Kaplan Biology: Chapter 12 - Genetics and Evolution

Bb × Bb phenotypic ratio

3:1

Aa × aa phenotypic ratio

1:1

DdEe × ddEE phenotypic ratio

1:1:1:1

XqX × XY phenotypic ratio

1:1 (carrier female × normal male)

XrX × XrY phenotypic ratio

1:1 (carrier female × affected male)

What is the recombination frequency (θ) roughly proportional to?

The distance between two genes on a chromosome

True or False: Sex-linked traits are more common in genotypical males.

True

A male has only one X chromosome. This makes him for X-linked traits.

Hemizygous

Which allele combination must a female have to express an X-linked recessive trait?

Two copies of the defective allele (homozygous recessive)

Equation for allele frequency in a population with two alleles (p + q

?)

Frequency of TT genotype in a population

p²

Frequency of Tt genotype in a population

2pq

Frequency of tt genotype in a population

q²

If p

0.8, q

True or False: Hardy–Weinberg equilibrium assumes evolution is occurring.

False

List one criterion necessary for Hardy–Weinberg equilibrium

No mutations

List another criterion necessary for Hardy–Weinberg equilibrium

Infinitely large population

List another criterion necessary for Hardy–Weinberg equilibrium

Random mating

List another criterion necessary for Hardy–Weinberg equilibrium

No migration

List another criterion necessary for Hardy–Weinberg equilibrium

Equal reproductive success

Define fitness in the context of natural selection

An organism’s relative genetic contribution to the next generation

Inclusive fitness measures

Offspring produced, success in supporting offspring, and the success of relatives

Which type of selection keeps phenotypes in a narrow range by selecting against extremes?

Stabilizing selection

Directional selection favors

One extreme phenotype

Disruptive selection favors

Two extreme phenotypes

Adaptive radiation

Rapid emergence of multiple species from a common ancestor occupying different ecological niches

Define species (biological definition)

Largest group of organisms capable of breeding to form fertile offspring

Prezygotic isolation

Prevents formation of a zygote

Postzygotic isolation

Allows gamete fusion but offspring are nonviable or sterile

Divergent evolution

Two species sharing a common ancestor become more different

Parallel evolution

Two species sharing a common ancestor evolve similarly due to analogous pressures

Convergent evolution

Two species not sharing a recent ancestor evolve similar traits due to analogous pressures

Molecular clock model

Degree of genomic difference correlates with time since divergence from common ancestor

A point mutation that changes a codon to a stop codon is called

Nonsense mutation

A nucleotide insertion or deletion that shifts the reading frame

Frameshift mutation

A large DNA segment reversed in orientation

Inversion mutation

A DNA segment copied multiple times

Duplication mutation

A mutation that swaps segments between two chromosomes

Translocation mutation

Genetic drift

Changes in allele frequencies due to chance

Founder effect

Bottleneck isolating a small population leading to inbreeding

Complete dominance occurs when

One allele masks the effect of another

Codominance occurs when

More than one allele is fully expressed

Incomplete dominance occurs when

Heterozygotes have an intermediate phenotype

Penetrance

Proportion of individuals with a given genotype who express the phenotype

Expressivity

Varying phenotypic manifestations of a given genotype

Mendel’s first law (of segregation) states

Organisms have two alleles for each gene, which segregate during meiosis

Mendel’s second law (of independent assortment) states

Inheritance of one allele does not influence inheritance of another

Griffith experiment demonstrated

The transforming principle converting nonvirulent bacteria to virulent bacteria

Avery–MacLeod–McCarty experiment demonstrated

DNA is genetic material because degradation of DNA stops transformation

Hershey–Chase experiment confirmed

DNA is the genetic material because only radiolabeled DNA entered bacteria

Silent mutation

No effect on protein

Missense mutation

Substitutes one amino acid for another

Insertions and deletions result in

Changes for all downstream amino acids (frameshift)

Chromosomal deletion mutation

Large segment of DNA is lost

Chromosomal inversion mutation

Segment of DNA reversed

Chromosomal duplication mutation

Segment of DNA copied multiple times

Chromosomal translocation mutation

Segment swapped between chromosomes

Genetic leakage

Flow of genes between species through hybrid offspring

True or False: Evolution acts on populations, not individuals.

True

Natural selection theory was first proposed by

Charles Darwin

Key requirement for natural selection

Variation in traits must be heritable

Favorable variation

A trait that increases reproductive success

Differential reproduction

Traits that increase reproductive success are passed on more

Modern synthesis model adds

Knowledge of genes, mutation, and recombination to Darwin’s theory

Punctuated equilibrium

Evolution occurs in rapid bursts separated by long periods of stability

Altruism explained by

Inclusive fitness

Example of directional selection

Antibiotic resistance in bacteria

Example of stabilizing selection

Human birth weight

Example of disruptive selection

Galapagos finch beak sizes

Polymorphisms

Naturally occurring differences in a population

Niche definition

Specific environment, including habitat, resources, and predators

Phenotypic ratio for a monohybrid cross (heterozygote × heterozygote)

3:1

Phenotypic ratio for a dihybrid cross (heterozygote × heterozygote)

9:3:3:1

Hemophilia is an example of

X-linked recessive disorder

A carrier female for an X-linked disorder

XhX

Punnett square: carrier female × normal male results in

50% carrier daughters, 50% normal sons

Punnett square: carrier female × affected male results in

25% affected daughters, 25% normal daughters, 25% affected sons, 25% normal sons

Genes very close on the chromosome are

Tightly linked

Genes far apart on the chromosome are

Weakly linked

1 centimorgan (cM)

1% recombination frequency

Two genes 25 cM apart

25% gametes expected to show recombination

Recombination frequency of 50%

Genes assort independently

Order of genes can be deduced by

Adding recombination frequencies (map units)

Allele frequency (dominant + recessive)

p + q

Frequency of heterozygous genotype

2pq

Frequency of homozygous recessive

q²

Frequency of homozygous dominant

p²

Hardy–Weinberg equilibrium shows

Allele frequencies remain constant over generations

If 9% of population is homozygous dominant, p²

?

Then p

?

Then q

?

Heterozygous frequency

2pq

Homozygous recessive frequency

q²

Dominant phenotype frequency

p² + 2pq

Prezygotic isolation prevents

Zygote formation

Postzygotic isolation results in

Sterile or nonviable offspring

Temporal isolation

Different breeding times

Ecological isolation

Different habitats

Behavioral isolation

Differences in mating behaviors

Reproductive isolation

Anatomical incompatibility