Genetics and Evolution

Question 1

when does crossing over occur in meiosis?

Answer 1

during prophase I

Question 2

In meiosis I, prophase I, the nonhomolgous chromosomes (not the sister chromatids) align very precisely in synpasis. The paired chromosomes are called a ____ or _____

Answer 2

bivalent or tetrad

Question 3

distinguish between meiosis metaphase I and metaphase II

Answer 3

in metaphase I, the nonhomologus chromosomes are paired up at the metaphase plate, and it’s the nonhomolous pairs that are separated

in metaphase II, the sister chromatids (attached via a centromere) align at the metaphase plate and are separated from each other

Question 4

are the sister chromatids that separate during meiosis II identical?

Answer 4

No, not if the nonhomologous chromosomes underwent recombination during prophase I

Question 5

what is the synaptonemal complex (SC)?

Answer 5

this is a protein complex that attaches to the nonhomologous chromosomes in prophase I and align & attach them in a central region with another SC protein. This whole SC protein complex is required for crossing over

Question 6

movements in meiosis II are identical to those in mitosis, except that in meiosis II, the cells are ____, whereas the cells in mitosis are _____

Answer 6

haploid, diploid

*also note that the nonsister chromatids in metaphase II are nonidentical, whereas the sister chromatids in mitosis are identical

Question 7

when are the cells considered haploid in meiosis?

Answer 7

when the cells reach telophase I, they are considered haploid

Question 8

what is nondisjunction?

Answer 8

occurs when there is failure of chromosomes to separate during meiosis; gametes will either have 2 copies or no copies of a given chromosome. when they form a zygote, the zygote will therefore have either 3 copies (trisomy) or no copies (monosomy).

nondisjunction is not generally lethal, but typically results in sterility and organisms suffer intellectual disability

Question 9

distinguish between the law of segregation and law of independent assortment

Answer 9

law of segregation: refers to the 2 alleles of 1 gene (one allele on one chromosome and the other allele located on the other chromosome); each allele is separated and passed onto the next generation independently.

law of independent assortment: refers to 2 genes on different chromosomes, the alleles of one gene will separate independently from the alleles of the other genes

Question 10

What is the rule of multiplication in probability?

Answer 10

P(A & B) = P(A) x P(B)

this is the probability of both of 2 independent events happening concurrently, and can be found by multiplying the odds of either event alone

Question 11

what is the rule of addition in probability?

Answer 11

P(A or B) = P(A) + P(B) - (P(A) x P(B))

this calculates the chances of either of the 2 events happening: you add the chances of either event happening and subtract the probability of the 2 events occurring together

Question 12

Man genotype = bb & woman’s phenotype = Bb. What are the chances of an offspring being Bb genotype & be a boy?

Answer 12

P(Bb genotype) = 50%, or 1/2

P(boy) = 50%, or 1/2

Thus, P(A and B) = 1/2 x 1/2 = 1/4 = 25%

Question 13

distinguish between incomplete dominance and codominance

Answer 13

incomplete: a heterozygote is a blended mix of both alleles i.e. red and white alleles produces the color pink
codominance: 2 alleles are both expressed but are not blended i.e. blood types A and B

Question 14

explain the following terms:

1) pleiotropism
2) polygenism
3) penetrance
4) epistasis
5) recessive lethal alleles

Answer 14

1) pleiotropism: one gene effects many aspects of an organism’s phenotype that appear to be unrelated i.e. mutation in one gene may cause altered development of heart, bone, and inner ears
2) polygenism: one phenotypic trait is influenced by multiple genes i.e. height is influenced by growth factors, receptors, hormones, bone deposition, muscle development, and etc.
3) penetrance: describes the likelihood that a person w/ a given genotype will express the expected phenotype (a gene can have high, incomplete, or low penetrance) i.e. women who carry a breast CA gene will display variable rates of breast CA depending on their diet, and there also may genes at other loci that can affect the penetrance of the breast CA gene
4) epistasis: expression of alleles for one gene is dependent on a different gene i.e. curly hair gene cannot be expressed if a different gene causes baldness
5) recessive allele genes: mutant alleles can cause death of an organism when present in a homozygous manner. these genes typically code for essential gene products

Question 15

what is linkage?

Answer 15

refers to genes that are located on the same chromosome and therefore may not display independent assortment

Question 16

If alleles T & G and t & g are linked, and you cross TtGg and ttgg, what will be the phenotypic ratio of the offspring?

Answer 16

1:1 phenotypic and genotypic ratio in this scenario

Question 17

2 genes that express independent assortment & no linkage: what is the phenotypic ratio of crossing 2 heterozygous individuals TtGg x TtGg?

Answer 17

9:3:3:1

9 will be phenotypically dominant in both traits

3 will be phenotypically dominant in T, but phenotypically recessive in g

3 will be phenotypically recessive in t, but be phenotypically dominant in G

1 will be phenotypically recessive in both traits

Question 18

2 genes that express independent assortment and no linkage: crossing 1 heterozygote & 1 homozygote recessive individual will result in what phenotypic ratio?

Answer 18

1:1:1:1

phenotypically dominant in both

phenotypically dominant in gene 1, but recessive in gene 2

phenotypically recessive in gene 1, but dominant in gene 2

phenotypically recessive in both

Question 19

meiotic _____ provides the excpetion to gene linkage

Answer 19

recombination

Question 20

meiotic recombination produces new combinations of ____ not found in the parents and also allows genes located on the same ____ to assort independently

Answer 20

alleles, chromosome

Question 21

Equation for recombination frequency (RF)

Answer 21

RF = # of recombinants / total # offspring

Question 22

recombination frequency is proportional to the physical _____ between the genes and is used as a tool in gene _____

Answer 22

distance, mapping

Question 23

If the following individuals are crossed: BBGG, and bbgg, and there is linkage between the genes. If an offspring expresses a phenotypic recessive trait, did recombination occur?

