Chapter 12 Genetics and Evolution

Genes

DNA sequences that code for heritable traits that can be passed from one generation to the next

Chromosomes

genes and noncoding DNA organized to ensure all genetic material is passed to daughter cells in mitosis and meiosis

Alleles

alternative forms of genes

Genotype

genetic combination of individualp

Phenotype

observable traits

Homologues

two copies of each chromosome

Locus

location on specific chromosome

Homozygous

both alleles same for gene

Heterozygous

alleles different for gene

Hemizygous

only one allele present for gene

Complete Dominance

only one dominant and one recessive allele for gene

Codominance

more than one dominant allele masks recessive allele

Incomplete Dominance

heterozygote expresses phenotype that is intermediate between two homozygous genotypes

Penetrate

proportion of individuals in population carrying allele who express phenotype

Huntington’s Disease

repetitive sequence of huntingtin gene

Full Penetrance

individuals with over 40 sequence repeats that all show symptoms

High Penetrance

fewer sequence repeats, most but not all show symptoms

Reduced/Low/Non-Penetrance

even fewer sequence repeats

Expressivity

varying phenotypes despite identical phenotypes

Constant Expressivity

all individuals with genotype express same phenotype

Variable Expressivity

individuals with genotype may have different phenotypes

Mendel’s First Law

law of segregation

Mendel’s Second LAw

law of independent assortment

Transforming Principle

live nonvirulent bacteria acquired ability to form smooth capsules from dead bacteria

Gene Pool

alleles in species

Mutations

change in DNA sequence resulting in mutant allele

Wild-Type

normal/natural alleles

Mutagens

substances that can cause mutations

Transposons

can insert and remove self from genome (can disrupt gene)

Point Mutation

occur when one nucleotide in DNA (A, C, T, G) swapped

Types of Point Mutations

silent, missense, nonsense

Silent Mutation

occur when change in nucleotide has no effect on final protein synthesized form gene

Degeneracy (Wobble)

changed nucleotide transcribed to be third nucleotide in codon

Missense Mutations

occur when change in nucleotide results in substituting one amino acid for another in final protein

Nonsense Mutations

occur when change in nucleotide results in substituting stop codon for an amino acid in final protein

Frameshift Mutations

occur when nucleotides are inserted into or deleted from genome

Codons

three letter sequences; insertion or deletions affecting reading frame, causing change in sequence

Chromosomal Mutations

large segments of DNA are affected

Types of Chromosomal Mutations

deletion, duplication, incersion, insertion, translocation

Deletion

occur when large segment of DNA lost from chromosome

Duplication

occur when segment of DNA copies multiple times in genome

Inversion

occur when segment of DNA reversed within chromosome

Insertion

occur when segment of DNA moved from one chromosome to another

Translocation

occur when segment of DNA from one chromosome swapped with segment of DNA from another chromosome

Advantageous Mutation

allow organism to produce more offspring

Deleterious Mutation

change in DNA sequence causing person to be at risk of developing genetic disorder or disease

Inborn Errors of Metabolism

defects in genes required for metabolism

Phenylketonuria (PKU)

cause seizures, cerebral function impairment, learning disabilities, musty odor to bodily secretions

Leakage

flow of genes between species

Hybrid

individuals from different (closely related) species reproduce

Genetic Drift

changes in composition of gene pool due to chance

Founder Effect

small population in reproductive isolation from other populations due to natural barriers, catastrophic events or bottlenecking

Inbreeding

mating between two genetically related individuals

Inbreeding Depression

loss of genetic variation reduce fitness of population

Outbreeding/Outcrossing

introduction of unrelated individuals that could increase fitness

Biometric Techniques

punnet square, map chromosomes, Hardy-Weinberg Equilibrium

Punnet Square

predict relative genotypic and phenotypic frequencies from crossing two individuals

Monohybrid Cross

cross in which one trait is studied

Parent/P Generation

individuals being crossed

Filial/F Generation

offspring

Test Cross

used to determine unknown genotype by crossing with homozygous recessive

In a test cross if all are dominant phenotype, what is the likely genotype?

dominant

In a test cross, if there is a 1:1 distribution what is the genotype?

heterozygous

Dihybrid Cross

account for inheritance of two different genes

Chiasma

point of crossing over of genes

Recombination Frequency

likelihood two genes are separates from each other when crossing over

Genetic Map

represents the relative distance between genes on a chromosome

Map Unit/Centimorgan

1% chance of recombination occurring between two genes

Allele Frequency

how often an allele appears in a population

Equation for Frequency of Alleles

p + q = 1

Equation for Frequency of Genotypes and Phenotypes

p2 + 2pq + q2 = 1

P2

frequency of homozygous dominant genotype

2pq

frequency of heterozygous dominant genotype

Q2

frequency of homozygous recessive genotype

What equation gives the dominant genotype?

p2 + 2pq

Natural Selection

survival of the fittest

Neo-Darwinism

adds knowledge of genetic inheritance and changes in gene pool to Darwin’s original theory  

Differential Reproduction

mutation or recombination results in favorable change, more likely to pass on to future generations

Inclusive Fitness

measure of organisms success in population

Punctuated Equilibrium

changes in some species occur in rapid bursts rather than evenly over time

Stabilizing Selection

keeps phenotypes within specific range by selecting against extremes

Directional Selection

adaptive pressure can lead to emergence and dominance of initially extreme phenotype

Disruptive Selection

two extreme phenotypes are selected over the norm

Polymorphisms

naturally occurring differences form between members of same population

Polymorphism Example

light or dark organism

Adaptive Radiation

concept describing rise of a number of different species from common ancestor

Niche

specific environment, available resources, predators for which a species can be specifically adapted

Species

largest group of organisms capable of breeding to form fertile offspring

Speciation

formation of new species through evolution

Isolation

one species splits into different habitats and evolves differently

Prezygotic Mechanisms

prevent formation of zygote completely

Temporal isolation

breeding at different times

Ecological Isolation

live in different niches with same territory

Behavioral Isolation

lack of attraction between members of two species due to differences in pheromones

Reproductive Isolation

incompatibility of reproductive anatomy

Gametic Isolation

intercourse can occur, fertilization cannot

Postzygotic Mechanisms

allow for gamete fusion, yield either nonviable or sterile offspring

Hybrid Inviability

formation of zygote that cannot develop to term

Hybrid Sterility

forming hybrid offspring that cannot reproduce

Hybrid Breakdown

first-generation are viable and fertile, second-generation are inviable or infertile