and 16 chromatids

3. Meiosis 1: 4 chromosomes and 8 chromatids

4. Meiosis 2: 4 chromosomes and 4 chromatids

Independent Assortment

Randomly distribute homologous chromosome pairs into daughter cells creating unique combinations in gametes

Recombination

creates new combination of alleles on the same chromosomes by physically exchanging segments of themselves between homologous chromosomes

Asexual Reproduction

Daughter cells are reproduced to be identical to original cell. Parent organism passes all of its genes to its offspring creating identical copy of itself

Asexual Reproduction in Plants: Tubers

food storage for a plant but can serve as a way to reproduce identical plants seen in potatoes (“Eyes”)

Asexual Reproduction in Plants: Runners

Long stems that bears identical daughter plants that grow form these runners

Asexual Reproduction in Plants: Bulbs

Food storage which daughter cells can grow from seen in onions

Asexual Reproduction in Bacteria: Budding

a daughter cell plan buds from the original parent cell or plant and grows enough to pop off the parent plant or cell to become its own individual yet identical to original cell

Asexual and Artificial Reproduction: Cutting

pieces or segments that are cut from parent plant or cell that can grow and develop by itself without being attached

Asexual and Artificial Reproduction: Micropurgation

Plant tissue is placed in a pastry dish at a controlled environment to be allowed to grow into new plants using hormones and nutrients

Asexual Reproduction relies on

mitosis

Asexual Reproduction: Pros

Speedy process because only one organism is needed

Asexual Reproduction: Cons

Genetic uniformity might be preferred in horticulture, but makes crops susceptible to diseases (bananas, potato famine)

Sexual Reproduction

2 parents, each providing 1 gamete (sperm and egg), create a zygote through fertilization (sperm and cell fuse together) that develops into an organism

Sexual Reproduction in Animals

1. At fertilization, both sets of DNA (mom and dad) unite and fuse to create a new cell with combination of each parent called a zygote

2. A zygote will duplicate itself via mitosis to create identical daughter cells for growth and development

Sexual Reproduction in Plants

1. Male sperm is pollen and female egg are ovules. Both come together to form a zygote

2. A fertilized ovule creates a seed which then develops into a plant

3. Fungi, plants and animals undergo sexual reproduction

Haploids and Gametes

Gametes are considered Haploids (n) and when they fuse together to create a zygote via fertilization, they are then a diploid (2n)

Sexual Reproduction: cons

time consuming, need two gametes to fertilize and create organism

Sexual Reproduction: pros

different genes mean different expressed characteristics and increases fittest of environment chances which then increases their fitness

cells spend a longer time in the

interphase

Without taking crossing-over into account, how many different chromosomal configurations can be produced in gamete cells from a diploid cell with diploid number 2n = 4?

4

2n=4

n = 2 via division

2² = 4

Without taking crossing-over into account, how many different chromosomal configurations can be produced in gamete cells from a  diploid cell with diploid number 2n = 6? 

8

2n=6

n= 3 via division

2ⁿ = 2³= 8

List the two processes that create genetic variability during meiosis:

independent assortment and recombination (crossing over)

What is a third process in a sexual life cycle that creates genetic variability in the offspring?

Random Fertilization (a unique sperm out of 1 Million sperms fertilize a unique egg out of 1 Million eggs)

Mendel’s Principles of Inheritance

1st law of segregation and 2nd law of Independent Assortment

Mendel’s 1st Law of Segregation

Deals with a general feature with two specific forms that the feature can take. Example: seed color (character) can have 2 traits: green or yellow

Mendel’s 1st Law of Segregation: Gametes

when sex cells are made, the two copies of alleles for a gene separate (ex: blonde and brown hair alleles), so each gamete carries only one allele: Each gamete only gets one of the two alleles for that gene/trait

Mendel’s 1st Law of Segregation Main Idea

There is an equal chance for offspring to inherit either of the parent’s alleles

Mendel’s 1st Law of Segregation: How

Explains how traits are inherited and why a parent with two different alleles (heterozygote) has 50% chance of passing on each of those alleles to their offspring. Example, if we had 4 offspring, they will all inherit “A” allele from mom and they will all inherit “a’” allele from dad

Mendel’s 1st Law of Segregation: F2 generation

For the F2 generation, they will also have a 3:1 ratio, where 3 represents allele with the dominant allele: 1 dominant allele version (AA), 2 dominant heterozygote allele (Aa). The “:1” is the only recessive allele “aa”

