Chapter 12: Genetics and Evolution

Question 1

Genes are organized into ____________. Each gene may have alternative forms called ________.

Answer 1

chromosomes; alleles

Question 2

Human beings typically possess two copies of each chromosome, called ____________.

Answer 2

homologues

Question 3

Each gene has a particular ____________, or location on a specific chromosome that is consistent across human beings - a gene can be described by its location.

Answer 3

locus

Question 4

Because each chromosome is part of a homologous pair, a person will inherit ____ alleles for all genes.

Answer 4

two

Question 5

If only one copy of an allele is needed to express a given phenotype, this allele is ____________.

Answer 5

dominant

Question 6

If 2 copies of a gene are needed, it is ____________.

Answer 6

recessive

Question 7

If both alleles are the same for a gene, the individual is said to have ________________ genotype.

Answer 7

homozygous

Question 8

If alleles are different, this is a ____________ genotype.

Answer 8

heterozygous

Question 9

If only one copy of an allele is needed to express a given phenotype, this allele is ____________.

Answer 9

dominant

Question 10

A ____________ genotypes describes a situation in which only one allele is present for a given gene, e.g. X chromosome in genotypical males.

Answer 10

hemizygous

Question 11

When only one dominant and one recessive allele exist for a given gene, there is said to be ____________ ____________.

Answer 11

complete dominance

Question 12

In complete dominance, the presence of one dominant allele will ________ the recessive allele, if present.

Answer 12

mask

Question 13

When more than one dominant allele

Answer 13

Codominance

Question 14

When more than one dominant allele exists for a given gene, there is ____________.

Answer 14

codominance

Question 15

In codominance, what can happen?

Answer 15

Can express both both simulatneously

Question 16

____________ dominance occurs when a heterozygote expresses a phenotype that is intermediate between the two homozygous genotypes.

Answer 16

incomplete

Question 17

____________ is a population measure defined as the proportion of individuals in the population carrying the allele who actually express the phenotype.

The probability that, given a particular genotype, a person will express the phenotype

Answer 17

Penetrance

Question 18

____ penetrance is when 100% of individuals with this allele express it.

Answer 18

full

Question 19

When most (but not all) of those with the allele express it, this is ________ penetrance.

Answer 19

high

Question 20

____________ is defined as varying phenotypes despite identical genotypes.

Answer 20

expressivity

Question 21

If expressivity is ________, the all individuals with a given genotype express the smae phenotype.

Answer 21

constant

Question 22

If expressivity is ________, then individuals with the same genotype may have different phenotypes.

Answer 22

constant

Question 23

What are the 4 basic tenets of Mendel’s first law of segregation?

Answer 23

1. Alleles exist
2. 2 alleles/gene, 1 from each parent
3. 2 alleles segregate during meiosis (gametes only have 1 allele for an inherited trait)
4. If 2 alleles are different, only 1 will be fully expressed, other 1 is silent.

exception to #4 is codominance and incomplete dominance

Question 24

What does Mendel’s second law of independent assortment state?

Answer 24

INheritance of one gene does not affect the inheritance of another gene

Question 25

The daughter strand is held to the parent strand at the ____________.

Answer 25

centromere

Question 26

Daughter + parent strands = ?

Answer 26

sister chromatids

Question 27

During prophase I of meiosis, homologous chromosomes pair up to form ____________.

Answer 27

tetrads

Question 28

What happens when tetrads come together? What is this called?

Answer 28

Small segments of genetic material are swapped between chromatids in homologous chromosomes, resulting in novel combinations of alleles that were not present in the original chromosomes. This is called recombination.

Question 29

Substances that cause mutations are called what?

Answer 29

Mutagens

Question 30

Elements known as ____________ can insert and remove themselves from the genome. What can this do to genes?

Answer 30

transposons; if it inserts itself in the middle of a coding sequence, the mutation can disrupt the gene

Question 31

________ mutations occur when one nucleotide is swapped for another. What are the 3 types?

Answer 31

point; 1. silent 2. missense 3. nonsense

Question 32

________ mutations occur when the change in nucleotide has no effect on the final synthesized protein.

Answer 32

silent

Question 33

Silent mutations most often occur when the changed nucleotide is transcribed to be the third nucleotide in a codon because there is ____________, or ________, in the genetic code.

