MCAT Biology - Genetics and Evolution

Gene

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

Genotype

genetic combination possessed by an individual

Phenotype

Manifestation of given genotype as observable trait

Homozygous

both alleles are the same for a given gene

Hemizygous

describes situation in which only one allele is present for a given gene

Complete dominance

one dominant and one recessive allele exist for a given gene, one dominant allele mask the recessive allele

Codominance

One dominant allele exists for a given gene

Incomplete dominance

heterozygote expresses a phenotype that is intermediate between the two homozygous genotypes

Penetrance

population measure defined as proportion of individuals in the population carrying the allele who actually express the phenotype

Expressivity

Varying phenotypes despite identical genotypes

Expressivity constant

All individuals with given genotype express the same phenotype

Expressivity variable

individual same genotype may have different fenotype

Mendels first law

Genes exist in alternative forms

An organism has two alleles for each gene, one inherited from each parent

The two alleles segrate during meiosis, resulting in gametes that carry only one allele for any inherited trait

If two allele of an organism are different, only one will be fully expressed and other will be silent

Mendels second law: Law of independent assortment

Inheritance one gene does not affect inheritance of another gene

Epigenetics

DNA that do not involve an alteration to the nucleotide sequence

Imprinting

epigenetic process in which gene expression is determined by contributing parent

Gene pool

All of the alleles that exist within a species

Mutation

Change in DNA sequence

Mutagen

Substances that can cause mutation

Transposons

Insert and remove themselves from the genome

Point mutation

When one nucleotide is swapped for another

Silent mutation

Change in nucleotide has no effect on the final protein synthesized from gene

Missense mutation

change in nucleotide result in substituting one amino acid for another in the final protein

Nonsense mutation

change in nucleotide results in substituting a stop codon for amino acid in final protein

Frameshift mutation

nucleotides inserted or deleted from genome

Chromosomal mutation

large scale mutations in which large segments of DNA are affected

Deletion Mutation

When a large segment of DNA is lost from chromosome

Duplication mutation

occur when segment of DNA is copied multiple times

Inversion mutation

occur when segment of DNA is reversed within the chromosome

Insertion Mutation

Occur when segment of DNA is moved one chromosome to another. Small insertion mutation are considered frameshift

Translocation Mutaitons

Occur when segment DNA from one chromosome is swaped with segment DNA from another

Advantageous mutation

positive selective advantage that may lalow the organism to produce fitter offspring

Inborn errors of metabolism

deficincies in genes required for metabolism

Genetic leakage

flow of gene between species

Genetic drift

change in composition of the gene pool due to chance

Founder effect

Extreme case of genetic drift in which small population of species finds itself in reproductive isolation from other population as result of natural barriers, catastrophic events that drastically and suddenly reduce size of population avalible for breeding

Inbreeding

mating between genetically related 9ndividuals

Inbreeding depression

loss of genetic variation may cause reduced fitness of the population

Outbreeding

introduction unrelated individual into a breeding group

Biometric techniques

quanitative approaches to biological data

Pedigree charts

diagrams show relationships between people within families and indicate the presence or absence of a trait of interest

Autosomal dominant

trait is encoded by dominant gene on autosomal chromosome

Autosomoal recessive

trait only expressed if an individual has two copies of recessive allele

X linked recessive

trait encoded by gene located on X chromosome

Mitochondrial inheritance

mutated allele is on mitochondrial DNA rather than nuclear DNA

Y linked

inheritance pattern where trait carried on Y chromosome

Punnett squares

diagrams predict the relative genotypic and phenotypic frequencies that will result from the crossing of two individuals

Monohybrid

A cross in which only one trait is being studied

P generation

individuals being crossed

F generation

offspring

Test cross

organism with unknown genotype is crossed with an organism known be homozygous recessive

Recombination frequency

the likelihood that two alleles are separated from each other during crossing over

Genetic map

represents the relative distance between genes on a chromosome can be constructed

Map unit

one percent chance of recombination occuring between two genes

Five criteria for Hardy Weinberg

The population is very large, there are no mutation affect gene pool, mating between individual in population is random, no migration of individuals into or out of hte population, the genes int eh population are equally suceessful at being reproduced

Natural selection

Certain characteristics of traits possessed by individuals within species may help those individuals have greater reproductive sucesses, thus passing on those traits to offspring

Modern Synthesis Model

When mutation or recombination results in a change that is favorable to organism reproductive sucess, the change more likely pass on to the next generation

Differential reproduction

Traits passed on by the more successful organisms will become ubiquitous in gene pool

Inclusive fiteness

Measure of an organisms success in supporting offspring and the ability of the offspring to then support others

Punctuated equilibrium

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

Stabilizing selection

keep phenotypes within a specific range by selecting against extremes

Directional selection

Dominance of the initally extreme phenotype

Disruptive selection

Two extreme phenotypes are seelcted over the norm

Polymorphism

naturally occuring differences in form between members of the same population

Adaptive radiation

related concept that describes the rapid rise of a number of different species from common ancestor

Niche

specific environment, including habitat, avalible resources and predators, for which a species is specifically adaptive

Species

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

Speciation

formation of a new species through evolution

Isolation

progeny of these populations could no longer freely interbreed

Prezygotic mechanisms

prevent formation of the zygotic completely

Postzygotic mechanism

allow for gamete fusion but yield either nonviable or sterile offspring

Divergent evolution

refers to independent developpment of dissimilar characteristics in two or more lineages sharing common ancestor

Parallel evolution

Refer to process whereby related species evolve in similar ways for a long period of time in response to analogous environmental selection pressures

Convergent evolution

refer to the independent development of similar characteristic in two or more lineages not sharing a recent common ancestor