Bio 204 - Lecture - 10/20/11 Test

Front 1

Independent assortment does not have an effect on two genes on the same chromosome. However, ______ ______ can result in the two genes getting separated.

Back 1

crossing over

Front 2

frequency of crossing over:

Back 2

at least once every meiotic division for each chromosome

Front 3

Linkage map -

Back 3

Made by looking at the frequency of recombination of alleles of a gene in offspring.

Front 4

Complications to medelian genetics –

Back 4

1) Traits with multiple alleles, 2) polymorphic traits, 3) Codominance, 4) Pleiotropy, 5) Physical Environments Impact Genes, 6) Genetic Environment: impacts phenotypes, 7) Quantitative Traits

Front 5

Multiple alleles –

Back 5

when there are more than 2 alleles for the same gene

Front 6

Polymorphic traits -

Back 6

When more than two distinct phenotypes are present in a population due to multiple allelism

Front 7

Incomplete dominance -

Back 7

Neither allele is completely dominant over the other. Result: heterozygous offspring have intermediate phenotype to parental phenotypes

Front 8

Codominance –

Back 8

here the homozygous recessive and homozygous dominant appear together in separate phenotypes.

Front 9

Pleiotropy -

Back 9

a gene that affects more than one phenotype

Front 10

Physical Environments Impact Genes -

Back 10

Phenotypes produced by most allele combinations are impacted by an individual’s environment

Front 11

Genetic Environment:

Back 11

impacts phenotypes. Example: comb shape depends on two genes that interact ( R & P ). The phenotype produced depends on the alleles present for the other gene.

Front 12

Quantitative Traits –

Back 12

Phenotypes that produced by multiple genes. Phenotypic histograms of traits in a population with quantitative genes often result in a normal bell curve

Front 13

The Modern Synthesis

Back 13

(of evolution and genetics) combines Darwin’s ideas with those of researchers after him. Focuses on how evolution works at the level of genes, phenotypes, and populations.

Front 14

Three aspects of the modern synthesis

Back 14

1) There are several mechanisms of evolution in addition to natural selections.
2) Traits are inherited as discrete entities called genes. Variation within a population is due to the presence of multiple alleles of a gene
3) Speciation is due to the gradual accumulation of small genetic changes.
Evolution Change in allele population over time
Population localized group of individuals that are capable of interbreeding and production fertile offspring.
Gene pool the total set of alleles in a population at any one time.
Evolution depends on hereditable differences, not difference due to environment (short grass on the dry side of the meadows)
Hardy-Weinberg Principle: analyzing change in allele frequency: What happens to the frequency of alleles when many individuals in a population mate and produce offspring
-G. H. Hard and Weinberg imagined the world a giant pool of alleles bumping into each other
- Assumed that gene pools are inherently stable over time. Frequencies of alleles and genotypes in a population’s gene pool…which directly contradicts evolution
- H-W Assumptions:
i) Two alleles of a single gene: A1 and A2 (A a), p= frequency of A1 alleles in gene pool (A), q= frequency of A2 alleles in gene pool (a). p+q=1
p^2 + 2pq + q^2=1.
1) Assumes there is no selection (natural or artificial
2) Assumes no genetic drift (very large population size, no sampling effect, no random change, in allele freq.)
3) Assumes no migration
4) Assumes no mutations
5) Assumes random mating with respect to the gene in question

Front 15

Directional selection

Back 15

An area is selected against and the normal distribution shifts, tends to reduce genetic diversity within populations but only if selection pressure is constant (not yearly variation) and no strong counterbalancing selection pressures

Front 16

Stabilizing selection

Back 16

no change in average value of trait, but a decrease in variation (due to low fitness of the outliers on both sides)

Front 17

Disruptive/Diversiying selection

Back 17

happens when the outliers on each side have higher fitness than the average. Can result in balances polymorphism or speciation

Front 18

Genetic drift –

Back 18

change in allele frequency due to random events. Biggest impact is on a small population.

Front 19

Fixation –

Back 19

allele ratio becoming 1. As in the only allele option in the population

Front 20

Bottleneck Event –

Back 20

large population drastically reduced in size by chance without regard for fitnesss. By chance, some of the survivor’s alleles may be over or under represented.

Front 21

Founding event –

Back 21

New population starts with a few individuals not genetically representative of a larger source population.