Answer 33

degeneracy, wobble

Question 34

____________ mutations occur when the change in nucleotide results in subtituting one amino acid for another in the final protein.

Answer 34

missense

Question 35

____________ mutations occur when the change in nucleotide results in substituting a **stop** codon for an amino acid in the final protein.

Answer 35

nonsense

Question 36

____________ mutations occur when nucleotides are inserted into or deleted from the genome.

Answer 36

frameshift

Question 37

________ mutations occur when a large segment of DNA is lost from a chromosome

Answer 37

deletion

Question 38

Small deletion mutations are considered ________ mutations.

Answer 38

frameshift

Question 39

____________ mutations occur when a segment of DNA is copied multiple times in the genome

Answer 39

duplication

Question 40

____________ mutations occur when a segment of DNA is reversed within the chromosome.

Answer 40

inversion

Question 41

____________ mutations occur when a segment of DNA is moved from one chromosome to anotehr.

Answer 41

insertion

Question 42

____________ mutations occur when a segment of DNA from one chromosome is swapped with a segment of DNA from another.

Answer 42

translocation

Question 43

Genetic ________ is a flow of genes between species. Individuals from different but closely related species can mate to produce ____________ offpsirng.

Answer 43

leakage; hybrid

Question 44

Many hybrid offspring cannot do what? Why?

Answer 44

Cannot reproduce; often have odd numbers of chromosomes, which means homologous pairing cannot occur

Question 45

Genetic ________ refers to changes in the composition of the gene pool due to chance. It is more pronounced in what size populations?

Answer 45

drift; small

Question 46

The ____________ effect is an extreme case of genetic drift in which a small population of a species finds itself in reproductive isolation from other populations as a result of natural barriers, catastrophic events, or other ____________ that drastically and suddenly reduce the size of the population available for breeding.

Answer 46

founder; bottleneceks

Question 47

Inbreeding encourages ____________, which increases the prevalence of both homozygous dominant and recessive genotypes.

Answer 47

homozygosity

Question 48

The loss of genetic variation may caused reduce fitness of the population, a condition known as what?

Answer 48

inbreeding depression

Question 49

On the opposite end of the spectrum, ____________ is the introduction of unrelated individuals into a breeding group, which could theoretically result in increased variation within a gene pool and increased fitness of the population.

Answer 49

outbreeding

Question 50

What two genotypes are crossed in a test cross?

Answer 50

1. Unknown genotype 2. Homozygous recessive

Question 51

Tests crosses are sometimes called ________ crosses.

Answer 51

back

Question 52

Dihybrid cross of a two plants that are heterozygous for both traits will result in what ratio?

Answer 52

9:3:31

Question 53

____-________ traits are characteristics that are determined by genes located on the sex chromosomes

Answer 53

sex-linked (X-linked)

Question 54

Genotypical males have only one X chromosome and are ____________ for many genes carried on the X chromosome.

Answer 54

hemizygous

Question 55

An X chromosome carrying a defective allele is commonly given a ____________.

Answer 55

subscript

Question 56

The further apart two genes are, the more likely it is that there will be a point of crossing over, called a ________, between them.

Answer 56

chiasma

Question 57

The likelihood that two alleles are separated from each other during crossing over, called the ________________ ____________, is roughly proportional to the distance between the genes on the chromosome.

Answer 57

recominbation frequency

Question 58

Tightly linked genes have recombination frequences close to 0%; weakly linked genes have recominbation frequencies approaching ____%, as expected from independent assortment.

Answer 58

50

Question 59

A ____________ ________ representing the relative distance between genes on a chromosome can be constructed.

Answer 59

genetic map

Question 60

One ____ ________ or ____________ corresponds to a 1% chance of recombination occurring between two genes.

Answer 60

map unit; centimorgan

Question 61

How often an allele appears in a population is known as its ________ ____________.

Answer 61

allele frequency

Question 62

Evolution results from what?

Answer 62

Changes in gene frequencies in reproducing populations over time

Question 63

When gene frequencies of a population are not changing, the gene pool is stable and evolution is not occurring. What are the 5 criteria that are mandatory for this ?

