Genetics and Evolution

Penetrance

proportion of individuals that carry an allele in a population that express the phenotype

Expressivity

varying phenotypes that have identical genotypes

4 basic tenets of Mendel’s First Law

1. genes exist in alternative forms (alleles)

2. organism has two alleles for each gene

3. Two alleles segregate during meiosis, gametes that carry only 1 allele

4. if two alleles are different, only 1 is expressed

Mendel’s Second Law

Law of Independent assortment

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

How is genetic diversity increased

segregation of chromosomes and independent assortment

gene pool

All of the alleles that exist within a species

What are the 3 Point mutations

Silent mutations - change has no effect on the final protein

Missense mutations - change causes substitution of amino acids

Nonsense mutations - Change results in a Stop Codon

What are point mutations

When a single nucleotide is changed for another

Frameshift mutation

Nucleotides are inserted or deleted from the genome

Chromosomal mutations

Large-scale mutations of DNA segments

Deletion Mutation

Large segment of DNA is lost from chromosome

Duplication mutation

Segment of DNA is copied multiple times in the genome

Inversion mutation

Segment of DNA is reversed

Insertion mutation

segment of DNA is moved from one chromosome to another

Translocation mutation

DNA segment is swapped with another DNA segment from another chromosome

Genetic Leakage

Flow of genes within a species

Causes for decrease in genetic diversity

genetic drift, founder’s effect, inbreeding

Ratio of offspring for monohybrid crossing of two heterozygotes

Genotype - 1:2:1

Phenotype - 3:1

Ratio of offspring for dihybrid crossing of heterozygotes

9:3:3:1

Criteria for stable gene pool and no evolution

1. Population is very large (no genetic drift)

2. There are no mutations that effect gene pool

3. Mating between individuals is random

4. There is no migration of individuals in or out

5. the genes in the population are equally successful in being reproduced

Hardy-Weinberg equation

p + q = 1 (frequency of alleles)

p² + 2pq + q^{2 ₌} 1 (frequency of genotype and phenotype)

Differential reproduction

mutations or recombination have the ability to change an organism’s reproductive success and it can be passed on, good or bad

Types of Natural selection

1. Stabilizing selection

2. Directional selection

3. Disruptive selection

Stabilizing selection

Keeps phenotype within a specific range by selecting against extremes

Directional Selection

adaptive pressure causes the emergence and dominance of an extreme phenotype

Disruptive Selection

Two extreme phenotypes are chosen over the norm

Divergent Evolution

Independent development of dissimilar characteristics in two or more lineages sharing a common ancestor

Ex) cats and seals are both mammals in the order Carnivora

Parallel Evolution

Related species evolve in similar ways for a long period of time due to same environmental pressures

Convergent Evolution

independent development of similar characteristics in two or more lineages not sharing a common ancestor

Ex) Fish and dolphins

Rate of evolution

rate of change of a genotype over a period of time and is related to the severity of the evolutionary pressures (environment)