Lecture 12 Flashcards
Founder effect
occurs when a small group leaves home to find new settlements, causing a new colony with different allele frequencies
by chance, it may either lack some alleles or have high frequency of others
Non-random mating - preferentially choosing mates within a group causes excess of _____
homozygotes
Non-random mating - preferentially choosing mates outside a group causes excess of ______
heterozygotes
population bottlenecks
occurs when a large population is drastically reduced in size
Does the new population or large ancestral population have a much more restricted gene pool?
The new population
mutations
a major and continual source of genetic variation in populations
- can introduce new alleles
- can convert one allele to another
Mutation - harmful recessive alleles
mutations reintroduce harmful recessive alleles
harmful recessive alleles are maintained in heterozygotes
mutation - genetic load
genetic load is the collection of recessive deleterious alleles present in a population
directional selection
causes an allele to increase (or decrease) in frequency over time
two cases of natural selection
negative selection
positive selection
both lead to changes in allele frequencies
negative selection
reduces frequency of a deleterious trait
positive selection
increases frequency of an advantageous trait
balanced polymorphism
persistence of harmful recessive alleles due to heterozygotes with increased fitness
Heterozygote advantage
another word for balanced polymorphism
-have a reproductive advantage under certain conditions
what can directional selection cause?
a deficiency of heterozygotes
what can balancing selection cause?
excess of heterozygotes
sickle cell disease - what is glutamic acid substituted by?
the gene defect is a known mutation of a singe nucleotide (SNP) (A to T) of the beta-globin gene (exhibits balanced polymorphism), which results in glutamic acid being substituted by valine at position 7
sickle cell allele - negative selection
sickle cell allele causes the recessive cell anemia trait (when homozygous), and is therefore under negative selection
sickle cell allele - under positive selection
the sickle cell allele helps protect heterozygotes from malaria
when did the major groups of mammals first arise?
between 70 and 50 mya
what did the asteroid/comet impact 66MYA likely cause?
mass extinction at KT boudnary
Aegypotphitecus
- 30-40 MYA
- monkey-like animal (size of a cat)
- found in tropical forests of Africa, tree dweller
- possible ancestors of gibbons, apes, and humans
Dryopithecus
- 22-32 MYA
- oak ape
- found in SW and central Europe
- of of the first hominoids
- ancestor to apes and humans
- lived in trees but could walk
- size of a 7 year old, small brains, and pointed snout
molecular evolution
the study of evolution through comparison of:
- DNA and protein sequences
- chromosome banding
- genome structure
What do fewer DNA sequence changes indicate?
closer relation and more recent divergence
molecular clock
the rate of mutation (assuming that rate is constant) between two DNA sequences can be used as a clock to provide a relative measure of time since divergence from a common ancestor
human-chimp genome similarity
- proteins differ by 2 amino acids on average
- roughly 30% human proteins are identical in sequence to the chimp protein
- gene duplication (or delections) account for about 2.7% of genome differences
what makes us human
traits defining “humanness” may be rare
-keratin gene (affects hair coverage; expressed in chimps and gorillas; nonsense mutation in humans)
-speech - FOXP2 gene
hemoglobin genes (embryonic –> fetal versions of hemoglobin; longer fetal period, increased brain growth)
Where does human lineage specific (HLS) gene change occur?
in the human lineage but noe of the other great apes
-changes may be responsible for specifically human phenotypes.
what makes us different?
gene expression not the genome sequence
synteny
the correspondence of gene order preserved between two species
how many autosomes do great apes have
23
Hominin
- fossils from 4-19 MYA scarce
- 6 MYA hominin line split off from other apes
3 candidates for first hominin
1) Ardipithecus kadabba (from Ethiopia)
2) Sahelanthropus tchadensis (from Chad)
3) Orrorin tugenensis (from Kenya)
