Genetics and Evolution Flashcards
Homologues
Each human being possesses 2 copies of each chromosome, except for male sex chromosomes
locus
Location on a specific chromosome, where a gene is located –> locus of a particular gene is consistent among human beings.
Hemizygous
Describes a situation in which only one allele is present for a given gene, as is the case for parts of the X chromosome in males.
Complete dominance
When only one recessive and one dominant allele are present, the presence of one dominant allele will mask the recessive allele, if present.
Incomplete dominance
Occurs when a heterozygote expresses a phenotype that is intermediate between the 2 homozygous genotypes
Penetrance
The proportion of the population with a given genotype who actually express the phenotype
Expressivity
The different manifestations of the same genotype across the population
Constant expressivity
All individuals with a given genotype express the same phenotype.
Variable expressivity
Individuals with the same genotype may have different phenotypes
4 basic tenets of Mendel’s first law (of segregation)
1) Genes exist in alternative forms (alleles)
2) An organism has 2 alleles for each gene – one inherited from each parent
3) The 2 alleles segregate during meiosis, resulting in gametes that carry only one allele for any inherited trait
4) If 2 alleles of an organism are different, only one will be fully expressed and the other will be silent (codominance and incomplete dominance are exceptions to this rule).
Mendel’s second law (of independent assortment)
States that the inheritance of one gene does not affect the inheritance of another gene
Gene pool
All of the alleles that exist within a species.
Transposons
Can insert and remove themselves from the genome
Point mutations
Occur when one nucleotide in DNA is swapped for another
Silent mutations
Occur when the change in nucleotide has no effect on the final protein synthesized from the gene
Missense mutations
Occurs when the change in nucleotide results in substituting one amino acid for another in the final protein
Nonsense mutations
Occurs when the change in nucleotide results in substituting a stop codon for an amino acid in the final protein.
Frameshift mutations
Occur when nucleotides are inserted into or deleted from the genome
Chromosomal mutations
Larger-scale mutations in which large segments of DNA are affected
Inborn errors of metabolism
Defects in genes required for metabolism
Leakage
A flow of genes between species, e.g. when individuals from different (but closely related) species can mate to produce hybrid offspring.
Genetic drift
Refers to changes in the composition of the gene pool due to chance
Inbreeding depression
The loss of genetic variation may cause reduced fitness of the population
Outbreeding or outcrossing
The introduction of unrelated individuals into a breeding group
Punnett squares
Diagrams that predict the relative genotypic and phenotypic frequencies that will result from crossing 2 individuals.
Monohybrid
A cross in which only one trait is being studied
Crossing 2 heterozygotes for a trait with complete dominance results in what type of ratio of genotypes and of phenotypes
1:2:1 ratio of genotypes (homozygous dominant: heterozygous dominant: homozygous recessive)
AND
a 3:1 distribution of phenotypes (dominant:recessive)
Test cross/back cross
Used to determine an unknown genotype
Dihybrid cross: ratio in offspring for crossing 2 things that are heterozygous for 2 different traits
9:3:3:1
Recombination freqency
The likelihood that 2 alleles are separated from each other during crossing over
map unit or centimorgan
Corresponds to a 1 percent chance of recombination occurring between 2 genes
5 conditions required for a population to be in Hardy-Weinberg equilibrium
1) the population is very large (no genetic drift)
2) There are no mutations that affect the gene pool
3) Mating between individuals in the population is random (no sexual selection)
4) There is no migration of individuals into or out of the population
5) The genes in the population are all equally successful at being reproduced`
2 key Hardy-Weinberg equations
p + q = 1
p^2 + 2pq + q^2 = 1
p is the frequency of the dominant allele
q is the frequency of the recessive allele
Neo-darwinism
Adds knowledge of genetic inheritance and changes in gene pool to Darwin’s original theory: when mutation or recombination results in a change that is favorable to the organism’s reproductive succes, that change is more likely to pass on to the next generation
Natural selection
The theory that certain characteristics or traits possessed by individuals within a species may help those individuals have greater reproductive success.
Punctuated equilibrium
Theory that little evolution would occur within a lineage of related lifeforms for long periods of time, followed by an explosion in evolutionary change.
Adaptive radiation
A related concept that describes the rapid rise of a number of different species from a common ancestor.
Prezygotic mechanisms
Prevent formation of the zygote completely –> can cause speciation
Postzygotic mechanisms
Allows for gamete fusion but yield either nonviable or sterile offspring –> can cause speciation
Divergent evolution
Refers to the independent development of dissimialr characteristics in 2 or more lineages sharing a common ancestor
Parallel evolution
Refers to the process whereby related species evolve in similar ways for a long period of time in response to analagous environmental selection pressures
Convergent evolution
Refers to the independent development of similar characteristics in 2 or more lineages not sharing a recent common ancestor
Molecular clock model
The more similar the genomes, the more recently the 2 species separated from each other.
Molecular evolutionists correlate the degree of genomic similarity with the amount of time since 2 species split off from the same common ancestor.
