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MCAT Biology > Chapter 12: Genetics and Evolution > Flashcards

Chapter 12: Genetics and Evolution Flashcards

1
Q

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

A

chromosomes; alleles

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2
Q

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

A

homologues

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3
Q

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.

A

locus

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4
Q

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

A

two

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5
Q

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

A

dominant

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6
Q

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

A

recessive

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7
Q

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

A

homozygous

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8
Q

If alleles are different, this is a ____________ genotype.

A

heterozygous

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9
Q

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

A

dominant

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10
Q

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

A

hemizygous

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11
Q

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

A

complete dominance

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12
Q

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

A

mask

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13
Q

When more than one dominant allele

A

Codominance

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14
Q

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

A

codominance

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15
Q

In codominance, what can happen?

A

Can express both both simulatneously

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16
Q

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

A

incomplete

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17
Q

____________ 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

A

Penetrance

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18
Q

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

A

full

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19
Q

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

A

high

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20
Q

____________ is defined as varying phenotypes despite identical genotypes.

A

expressivity

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21
Q

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

A

constant

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22
Q

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

A

constant

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23
Q

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

A
  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

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24
Q

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

A

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

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25
Q

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

A

centromere

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26
Q

Daughter + parent strands = ?

A

sister chromatids

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27
Q

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

A

tetrads

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28
Q

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

A

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.

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29
Q

Substances that cause mutations are called what?

A

Mutagens

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30
Q

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

A

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

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31
Q

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

A

point;
1. silent
2. missense
3. nonsense

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32
Q

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

A

silent

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33
Q

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.

A

degeneracy, wobble

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34
Q

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

A

missense

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35
Q

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

A

nonsense

36
Q

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

A

frameshift

37
Q

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

A

deletion

38
Q

Small deletion mutations are considered ________ mutations.

A

frameshift

39
Q

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

A

duplication

40
Q

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

A

inversion

41
Q

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

A

insertion

42
Q

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

A

translocation

43
Q

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

A

leakage; hybrid

44
Q

Many hybrid offspring cannot do what? Why?

A

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

45
Q

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

A

drift; small

46
Q

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.

A

founder; bottleneceks

47
Q

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

A

homozygosity

48
Q

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

A

inbreeding depression

49
Q

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.

A

outbreeding

50
Q

What two genotypes are crossed in a test cross?

A
  1. Unknown genotype
  2. Homozygous recessive
51
Q

Tests crosses are sometimes called ________ crosses.

A

back

52
Q

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

A

9:3:31

53
Q

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

A

sex-linked (X-linked)

54
Q

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

A

hemizygous

55
Q

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

A

subscript

56
Q

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

A

chiasma

57
Q

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.

A

recominbation frequency

58
Q

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

A

50

59
Q

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

A

genetic map

60
Q

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

A

map unit; centimorgan

61
Q

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

A

allele frequency

62
Q

Evolution results from what?

A

Changes in gene frequencies in reproducing populations over time

63
Q

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 ?

A
  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
64
Q

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.

A

Hardy-Weinberg

65
Q

What is the Hardy-Weinberg equation?

A

p2 + 2pq + q2 = 1

p2 = homozygous dominant frequency
2pq = heterzygous dominant frequency
q2 = homozygous recessive frequency

66
Q

The sum p2 + 2pq represents the frequency of what?

A

dominant phenotype

67
Q

p + q =1 tells us what?

A

freqency of alleles

68
Q

p2 + 2pq + q2 = 1 tells us what?

A

frequency of phenotypes

69
Q

T = tall allele, t = short allele

If T is p=0.80, what are the allele frequencies of the generation?

A

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

70
Q

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

A

Natural selection is a mechanism for evolution

71
Q

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

A

differential reproduction

72
Q

____________ ____________ 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.

A

inclusive fitness

73
Q

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

A

stabilizing

74
Q

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

A

directional

75
Q

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

A

disruptive

76
Q

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

A

polymorphisms

77
Q

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

A

adaptive radiation

78
Q

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

A

species

79
Q

Reproductive isolation may occur in two different ways.

____________ mechanisms prevent formation of the zygote completely.

A

prezygotic

80
Q

Reproductive isolation may occur in two different ways.

____________ mechanisms allow for gamete fusion but yield either nonviable or sterile offspring.

A

postzygotic

81
Q

What are examples of prezygotic mechanisms?

A
  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)
82
Q

What are examples of postzygotic mechanisms?

A
  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)
83
Q

____________ 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.

A

divergent

84
Q

________ 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

A

Parallel

85
Q

____________ 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

A

convergent

86
Q

Molecular evolutions correlate the degree of genomic similarity with what?

A

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

87
Q

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

A

two species separated from each other; molecular clock model

MCAT Biology (12 decks)

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