Evolution Lecture 4

Question 1

Relative Fitness and selection

Answer 1

The shorter girrfae is a trait that’s under greater selective pressure. The longer neck trait is conferring higher relative fitness, they have more children because they get more food, then they live longer than have more children.

Question 2

Polygenic inheritance

Answer 2

Phenotype influenced by several genes (alleles at several loci). Coat colour of mice. This is a smooth range of phenotypes, “quantitative charter,” we can measure it and it varies along a range.

Question 3

The modes of selection?

Answer 3

Directional, Stabilizing, and Disruptive.

Question 4

Directional selection

Answer 4

One end of distribution selected against. Classic response to a changing environment (e.g. pesticide/drug treatments; climate change etc.).

Question 5

Stabilizing Selection

Answer 5

Extreme phenotypes selected against, so the average is the average. Often due to different, opposing selective forces. Happens often over lots of time can move the average to the optimal that has the most fitness.

Question 6

Disputive Selection

Answer 6

Intermediate phenotypes selected against. Role in some speciation events. Even if natural grey mice go extinct, we still expect to see them because when white and black mate they have a good chance at getting grey, however it’s possible we won’t see that because they start to act like two different species.

Question 7

What giraffes have the highest fitness?

Answer 7

Emo then fabio then normal. Even tho emo don’t live as long.

Question 8

Sexual Selection

Answer 8

Effectively, a special case of natural selection. Competition for mating opportunities. Results in adaptations that increase mating success. But (sometimes) actually reduce survival. The two types are intra and inter.

Question 9

Intrasexual Selection

Answer 9

Competition within one sex (usually males) for mating opportunities. Fights occur and there is a winner and loser. You have armaments, which are adaptions that will make it more likely for you to win.

Question 10

Intersexual Selection

Answer 10

One sex (usually females) chooses mate from (competing members of) other sex. Ornaments are adaptions that make it more likely for you to get picked. Eg. peacocks

Question 11

Can adaptions be both ornaments and armaments?

Answer 11

Yes

Question 12

Sexual Dimorphism

Answer 12

Adaptation benefits only one sex, while both sexes would suffer any survival cost. When females and males look noticeably different from one another. Eg. The emo male doesn’t care what the female looks like. Sexual dimorphism can also evolve via ‘normal’ natural selection, females are bigger, because they defend the nest.

Question 13

How do preserve allelic variation?

Answer 13

Diploid ‘hides’ recessive alleles from selection when they are rare (natural selection is good at pushing down harmful alleles but not at getting rid of them). Natural Selection can sometimes favour allelic variation: “Balancing Selection.”

Question 14

Balancing Selection

Answer 14

Balancing selection is a form of natural selection that favors many different versions of a gene and can occur when heterozygotes for the gene have an advantage over homozygotes. Example are Heterozygote advantage and Frequency-dependent selection.

Question 15

Heterozygote advantage

Answer 15

Where people who are heterozygous have an advantage.

Question 16

Frequency-dependent selection

Answer 16

The fitness of a phenotype depends on how common it is in the population.

Question 17

An example of heterozygote advantage?

Answer 17

Sickle Cell anemia. It’s a single locus recessive genetic disease, cause by a point mutation where T to A. It lets to hydrophobic interactions between the sick cell disease hemoglobin proteins under low-oxygen conditions. So they bind to each other in a chain. Cell becomes distorted under low oxygen conditions they can then clump together and block the flow of blood. In heterozygotes they have some sickle cells but not enough to be the disease.

Question 18

Why is it heterozygote advantage?

Answer 18

Because the heterozygote provides protection against malaria. This is because the body destroys sickled red blood cells rapidly, killing the parasites they harbour. In regions where malaria is popular, heterozygotes are favoured.