Answer 63

1. Very large population (no genetic drift) 2. No mutations 3. Random mating (no sexual selection) 4. No migration in and out 5. All genes are equally successful at being reproduced

Question 64

If all 5 criteria are met to keep gene pool stable, a population is said to be in ________-____________ equilibrium, and equations can be used to predict the allelic and phenotypic frequencies.

Answer 64

Hardy-Weinberg

Question 65

What is the Hardy-Weinberg equation?

Answer 65

p^{2 + 2pq + q2 = 1 ## Footnote p2 = homozygous dominant frequency 2pq = heterzygous dominant frequency q2 = homozygous recessive frequency}

Question 66

The sum p^{2 + 2pq represents the frequency of what?}

Answer 66

dominant phenotype

Question 67

p + q =1 tells us what?

Answer 67

freqency of alleles

Question 68

p^{2 + 2pq + q2 = 1 tells us what?}

Answer 68

frequency of phenotypes

Question 69

# T = tall allele, t = short allele If T is p=0.80, what are the allele frequencies of the generation?

Answer 69

64% TT = 64% T and 0% t 32% Tt = 16% T and 16% t 4% tt = 0% T and 4% t Thus the allele frequencies are 80% T and 20% t

Question 70

Evolution is not equivalent to natural selection, what is their relationship?

Answer 70

Natural selection is a mechanism for evolution

Question 71

____________ ____________ is a process of favoring survival and reproduction of the fittest individuals in a population

Answer 71

differential reproduction

Question 72

____________ ____________ is a measure of an organism's success in the population, based on the number of offspring, success in supporting offspring, and the ability of offspring to then support otehers.

Answer 72

inclusive fitness

Question 73

____________ selection keeps phenotypes within a specific range by selecting against extremes.

Answer 73

stabilizing

Question 74

Adaptive pressure can lead to the emergence and dominance of an initially extreme phenotype through ____________ selection.

Answer 74

directional

Question 75

In ____________ selection, 2 extreme phenotypes are selected over the norm.

Answer 75

disruptive

Question 76

Disruprtive selection is facilitated by the existence of ____________ - naturally occurring differences inform between members of the same population.

Answer 76

polymorphisms

Question 77

____________ ____________ is a related concept that describes the rapid rise of a number of different species from a common ancestor.

Answer 77

adaptive radiation

Question 78

A ________ is defined as the largest group of organisms capable of breeding to form fertile offspring.

Answer 78

species

Question 79

# Reproductive isolation may occur in two different ways. ____________ mechanisms prevent formation of the zygote completely.

Answer 79

prezygotic

Question 80

# Reproductive isolation may occur in two different ways. ____________ mechanisms allow for gamete fusion but yield either nonviable or sterile offspring.

Answer 80

postzygotic

Question 81

What are examples of prezygotic mechanisms?

Answer 81

1. temporal isolation (breed at different times) 2. ecological isolation (different niches) 3. behavioral isolation (lack of attractino) 4. reproductive isolation (incompatibility of anatomy) 5. gametic isolation (fertilization can't occur despite intercourse)

Question 82

What are examples of postzygotic mechanisms?

Answer 82

1. hybrid inviability (formation of zygote that cannot developt to term) 2. hybrid sterility (forming hybrid offspring that can't reproduce) 3. hybrid breakdown (forming F1 hybrid offspring that are viable and fertile, but F2 are inviable/ infertile)

Question 83

____________ evolution refers to independent development of dissimilar characteristics in 2+ lineages sharing a common ancestor, e.g. seals and cats are both Carnivora but very different.

Answer 83

divergent

Question 84

________ evolution refers to the process whereby related species evolve in similar ways for a long period of time in resopnse to analogous environmental selection pressures

Answer 84

Parallel

Question 85

____________ evolution refers to the indpendent development of similar characteristics in 2+ lineages not sharing a recetn common ancestor, e.g. fish and dolphins both aquatic but different classes of vertebrates

Answer 85

convergent

Question 86

Molecular evolutions correlate the degree of genomic similarity with what?

Answer 86

amount of time since 2 species split off from same common ancestor

Question 87

The more similar the genomes of two species are, the more recently what? What is this called?

Answer 87

two species separated from each other; molecular clock model