Lecture 9: Nonrandom Mating Flashcards
DEF: In nature, mating may not be random with respect to any particular gene,
– violate the Hardy-Weinberg assumption
Nonrandom Mating
includes:
- Inbreeding
- Assortative mating
- Sexual Selection
DEF: mating between relatives
Inbreeding
Inbreeding explained:
Relatives that inbreed are likely to share alleles they
inherited from their common ancestor
* The most extreme form of inbreeding is self-fertilization, or
selfing (or self-pollination in plants)
– Can occur when individuals have both male and female
reproductive organs
* Homozygous parents that self-fertilize produce all
homozygous offspring
* Heterozygous parents that self-fertilize produce
homozygous and heterozygous offspring in a 1:2:1 ratio
T or F
True
Inbreeding Increases h______ and Decreases
______
Homozygosity, Heterozygosity
Inbreeding does not cause e_____,
– Increases homozygosity
– Allele frequencies do not change in the population as a whole
– Changes genotype frequencies
Evolution
Inbreeding can speed the r___ of evolutionary change by increasing the rate at which natural selection eliminates recessive d_____ alleles (i.e., that lower fitness) from a population
Rate, deleterious
Inbreeding d_____ is a decline in average
fitness that takes place when
– homozygosity i_______ and
– heterozygosity d______ in a population
Depression, increases, decreases
Many recessive alleles represent loss-of-function
mutations
▪ Normally homozygous recessive individuals are rare in a population
▪ Most loss-of-function alleles exist in h______,
where they have little or no effect
▪ Inbreeding increases the frequency of h______
r_______ individuals
– Result: higher frequency of individuals expressing the mutation
Heterozygotes, Homozygous recessive
Many genes—especially those involved in fighting
disease are under intense selection for heterozygote
a_______.
- If an individual is homozygous at these genes, fitness declines
Advantage
Inbred offspring are expected to have lower
fitness than outcrossed offspring.
* This prediction has been verified in many species
– Panther offspring had decreased fitness when both
parents were from Florida compared to those who had
one parent from Florida and one from Texas
– Among humans, children of first-cousin marriages have
higher mortality rate than those from marriages
between nonrelatives
T or F
True
Another form of nonrandom mating is a_____ m_____.
- which is nonrandom with respect to specific traits
Assortative Mating
Positive assortment:
- Individuals tend to choose mates that s____ a particular phenotypic trait with them.
Share
Negative assortment:
- Individuals choose mates that d____ in a specific
phenotypic trait
Differ
Another form of nonrandom mating is s____ s_____.
- which occurs when individuals within a
population differ in their ability to attract mates
Sexual Selection
- Sexual selection favours individuals with h_____ traits that enhance their ability to obtain mates.
Heritable
Does sexual selection lead to
changes in allele frequencies in a population and
increases fitness?
Yes
Darwin first recognized that selection based on
courtship success is a mechanism of evolutionary
change
Darwin was initially perplexed by traits that seemed
maladaptive, such as long iridescent tails of peacocks
– Seemed maladaptive to spend energy to produce a
structure that would increase vulnerability to predation
– Concluded that must be adaptive to help the peacock
attract mates, resulting in increased reproductive success
T or F
True
Sexual selection can take the form of
– I_____ selection, or mate choice
– I_____ selection, where individuals compete to
obtain mates
Intersexual, Intrasexual
A. J. Bateman and Robert Trivers questioned why
extravagant traits were found in peacock males
but not females
The BATEMAN-TRIVERS hypothesis has an observed
pattern and a hypothesized process
T or F
True
DEF: Traits that attract the opposite sex are more
elaborate in males
Pattern
DEF: Eggs are more energetically costly to create
than sperm
Process
The f_______ a______ of s__ results from
the fact that, in most species, females invest more
in their offspring than do males
Fundamental asymmetry of sex
Female fitness is limited by the ability to g____ r____ needed to produce more eggs and healthier offspring, so females produce relatively few offspring during lifetime
Gain resources
Male fitness is limited by the n____ of f____ he can mate with, and he can mate frequently because sperm are so energetically inexpensive
Number of females