Lecture 9: Nonrandom Mating

Question 1

DEF: In nature, mating may not be random with respect to any particular gene,
– violate the Hardy-Weinberg assumption

Answer 1

Nonrandom Mating

includes:
- Inbreeding
- Assortative mating
- Sexual Selection

Question 2

DEF: mating between relatives

Answer 2

Inbreeding

Question 3

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

Answer 3

True

Question 4

Inbreeding Increases h______ and Decreases
______

Answer 4

Homozygosity, Heterozygosity

Question 5

Inbreeding does not cause e_____,
– Increases homozygosity
– Allele frequencies do not change in the population as a whole
– Changes genotype frequencies

Answer 5

Evolution

Question 6

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

Answer 6

Rate, deleterious

Question 7

Inbreeding d_____ is a decline in average
fitness that takes place when
– homozygosity i_______ and
– heterozygosity d______ in a population

Answer 7

Depression, increases, decreases

Question 8

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

Answer 8

Heterozygotes, Homozygous recessive

Question 9

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

Answer 9

Advantage

Question 10

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

Answer 10

True

Question 11

Another form of nonrandom mating is a_____ m_____.
- which is nonrandom with respect to specific traits

Answer 11

Assortative Mating

Question 12

Positive assortment:
- Individuals tend to choose mates that s____ a particular phenotypic trait with them.

Answer 12

Share

Question 13

Negative assortment:
- Individuals choose mates that d____ in a specific
phenotypic trait

Answer 13

Differ

Question 14

Another form of nonrandom mating is s____ s_____.
- which occurs when individuals within a
population differ in their ability to attract mates

Answer 14

Sexual Selection

Question 15

• Sexual selection favours individuals with h_____ traits that enhance their ability to obtain mates.

Answer 15

Heritable

Question 16

Does sexual selection lead to
changes in allele frequencies in a population and
increases fitness?

Answer 16

Yes

Question 17

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

Answer 17

True

Question 18

Sexual selection can take the form of
– I_____ selection, or mate choice
– I_____ selection, where individuals compete to
obtain mates

Answer 18

Intersexual, Intrasexual

Question 19

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

Answer 19

True

Question 20

DEF: Traits that attract the opposite sex are more
elaborate in males

Answer 20

Pattern

Question 21

DEF: Eggs are more energetically costly to create
than sperm

Answer 21

Process

Question 22

The f_______ a______ of s__ results from
the fact that, in most species, females invest more
in their offspring than do males

Answer 22

Fundamental asymmetry of sex

Question 23

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

Answer 23

Gain resources

Question 24

Male fitness is limited by the n____ of f____ he can mate with, and he can mate frequently because sperm are so energetically inexpensive

Answer 24

Number of females

Question 25

The Bateman–Trivers hypothesis of sexual
selection predicts:

• Females, but not males, should be choosy about mates since they invest a lot in each egg. The opposite should be true for males
  – Males will compete with each other for mates
  – Alleles that increase a male’s attractiveness or success in male–male competition should increase in
  population
  – Sexual selection should act more strongly on males
  than on females

T or F

Answer 25

True

Question 26

In several bird species, females prefer to mate
with healthy, well-fed males

Three key observations led to these experiments:
1. Existence of colourful feathers or beaks is due to the presence of pigments called c_______
2. Carotenoids protect tissues and help the immune
system fight disease
3. Animals must eat plants in order to obtain carotenoids

Answer 26

Carotenoids

Question 27

The healthiest birds should thus have the most colourful beaks and feathers
* Dull colouration occurs if birds must use their carotenoids to stimulate the immune system or if few carotenoids are available

Assumption: Father’s ability to fight off disease and feed efficiently is due to his “good alleles”
– Females that choose colourful males are more likely to have offspring with better disease-fighting and feeding abilities
* Experiments with zebra finches support the hypothesis that females prefer colourful (healthy, well-fed) males

T or F

Answer 27

True

Question 28

In many species, colourful markings and other types of courtship displays signal that males have good alleles.
* These honest signals of male genetic quality can also
– indicate males that care for young or
– that provide the resources for females
* Thus, females may choose males based on
– Their physical characteristics that signal male genetic quality
– Behavioural characteristics that indicate ability to provide parental care OR
– Both of these

T or F

Answer 28

True

Question 29

In other species, male–male competition is the
primary cause of sexual selection instead of mate
choice

T or F

Answer 29

True

Question 30

Example: Sexual selection is intense in elephant
seals and is driven by male–male competition
– Males compete to defend the few beaches with gentle slopes that females can use to give birth

T or F

Answer 30

True

Question 31

Male elephant seals establish t______, areas
that they defend and can use exclusively
* Males that win battles with other males
monopolize matings with females in their territory
– Fights are usually won by the larger male

Answer 31

Territories

Question 32

Male elephant seals are over four times larger
than females
– Dominant males father large number of offspring
– Males that lose fights father few or no offspring
▪ Thus, alleles from large successful males will increase in
frequency in the population
▪ If the ability to win fights and produce offspring is
determined by body size, then alleles for large body size
have a significant fitness advantage
▪ Therefore there is d_______ selection for large body size What type of selection?

Answer 32

Directional selection

Question 33

Scientists have followed elephant seals on one
island to examine lifetime reproductive success
* Sexual selection in male elephant seals is intense
– A few males sire most offspring while most males
father few or none
▪ thus, variation in reproductive success is high in m___
* F____ have lower variation in reproductive
success than there is in males

Answer 33

Males, Females

Question 34

S____ selected traits often differ sharply
between the sexes because
– Most females get a mate, but many males do not
– Thus, sexual selection is more intense in males than in
females
– Males tend to have more traits that function in
courtship or competition for mates

Answer 34

Sexually

Question 35

DEF: refers to any trait that differs
between males and females of the same species
- Weaponry
– Ornamentation and behaviour in courtship
– Body size

Answer 35

Sexual dimorphism