Lecture 17 Flashcards
(25 cards)
what are gene homologs?
a gene inherited in two species from a common ancestor.
what are gene homologs the result of?
shared ancestary
what is an ortholog?
is one of two or more homologous genes separated by a speciation event
as species split, what does that mean in terms of mutations?
as species split, mutations accumulate independently
For an ortholog, do the two diverged genes unreckognizable?
for an ortholog, we can tell they are still the same gene, but was just split by speciation
Through time, multipule rounds of gene duplication can turn a single gene into what?
can turn a single gene into a gene family
What are paralogs?
homologous genes resulting from duplication events.
what is a genealogy?
a “phylogeny” tree but for the ancestory of a single gene
what is coaslesence time?
- the idea of the most recent common ancestor, but at the gene level.
- pick any two alleles from the current generation and trace their history back in time. looking at how many generations it took to find a common ancestor is their coalesence time
What does “coalesce” mean?
the process by which, looking back in time, any pair of alleles merges in a common ancestor. eventually all alleles will coalesce at some point in the past
What does the amount of time it takes for an allele to coalese depend on?
depends on drift and selection
Why do alleles take a longer time to coalesce in a larger population?
because drift is weaker
When can alleles take longer to coalesce?
when purifying selection is so strong or if there is little selection
What is the impact of positive selection on coalescence time?
positive selection can accelerate the rise in frequency of a beneficial allele, leading to a shorter coalescence time
is coalescnce time the same or different for different genes?
coalescence time varies for different genes
do gene trees always match species trees?
no
what can cause gene and species trees to not match?
- incomplete lineage
- if gene is evolving at different rates in different species
what is census size (N)?
number of individuals in a population
what is Effective size (Ne)?
the number of individuals in an ideal population (in which every individual reproduces) in which the rate of genetic drift would be the same as it is in the actual population
What is the relationship between census size (N) and effective size (Ne)?
census size is always larger than effect size, they are not equal
what is Ne (effective size) reduced by?
it is reduced by anything that causes variance in progeny production among individuals
why is Ne smaller than N
- biased sex ratios
- non random mating
- selection
- fluctuation in population size
what is the relationship between coalescence and Ne?
- colascnence is faster when Ne is smaller
- coalescence is slower when Ne is larger
what is genomics?
the study of the structure and function of the genome
