Lecture #12 - Evolution Flashcards
“Ctenophora-sister” hypothesis
implies that eumetazoan-specific traits either evolved once along the metazoan stem lineage and became lost in sponges and placozoans, or evolved at least twice independently in ctenophoroa and in cnidaria and bilateria
Gene linkage
closer they are, more often they are inherited together because recombination depends on distance
is the mitochondrial linked?
yes it is 100% linked because there is NO recombination
Cambrian Explosion
the sudden appearance in the fossil record of complex animals w/ mineralized skeletal remains; 542 mya
evolution
change w/ time; occurs through natural selection and neutral processes
Evolutionary fitness
the number of viable offspring an individual has
Evolution by natural selection requires
heritable variation that impacts evolutionary fitness
Steps of selection:
- Genetic variability that affects a trait exists in a population
- Environmental factors favor survival of individuals w/ some heritable traits over others → adaptive heritable traits
- Heritable adaptive traits may lead to differential reproduction, allowing individuals w/ the adaptation to produce more offspring
mutations are
random DNA changes
mutations provide a source of
variation
mutations within what are inheritable?
gametes
Selection advantage
only effective if it is more than ½ Ne → larger than the inverse of 2x the population size
neutral processes
Populations can experience genetic “drift” in which they develop different genotypes over time
Neutral theory
great majority of substitutions are caused by random fixation by sampling of selectively equivalent alleles; suggests that adaptive differences are rare, not that they are totally absent
why does population size matter?
Small populations quickly lose the alternative allele and thus have less genetic variation
where do adaptive genes come from?
Likely coming from the standing genetic variation within a population (the variation that is already present)
most major taxonomic groups are old, BUT
the species in these groups can be relatively young