Mendel’s 1st law location

Meiosis 1 in Anaphase 1

Mendel’s 2nd Law of Segregation

deals with 2 separate general features and each general feature is controlled by its own gene, which each gene has two alleles. Example: a seed has two general features, seed color and seed shape. Each general feature is called a gene which each one has two alleles (1 for yellow and 1 for green) (1 for round and 1 for wrinkle)

Mendel’s 2nd Law of Segregation: Gametes

when gametes are made, the alleles for one gene separate without affecting how the allele for another gene separates. Example: the seed color (Y y) will not influence the separation of shape (R r) so both alleles are separating independently

Mendel’s 2nd Law of Segregation Rules of independent assortment

1. applies to genes that aren’t close (linked genes) or far apart from each other

2. but when genes are located near each other on the same chromosome tend to be inherited together (Y and R are close to each other so they will be inherited together than Y r and y r)

3. Non-homologous chromosomes assort themselves independently during meiosis 1 in metaphase 1

P generation

2 true breeds (AA or aa)

F1 generation

hybrid; heterozygote generation (Aa)

F2 generation

cross between AA, Aa and aa. Ration is always 3:1

Homologous Chromosomes

same shape and length; same gene different allele

Non- Homologous Chromosomes

different length; different gene different allele

Mendel’s 2nd Law location

Meiosis 1 Metaphase 1

Generate the Punnett Square for a first generation: Aa x Aa

AA, Aa, Aa, aa

phenotype: 3:1

genotype: 1:2:1

Generate the Punnett Square for a first generation: AA x aa

Aa

phenotype: 4:0

genotype: 0:4:0

Generate the Punnett Square for a first generation: Aa x aa

Aa, aa

phenotype: 2:2 or 1:1

genotype: 0:2:2

Problem #1:

In pea plants, purple flowers (P) are dominant to white flowers (p). Two heterozygous plants (Pp) are crossed.

PP= 1

Genotype ratio: 1:2:1

Pp= 2   

Phenotype ratio: 3:1

pp= 1

Problem #2

In guinea pigs, short hair (S) is dominant over long hair (s). A short-haired guinea pig is crossed with a long-haired guinea pig.

Ss

Problem #3

In snapdragon flowers, petal color shows incomplete dominance.

• RR = red petals
  
  

• Rr = pink petals
  
  

• rr = white petals
  
  

A cross is made between a pink-flowered plant and a white-flowered plant. Explain why incomplete dominance produces more phenotypic variation than simple dominance.

Rr, rr

Incomplete dominance increases the observable vartion in phenotypes because each genotype results in a distinct phenotype. For example, in incomplete dominance the homozygous dominant, heterozygous, and homozygous recessive genotypes all appear different (e.g., red, pink, and white flowers). In contrast, with simple dominance the heterozygous and homozygous dominant genotypes share the same phenotype, reducing the number of visible variations.

Show how a Punnett square is related to meiosis and fertilization: Meiosis

During meiosis, gametes (sperm or egg cells) are produced. Each gamete receives one allele for each gene from the parent because homologous chromosomes separate during meiosis (law of segregation). The alleles listed along the top and side of a Punnett square represent these gametes.

how how a Punnett square is related to meiosis and fertilization: Fertilization

Fertilization is the process where two gametes combine to form a zygote. Each box in the Punnett square represents a possible combination of alleles from the egg and sperm — essentially modeling all possible outcomes of fertilization.

 Recognize that dominance does not equal prevalence.

Dominance is how alleles interact, not how frequent they are in the population

Molecular Basis: Dominant Traits

Dominant is an allele whose trait appears in a heterozygote (doesn’t mean stronger or more common), meaning they are produced enough to show an effect

Molecular Basis: Dominant Traits Mutation

Result from a gain-of-function mutation meaning mutated gene produces a protein that does something new, extra or abnormal. Example: Hungtinton’s Disease is a dominant mutation which creates a toxic protein which is rare but only needs one dominant copy to show

Molecular Basis: Recessive Traits

an allele whose trait is masked in a heterozygote and only appears if there are two copies of recessive allele present. It is a result from loss-of-function mutation where one working copy is enough to mask the effect

Molecular Basis: Recessive Traits Mutation

result from a loss-of-function mutation meaning the mutated gene produces less protein, nonfunctional protein or no protein at all. Example: CFTR protein is nonfunctional if both gene copies are mutated. Need two copies of mutated gene to show trait because one functional copy is enough to maintain normal function

Sex Linked

A trait or disorder caused by a gene located on a sex chromosome (X or Y)

X-linked recessive disorder

Are disorders located in the X chromosome and are more common in men than in women because since the gene is located on the X chromosome and males inherit 1 X from mom, the risk of gaining a disorder in the X is higher. Example: color blindness