Answer 23

No, a mutation must have occured. even if each parent recombined their nonhomologous chromosomes, they could still only produce BBGG and bbgg genes.

Question 24

autosomal dominant: skips or does skip generations? # affected males about the same or different than # affected females?

autosomal recessive: skips or doesn’t skip generations? # affected males about the same or different than # affected females?

Answer 24

autosomal dominant: does not skip generations, # affected males are about the same to # affected females

autosomal recessive: can skip generations (affected individuals can have unaffected parents), # affected males are usually = # affected females

Question 25

mitochondrial inheritance patterns:

1) all mitochondria are inherited from ____
2) how many/which children are affected?

Answer 25

1) female
2) all children will be affected if mother is affected. none of children will be affected if father is affected, but mother is not

Question 26

distinguish between Y-linked, X-linked recessive, and X-linked dominant

Answer 26

Y-linked: only affects males and affected father has all affected sons. unaffected father cannot have affected sons

X-linked recessive: can skip generations, tends to affect males more than females; unaffected females can have affected sons; affected female has all affected sons, but can have either affected or unaffected daughters (depending if the father is affected)

X-linked dominant: does not skip generations, usually affects males > females (an affected individual must have an affected parent); usually affects males >females; affected fathers have all infected daughters (but will have unaffected sons if mother is unaffected); affected mothers can have affected or unaffected sons/daughters

Question 27

what is a gene pool?

Answer 27

the sum total of all genetic information in a population

Question 28

equation for allele frequency

Answer 28

allele frequency = # of allele X in a population / total # of alleles in a population

Question 29

What is the Hardy-Weinberg law?

Answer 29

sts the frequencies of alleles in a gene pool of a population will not change over time, provided several assumptions: there is no mutations, migrations, or natural selection; and that there is random mating & the population is large enough to prevent random drift

Question 30

If 100 homozygous green plants & 100 yellow homozygous plants (recessive) are crossed, and 1,000 green pea plants are produced. What is the allele frequency of the yellow alleles?

Answer 30

50%

Note that the allele frequency of the parent generation and of the F1 generation will remain the same, even though phenotypic traits differ. This ratio will still remain 50% even 4 generations from the F1 generation

Question 31

Is independent assortment required for Hardy-Weinberg law?

Answer 31

No. even for linked genes, recombined or not, will not affect the allele frequency of a population.

Question 32

According to the Hardy-Weinberg law, what will happen to the frequency of yellow allele (recessive) if predation occurs on yellow plants, but yellow plants attracts bees more successfully?

Answer 32

Hardy-Weinberg says nothing about this situation. Once the assumptions no longer hold true, Hardy-Weinberg no longer applies.

Question 33

What are the 2 Hardy-Weinberg equations?

Answer 33

p² + 2pq + q² = 1

this represents the genotype proporions in a population. All must add up to 1 since it’s a proportion.

p + q = 1

this represents the allele frequency. all allele frequency must add up to 1 because only there are only 2 alleles make up a gene in a diploid.

Question 34

both allele frequency and ____ frequency will remain constant over time according to Hardy-Weinberg

Answer 34

genotype

Question 35

a population reaches Hardy-Weinberg equillibrium after __ generation(s)

Answer 35

one

P = GG x gg ⇒ F1

F1 & F2 will have the same genotypic ratio

Question 36

what does fitness of an organism refer to?

Answer 36

refers to how successful an organism is in passing on its alleles to future generations of the population

Question 37

If a polar bear develops CA after its reproductive years, will this influence it’s fitness?

Answer 37

no, because that organism’s genome is still passed on to offspring and the CA doesn’t occur until after it’s reproductive years

Question 38

can natural selection create new alleles?

Answer 38

no. only mutation can create new alleles. natural selection can only affectt already existing alleles

Question 39

polygenic traits often follow a bell shaped curve. explain how this bell shped curve is r/t dirrectional selection, divergent selection, and stabilizing selection

Answer 39

dirrectional selection: natural selection removes one one of the extreme, & the population over time will move in the other direction i.e. taller giraffes get taller and shorter giraffes die off because lack of food

divergent selection: natural selection removes the members near the average, leaving the 2 exremes, which over time may perhaps lead to a new species

stabilizing selection: both extremes are selected against, driving the population closer to the average

Question 40

explain artificial selection, sexual selection, and kin selection

Answer 40

artificial: humans intervene in animal/plant mating to achieve desired traits

sexual selection: animals don’t choose mates randomly, but have evolved rituals and physical traits that play in attracting a mate

kin selection: social animals may sacrifice themselves for the sake of the alleles they share with another individual (family) i.e. a female lion sacrifices herself to save her sister’s children

Question 41

2 individuals are not members of the same species if they cannot produce _____

Answer 41

fit offspring

Question 42

what is reproductive isolation

Answer 42

this keeps existing species separate via either prezygotic or postzygotic barries

Question 43

distinguish between prezygotic and postzygotic barriers

Answer 43

prezygotic prevent formation of a hybrid zygote via ecological, temporal, behavioral, mechanical/physical structure, or gametic structure prevent breeding

postzygotic: prevent the development, survival, or reproduction of hybrid individuals and, therefore, prevent gene flow if fertilization between 2 different species; there is hybrid invariability, hybrid sterility, and hybrid breakdown (hybrid offspring is biologically defective)

Question 44

what is speciation?

Answer 44

creation of a new species