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MCAT: Biology > Chapter 12: Genetics and Evolution > Flashcards

Chapter 12: Genetics and Evolution Flashcards

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1
Q

What are chromosomes?

A

Genes in a linear sequence

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2
Q

What are alleles? Differentiate dominant and recessive alleles.

A
  • Alternative forms of a gene
  • Dominant: requires only one copy to be expressed
  • Recessive: requires two copies to be expressed
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3
Q

What is a genotype?

A

The combination of alleles one has at a given genetic locus

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4
Q

Differentiate homozygous, heterozygous, and hemizygous.

A
  • Homozygous: having two of the same allele
  • Heterozygous: having two different alleles
  • Hemizygous: having only one allele (ex: male sex chromosome)
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5
Q

What is complete dominance?

A

Has one dominant allele and one recessive allele

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6
Q

What is codominance?

A

Has more than one dominant allele

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7
Q

What is incomplete dominance?

A
  • Has no dominant alleles

- Heterozygotes have intermediate phenotypes (red + white = pink)

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8
Q

What is penetrance?

A

The proportion of a population with a given genotype who express the phenotype

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9
Q

What is expressivity?

A

Refers to the varying phenotypic manifestations of a given genotype across the population

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10
Q

What happens if expressivity is constant? What about variable?

A
  • Constant: individuals with the same genotype express the same phenotype
  • Variable: individuals with the same genotype may have different phenotypes
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11
Q

What is Mendel’s first law (of segregation)?

A

An organism has two alleles for each gene that segregate during meiosis, resulting in gametes that carry only one allele for any inherited trait

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12
Q

What is Mendel’s second law (of independent assortment)?

A

The inheritance of one allele does not influence the probability of inheriting a given allele for a different trait

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13
Q

What did the Griffith experiment demonstrate?

A

The transforming principle, converting non-virulent bacteria into virulent bacteria by exposure to heat-killed virulent bacteria

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14
Q

What did the Avery-MacLeod-McCarty experiment demonstrate?

A

That DNA is the genetic material because degradation of DNA led to a cessation of bacterial transformation

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15
Q

What did the Hershey-Chase experiment confirm?

A

That DNA is the genetic material because only radiolabeled DNA could be found in bacteriophage-infected bacteria

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16
Q

Which phase of meiosis does Mendel’s first law (of segregation) align with?

A

Anaphase I of meiosis

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17
Q

What phase of meiosis does Mendel’s second law (of independent assortment) most align with?

A

Prophase I of meiosis

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18
Q

Differentiate point mutations and frameshift mutations.

A
  • Point mutation: substitution of one nucleotide for another

- Frameshift mutation: moving the three-letter transcriptional reading frame

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19
Q

Elements known as _________ can insert and remove themselves from the genome

A

transposons

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20
Q

What are silent mutations? When do they most commonly occur?

A
  • Has no effect on the final protein synthesized
  • Commonly occurs when the changed nucleotide is transcribed to be the third nucleotide in a codon because there is degeneracy (wobble in the genetic code
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21
Q

When do missense mutations occur?

A

When the change in nucleotide results in substituting one amino acid for another in the final protein

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22
Q

When do nonsense mutations occur?

A

When the change in nucleotide results in substituting a stop codon for an amino acid in the final mutation

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23
Q

What do insertions and deletions result in? What does that lead to?

A

Results in a shift in the reading frame, leading to changes for all downstream amino acids

24
Q

When do deletion mutations occur?

A

When a large segment of DNA is lost from a chromosome

25
Q

When do duplication mutations occur?

A

When a segment of DNA is copied multiple times in the genome

26
Q

When do inversion mutations occur?

A

When a segment of DNA is reversed within the chromosome

27
Q

When do insertion mutations occur?

A

When a segment of DNA is moved from one chromosome to another

28
Q

When do translocation mutations occur?

A

When a segment of DNA from one chromosome is swapped with a segment of DNA from another chromosome

29
Q

What is genetic leakage?

A

A flow of genes between species through hybrid offspring

30
Q

What is genetic drift?

A

Occurs when the composition of the gene pool changes as a result of chance

31
Q

When does the founder effect arise? What does it lead to?

