IB Biology SL D4.1 Natural Selection Questions

Insect pollinators are vital to maintaining the biodiversity of ecosystems, but they are threatened by some human actions. Some pollinators, such as honey bees (Apis mellifera), produce honey, which is rich in glucose.

Explain how a plant species may evolve by natural selection over a long period to produce insect-pollinated flowers.

Explain how sexual reproduction can eventually lead to evolution in offspring.

Outline how overpopulation of a species in a given environment may lead to evolution.

PanI is a gene in cod fish that codes for an integral membrane protein called pantophysin. Two alleles of the gene, $\operatorname{PanI}{ }^{\mathrm{A}}$ and $\operatorname{PanI}{ }^{\mathrm{B}}$, code for versions of pantophysin, that differ by four amino acids in one region of the protein. Samples of cod fish were collected from 23 locations in the north Atlantic and were tested to find the proportions of PanI ${ }^{\mathrm{A}}$ and PanI ${ }^{\mathrm{B}}$ alleles in each population. The results are shown in pie charts, numbered 1-23, on the map below. The proportions of alleles in a population are called the allele frequencies. The frequency of an allele can vary from 0.0 to 1.0 . The light grey sectors of the pie charts show the allele frequency of PanI ${ }^{\mathrm{A}}$ and the black sectors show the allele frequency of PanI ${ }^{\mathrm{B}}$.

The sites close to Iceland, at a latitude of $60-65^{\circ}$, had very varied allele frequencies, with both PanI ${ }^{\mathrm{A}}$ and PanI ${ }^{\mathrm{B}}$ occurring. The water at these sample sites was highly stratified, with much warmer water at the surface and much colder water below. Suggest reasons for both $\operatorname{PanI}^{\mathrm{A}}$ and $\operatorname{PanI}^{\mathrm{B}}$ alleles occurring at these sites.

The sickle-cell hemoglobin allele $\left(\mathrm{Hb}^{\mathrm{s}}\right)$ has a high frequency in regions where there is malaria. This is believed to be due to a selective advantage against fatal malaria for the heterozygote ( $\mathrm{Hb}^{\mathrm{A}} \mathrm{Hb}^{\mathrm{s}}$ ). Individuals who are homozygous for the sickle cell allele ( $\mathrm{Hb}^{\mathrm{s}} \mathrm{Hb}^{\mathrm{s}}$ ) have sickle cell anemia while heterozygotes have a much less severe form of the disease. Normal individuals without sickle cell anemia are designated $\mathrm{Hb}^{\mathrm{A}} \mathrm{Hb}^{\mathrm{A}}$.

This study involved 1022 children living in an area of Kenya where malaria is present. The possible protective effect of the sickle cell allele against mortality due to malaria was investigated. The data show the percentage of children surviving after birth over a period of 48 months.

A central idea in the theory of evolution is that species may evolve gradually over time from a common ancestor.

Which statement(s) explain(s) the pattern of evolution seen in the diagram?

I. Beak shape shows genetic variability in the common ancestor.
II. Changes in beak shape that occur during the lifetime of an individual bird are passed on to the next generation.
III. Changes in beak shape are heritable and make each species better adapted to its environment.

A bird of paradise (Ptiloris victoriae) has very showy plumage and demonstrates a unique dance.

What type of selection pressure could have caused this plumage to evolve?

John Endler's experiments modelled sexual and natural selection in Trinidadian guppies (Poecilia reticulata) by controlling selection pressures.

What did the experiments of John Endler demonstrate?