Father (XY) with X-linked disorder

Father passes his X chromosome to all daughters and his Y to all sons. As a result, daughters inherit father’s X, so if his X carries the disorder, all daughters will at least be carriers if not affected. But, all sons will not be affected by father’s X-linked disorder

Mother (XX) with X-linked disorder

Mother passes one of her chromosomes to each child. Sons have 50% of inheriting an affected X so sons will express the disorder, but daughter’s, if not affected, will be carriers

Linked Genes

when some genes are located on the same chromosome. They tend to be inherited together if they are close to each other and Mendel’s 2nd law of independent assortment won’t hold true. Crossing over in Prophase 1 can break link so linked genes are no longer inherited together

Degrees of Dominance: Complete Dominance

dominant alleles completely masks the effect of recessive allele in heterozygote

Degrees of Dominance: Incomplete Dominance

heterozygote shows a phenotype that is intermediate between the two homozygotes. The dominant allele doesn’t completely mask. Example: Aa has a blend of traits rather than showing only dominant trait and each genotypes produces a distinct phenotype mirroring a 1:2:1 phenotype, so Rr shows a blended phenotype

Degrees of Dominance: Co-dominance

Both alleles in heterozygote are fully expressed so neither mask each other. Example: IA is an allele for A antigen and IB is an allele for B antigen. Genotype IAIB is an AB blood type where both A and B antigens are fully expressed on red blood cells and neither as masked. Shows both traits at the same time than blending

Multiple Alleles

More than 2 alleles exist for a single gene in a population, only thing is that each individual can only carry two of them. Each diploid individual still only carries at most two different alleles. Example: human blood; three alleles for the enzyme that attaches to red blood cells, genotype AB is an example of co-dominance and both affect phenotype in its own way

Gene disorder: Pleoitropy

Are responsible for multiple symptoms of certain hereditary diseases meaning one single gene influences multiple unrelated traits in an organism. Example: sickle cell disease is a result form sickle cell allele that causes substitution of single amino acid in hemoglobin proten in red blood cells that impair oxygen capacity, organ damage, strokes, etc.

Gene disorder: Epistasis

A gene affects phenotype expression of another gene due to interaction of gene products meaning expression of one gene masks or modifies the expression of another gene. Example: labrador retrievers have their hair color depend on two genes (one for hair color: black or brown. one for pigment: color or no color). Interaction between different genes and can alter expected mendelian ratios in offspring enough that some traits don’t follow mendelian ratios

Allele Frequency Equation

p+q = 1

Allele Frequency Equation: p

frequency of dominant allele, A

Allele Frequency Equation: q

frequency of recessive allele, a

Hardy-Weinberg equation

p²+2pq+q²

Hardy-Weinberg equation: p²

frequency of homozygous dominant, AA

Hardy-Weinberg equation: 2pq

frequency of heterozygote, Aa

Hardy-Weinberg equation: q²

frequency of homozygous recessive, aa

Question 1: 

In population of 1,000 flowers, 360 are dominant phenotype (AA or Aa) and 640 have recessive phenotype (aa). Predict how many individuals would have each genotype in the next generation if the population is in hardy weinberg equilibrium

• Dom: 360/1000= 0.36

• Rec: 640/1000= 0.64

• p^2= ?

• q^2= 0.64

• q^2= sqrt(q^2)= sqrt(0.64)= 0.8 

• 1-q= p -> 1 - 0.8= 0.2

• p= 0.2

• p^2 + 2pq + q^2

• p^2= (0.2)^2= 0.04

• q^2= (0.8)^2= 0.64

• 2pq= 2((0.2)(0.8))=0.32

1. p= 0.2 and q= 0.8

2. p^2= 0.04 , q^2= 0.64, and 2pq= 0.32

3. Prediction 

• Homo dom: 40

• Hetero: 320

• Homo rec: 640

Question 2: In a population of 500 rabbits, 49 show the recessive phenotype (white fur, aa) Calculate the allele frequencies p and q Determine the expected genotype frequencies (p^2, 2pq, q^2) Predict how many rabbits would have each genotype

• p^2  2pq + q^2

• p^2= (0.69)^2= 0.476 

• 2pq= 2((0.69)(0.31))= 0.428

• q^2= 0.098

• 0.47*500= 235

• 0.42*500= 214

• 0.098*500= 49

1. q= 0.69 and p= 0.31

2. p^2= 0.47 , 2pq= 0.42, q^2= 0.098

3. Prediction 

• Homo dom: 235

• Hetero: 214

• Homo rec: 49 

In absence of Hardy weinberg equilibrium, microevolution produces changes in allele frequencies across generation through 4 ways:

