Exam 4

Mutations Disturb HWE

• mutations mostly recessive or deleterious
• generate variability for selection, BUT HWE doesn't want allele frequency to change
• most potent are acted on by selection over time
• mutations not big enough to be evolutionary

Mutation Selection Balance

• allele produced as fast as it is removed
• recessive alleles: higher mutation rate and higher allele frequency, REMOVED BY SELECTION
• dominant lethal alleles: mutation can stay in population
• q=(sqrt*u/s*)
• eg: spinal muscular atrophy in mutation selection balance (autosomal recessive) ( s=0.9)
• eg: cystic fibrosis not in mutation selection balance maybe b/c HETEROZYGOTE SUPERIORITY (autosomal recessive) (s=1)

Migration

• alleles move between a population; so INCREASE genetic variation
• aka gene flow
• general effect: homogenize allele frequency in a population
• eg: Northern watersnake, Diamond back watersnake
• founder effect but NOT migration: island empty..new people come over and start life

Non- random Mating

• non random selection: WHO mates with WHOM
• organisms choose desirable traits for most fit mate
• TWO types: Assortative mating and inbreeding
• Assortative mating: based on (positive) similarity or (negative) dissimilarity
• Negative Assortative mating: MHC ( women on birth control choose wrong mate)
• Posiitive Assortative mating: Tall mate with tall
• NOT an evolutionary force

Sexual Selection

• Particular traits are generally more attractive to mates--WHO GETS TO MATE
• An aspect of natural selection, but DOESN'T necessarily INCREASE FITNESS
• based on phenotype
• more F alleles, M has > fitness
• more M alleles, F has > fitness
• acts on individual/ allele not population
• acts on investment for fitness : so more males for HUMANS ( sex ratio: 1.03:1)
• More males produced= higher infant mortality in males
• Increase child fitness decreases parent's fitness

Inbreeding Depression

• mechanism to avoid inbreeding
• animals live as a family and males have to leave as they mature
• different smelling mate
• high mortality rate occurs
• inbreeding: exposure of deleterious allele
• most extreme form: self-fertilization

Rare sex advantage leads to 1:1 Sex Ratio

• via frequency dependent selection (genes selected at LOW frequency and against at HIGH freq)
• Moms stressed conditions and skewed sex ratio
• Males must be large to be successful
• could deviate due to inbreeding and competition

Gametes to Sexual Reproduction/Sex deter.

• FEMALE reproduction limited by # of eggs/ pregnancies
• MALE reproduction limited by number of marks
• MOM DETERMINES GENDER: make X or Y chromos, where eggs burried, high testosterone
• DAD DETERMINES GENDER: make all X or Y chromos
• FEMALES: larger parental investment per gamete (promotes development)
• MALE: less parental investment per gamete ( genetic info)

Types of Sexual Selection

• sexual dimorphism: differences in male/ female physical traits of same species
• -- males larger and showier b/c have to compete and b/c lots of sperm
• female choice: mating based on resources, good qualities, or characteristics
• male competition:males compete for access to more females
• desirable individuals have more offspring
• natural selection and selection may work in same or opposite directions
• Male competition would beat female choice because males have greater chance at many offspring

Non Random Mating in HWE

• disrupts HWE and causes allele frequency change
• mating should be random in HWE