Ch 12: Genetics & Evolution (13%)

genes

Chromosomes contain ______ in a linear sequence

alleles

alternative forms of a gene

genotype

the combination of alleles one has at a given genetic locus (location on a specific chromosome)

hemizygous

when one has only one allele for a gene (such as in male sex chromosomes)

complete dominance

Patterns of Dominance

occurs when the effect of one allele completely masks the effect of another; the presence of one dominant allele will mask the recessive allele, if present

codominance

Patterns of Dominance

occurs when there is more than one dominant allele; ex: people with one allele for the A blood antigen and one allele for the B blood antigen, expressing both antigens simultaneously as the AB blood type

incomplete dominance

Patterns of Dominance

occurs when there are no dominant alleles; heterozygotes have intermediate phenotypes; ex: a red and white flower making pink flowers

penetrance

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

expressivity

refers to the varying phenotypic manifestations of the same genotype

population, individual

Penetrance works at the ______________ level while expressivity works at the ______________ level

Mendel’s First Law (Law of Segregation)

states that an organism has two alleles for each gene, which separate during meiosis, resulting in gametes carrying only one allele for a trait; demonstrated during anaphase I of meiosis

Mendel’s Second Law (Law of Independent Assortment)

states that the inheritance of one allele does not influence the probability of inheriting an allele for a different trait; demonstrated during prophase I of meiosis (recombination)

recombination

when 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 chromosome

epigenetics

changes in DNA that do not involve an alteration to the nucleotide sequence; can include the covalent attachment of different chemical groups to nucleotides and histone proteins

gene pool

all of the alleles in a given population

mutations

changes in DNA sequence

nucleotide mutations, chromosomal mutations

Mutations

name the 2 classes of mutations

point mutations, frameshift mutations

Mutations

name the 2 types of nucleotide mutations

point mutations

Mutations

the substituting of one nucleotide for another; type of nucleotide mutation

frameshift mutations

Mutations

moving the 3-letter transcriptional reading frame; type of nucleotide mutation

silent

Mutations

nucleotide mutations that have no effect on the final protein synthesized from the gene

missense

Mutations

nucleotide mutations that result in the substitution of one amino acid for another in the final protein

nonsense

Mutations

nucleotide mutations that result in the substitution of a stop codon for an amino acid in the final protein (an early stop codon)

insertions, deletions

Mutations

nucleotide mutations that result in a shift in the reading frame, leading to changes for all downstream amino acids (2)

deletions

Mutations

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

duplications

Mutations

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

inversions

Mutations

chromosomal mutations that occur when a segment of DNA is reversed within the genome

insertions

Mutations

chromosomal mutations that occur when a segment of DNA is moved from one chromosome to another

translocations

Mutations

chromosomal mutations that occur when a segment of DNA is swapped with a segment of DNA from another chromosome

inborn errors of metabolism

Mutations

a class of deleterious mutations characterized by deficiencies in genes required for metabolism; children born with these deficient genes often require very early intervention in order to prevent permanent damage from the buildup of metabolites in various pathways; ex: phenylketonuria (PKU)

genetic leakage

the flow of genes between species through hybrid offspring

genetic drift

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

founder effect

a more extreme case of genetic drift that results from bottlenecks that suddenly isolate a small population, leading to inbreeding and increased prevalence of certain homozygous genotypes

monohybrid cross

a cross that accounts for one gene (ex: Pp x Pp)

dihybrid cross

a cross that accounts for two genes (ex: TtPp x TTpp)

sex-linked cross

crosses wherein sex chromosomes are usually used to indicate sex as well as genotype (ex: X_hX x X_hY)

recombination frequency

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

Hardy-Weinberg Principle (population is in Hardy-Weinberg equilibrium)

states that if a population meets certain criteria indicative of a population with a stable gene pool and a lack of evolution, then the allele frequencies will remain constant

allele frequency

how often an allele appears in a population

p + q = 1 (frequency of dominant allele + frequency of recessive allele = 1)

write out for Hardy-Weinberg formula for finding the frequency of alleles in a population

p² + 2pq + q² = 1 (frequency of homozygous dominant genotype + frequency of heterozygous dominant genotype + frequency of homozygous recessive genotype = 1)

write out the Hardy-Weinberg formula for finding the frequency of genotypes and phenotypes in a population

natural selection

states that chance variations exist between individuals and that advantageous variations (those that increase an individual’s fitness) afford the most opportunities for reproductive success

populations, individuals

______________ evolve, not ______________

mutation, recombination, differential reproduction

The modern synthesis model (neo-Darwinism) accounts for __________ and ______________ as mechanisms of variation and considers ______________ _____________ to be the mechanism for reproductive success.

inclusive fitness

a measure of an organism’s success in a population based on the number of offspring, success in supporting offspring, and the ability of the offspring to then support others; survival of offspring or relatives ensures appearance of genes in subsequent generations

theory of punctuated equilibrium

considers evolution to be a very slow process with intermittent rapid bursts of evolutionary activity

Phenotypes

Different types of selection lead to changes in _____________

stabilizing selection

Types of Selection

keeps phenotypes in a narrow range, excluding extremes

directional selection

Types of Selection

moves the average phenotype towards one extreme

disruptive selection

Types of Selection

moves the population toward two different phenotypes at the extreme; can lead to speciation

adaptive radiation

Types of Selection

the rapid emergence of multiple species from a common ancestor, each of which occupies its own ecological niche

species

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

speciation

the formation of a new species through evolution

divergent evolution

Types of Evolution

occurs when two species sharing a common ancestor become more different

parallel evolution

Types of Evolution

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

convergent evolution

Types of Evolution

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

molecular clock model

states that 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