1. mutation

2. gene flow

3. genetic drift

4. natural selection

Hardy Weinberg equilibrium (no evolution)

1. no mutations

2. random mating

3. no natural selection

4. large population

5. no gene flow

Hardy Weinberg equilibrium: no mutation

no new alleles created in population gene pool and existing alleles do not change form one to another

Hardy Weinberg equilibrium: random mating

random mating means individuals in a population choose their mates by chance, with no preference for specific traits

Hardy Weinberg equilibrium: no natural selection

all genotypes within a population have an equal chance of survival and reproduction

Hardy Weinberg equilibrium: large population

it's big enough (essentially infinite) to prevent genetic drift, which are random, significant shifts in allele (gene variant) frequencies from one generation to the next, ensuring gene pools remain stable and predictable, a key condition for no evolution. Real populations aren't infinite, but very large ones minimize drift, acting like the theoretical ideal where allele frequencies stay constant. 

Hardy Weinberg equilibrium: no gene flow

there is no migration of individuals or alleles into or out of the population, which keeps the gene pool isolated. This prevents changes in allele frequencies caused by the introduction of new alleles from other populations or the removal of existing alleles from the population

evolution

change in genetic composition of a population generation to generation

microevolution

change in allele frequencies in a population over generations

Microevolution consists of 3 MAJOR PROCESS THAT ALTER ALLELE FREQUENCIES, ALSO KNOWN AS “MECHANISM OF EVOLUTION”:

1. GENE FLOW

2. GENETIC DRIFT

3. NATURAL SELECTION

Microevolution Major Process 1: Gene flow

• when individuals moves in and out of populations, carrying alleles with them which changes gene pool

• individuals or gametes that move to a new population carry their genes with them, introducing new genetic material into the recipient population’s gene pool (collection of total alleles)

What are some consequences of gene flow?

Tends to reduce variation between populations over time because it introduces genes from one population into another, mixing and equalizing allele frequencies, influencing homogenizing gene pools

However, it can increase genetic variation within a population by adding new alleles

Gene flow is NOT adaptive but it can alter fitness by

1. DECREASING FITNESS: natural selection tries to remove “bad” alleles that don’t fit the environment. but if individuals from another population keeps migrating in and bringing those alleles back, selection can’t get rid of them, making the population less adapted because the unwanted alleles keep coming back

2. INCREASING FITNESS: if one population evolves a beneficial allele (insecticide resistance) gene flow can spread the allele to other populations which increases fitness because it introduced helpful trait into new areas

Gene Flow and GMO (genetically modified organisms)

transgene escapes from GMOs when pollen from a genetically modified plant fertilizes a comparative wild relative, transferring transgenes via outcrossing (wind, animals) and can move through dispersal of seeds form GM crops to non GM crops. The escape of transgenes into the wild corners a fitness advantage, affects other farmer’s crops and leads to strategies to prevent and control spread of engineered plants

Microevolution Major Process 2: Genetic Drift

• changes in allele frequencies occur by chance where certain individuals reproduce, but not because they are inherently better. This is mainly after an unpredictable event occurs

What are some consequences of genetic drift?

it’s non directional process not driven by an alleles adaptive value meaning that beneficial alleles can be lost and harmful ones can become common out of luck. Smaller samples have a greater chance of random deviation from predicted results

Genetic Drift and Founder Effect

when a small number of individuals from a larger population break away to form a new isolated group. The gene pool will consist of only a subset of alleles present in original population leading to loss of genetic variation. Some alleles that were rare now can be common, leading to higher frequency of specific genetic disorders within a newly founded population

Genetic Drift and Bottleneck Effect

where a population’s size is drastically reduced leading to significant loss of genetic diversity. After a random event like a natural disaster, the original population represent a small random sample of the total gene pool. Loss of genetic material makes population vulnerable to disease and other changes. If population remains small, it may be further affected by genetic drift. Significant in small population, lead to loss of genetic variation within population but harmful alleles become “fixed”

What does it mean for alleles to be lost?

Means they can be lost forever if they is a complete wipe out of that allele and can only come back by two ways

1. mutation: very rare

2. gene flow: an individual with lost genes is reintroduced to population

best example of founder effect (small isolated population from a larger population)

Amish, an isolated group carried Ellis-Van Creveld Allele that causes dwarfism, palydactyly, and heart defects

best example of bottleneck effect (population size drastically changes due to a random event)

Loss of prairie chickens led to severe reduction in population of greater prairie chickens. Fewer than 50 survived with little genetic variation