Genetic Variation Flashcards
What is a homologous trait?
A trait that is shared by two species because it was inherited from a common ancestor.
What is homoplasy?
A trait that is shared by two species without having a common recent ancestor.
What is convergent evolution? Give an example.
When organisms that are not closely related evolve similar traits because of their environment. An example is flight in birds and insects.
What are the three categories of variation among individuals in evolution?
Genetic - differences among individuals
that is encoded in the genome and transmitted
from parents to offspring. E.g. armor in sticklebacks
Environmental - environment determines phenotype E.g. temperature sex determination in geckos
Genotype by environment - how environment affects phenotype is heritable.
Are most mutations beneficial?
No, some can be and some can be neutral but most worsen genetic function.
What are the four different types of mutations?
Point mutations - addition/deletion/substitution of 1 or a few pairs of nucleotides
Gene duplication - often from unequal crossing over, changes the number of genetic elements
Chromosome mutations - fusions and fissions, deletion, duplication and inversions, chromosome number and structure is diverse and can evolve rapidly
Whole genome mutations - polyploidization, can occur within or between species
Where does genetic variation come from?
Mutation
Recombination (increases rate of variation): Sexual reproduction (independent segregation of non-homologous characters, crossing over of homologous chromosomes). Asexual reproduction: meiosis.
Gene flow
Why is genetic variation important in evolution?
Improves a species ability to survive and adapt to its environment. It allows natural selection on alleles to increase or decrease in frequency in a population.
What is aneuploidy?
If one chromosome in a diploid is represented by more than two copies.
Can mutation rates be affected by the environment? Explain.
Yes, environmental factors like heat, UV, chemical mutagens, etc. can affect mutation rates.
What are four mechanisms of gene rearrangement?
Inversions
Translocations
Fusion/fission
What is Hardy Weinberg equilibrium and its seven assumptions?
p^2 + 2pq + q^2 = 1
Assumptions:
- Organisms are diploid
- Only sexual reproduction occurs
- Generations are nonoverlapping
- Mating is random
- Population size is infinitely large
- Allele frequencies are equal in the sexes
- There is no migration, mutation or selection
What does recombination do for populations? Where does it come from?
Generates new combinations of existing alleles.
Independent assortment (genes on different chromosomes) and crossing over (genes on the same chromosomes)
What is crossing over?
The exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring.