A
  • Results from bottlenecks that suddenly isolate a small population
  • Leads to inbreeding and increased prevalence of certain homozygous genotypes
32
Q

Differentiate a monohybrid cross and a dihybrid cross.

A
  • Monohybrid: accounts for one gene

- Dihybrid: accounts for two genes

33
Q

Crossing two heterozygotes for a trait with complete dominance results in what ratio for genotypes and phenotypes?

A
  • Genotypes: 1:2:1

- Phenotypes: 3:1

34
Q

What is a test cross?

A
  • Used to determine an unknown genotype

- The organism with an unknown genotype is crossed with an organism known to be homozygous recessive

35
Q

Crossing two heterozygotes in a dihybrid cross results in what ratio for phenotypes?

A

9:3:3:1

36
Q

Why are sex-linked traits more common in males?

A
  • Having only one recessive allele is sufficient for expression of the recessive phenotype
  • Sex-linked is X-linked
37
Q

What is the recombination frequency?

A

The likelihood of two alleles being separated during crossing over in meiosis

38
Q

How do tightly linked genes and weakly linked genes differ in terms of their recombination frequencies?

A
  • Tightly linked genes: 0%

- Weakly linked genes: 50%

39
Q

What are genetic maps? What is the scale? What is the unit of the scale?

A
  • Represent the relative distance between genes on a chromosome
  • Recombination frequency as the scale, in centimorgans
40
Q

What is allele frequency?

A

How often an allele appears in a population

41
Q

What are the five factors used to determine whether a population is not changing over time?

A

1) Large population (no genetic drift)
2) No mutations that affect the gene pool
3) Mating between individuals in the population is random (no sexual selection)
4) No migration of individuals into or out of the population
5) Genes in the population are all equally successful at reproducing

42
Q

What does the Hardy-Weinberg principle state?

A

That if a population meets certain criteria (aimed at a lack of evolution), then the allele frequencies will remain constant (Hardy-Weinberg equilibrium)

43
Q

How can we solve a Hardy-Weinberg equation?

A
  • Find the value of p (or p^2) or q (or q^2)
  • p + q = 1 (frequency of alleles in the population)
  • p^2 + 2pq + q^2 = 1 (frequency of genotypes and phenotypes in the population)
44
Q

What does natural selection state?

A

That chance variations exist between individuals and that advantageous variations, those that increase an individual’s fitness for the environment, afford the most opportunity for reproductive success

45
Q

What does the modern synthesis model (neo-Darwinism) account for? What does it consider to be the mechanism of reproductive success?

A
  • Accounts for mutation and recombination as mechanisms of variation
  • Considers differential reproduction to be the mechanism of reproductive success
46
Q

What is inclusive fitness?

A
  • A measure of an organism’s success in the population
  • Based on the number of offspring, success in supporting offspring, and the ability of the offspring to then support others
47
Q

What is punctuated equilibrium?

A

Considers evolution to be a very slow process with intermittent rapid bursts of evolutionary activity, rather than evenly over time

48
Q

What is stabilizing selection?

A

Keeps phenotypes in a narrow range, excluding extremes

49
Q

What is directional selection?

A

Moves the average phenotype toward one extreme

50
Q

What is disruptive selection?

A

Moves toward two different phenotypes at the extremes and can lead to speciation

51
Q

What is adaptive radiation?

A

The rapid emergence of multiple species from a common ancestor, each of which occupies its own ecological niche, decreasing competition for limited resources

52
Q

What is a species?

A

The largest group of organisms capable of breeding to form fertile offspring

53
Q

Species are reproductively isolated, in which progeny of the populations can no longer interbreed, through what mechanisms?

A
  • Prezygotic mechanisms: prevent formation of the zygote completely
  • Postzygotic mechanisms: allow for gamete fusion but yield either nonviable or sterile offspring
54
Q

What is divergent evolution?

A

Occurs when two species sharing a common ancestor become more different

55
Q

What is parallel evolution?

A

Occurs when two species sharing a common ancestor evolve in similar ways due to analogous selection pressures

56
Q

What is convergent evolution?

A

Occurs when two species not sharing a recent ancestor evolve to become more similar due to analogous selection pressures

57
Q

What does the molecular clock model state?

A

The degree of difference in the genome between two species is related to the amount of time since the two species broke off from a common ancestor

MCAT: Biology (12 decks)

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