BIOL 1111 Chapter Notes - Chapter 18: Genotype Frequency, Allele Frequency, Heterozygote Advantage

You begin work on the genetics of shell banding patterns in a snail. A test cross indicates that mottling is controlled by two alleles (M and m) at a single locus. Individuals carrying the M allele have mottled shells, while mm snails have no mottling. You sample a population and determine that the frequency of m in the population is 0.6. Assume that the population is at HWE when answering the following questions: (i) What is the frequency of the M allele in the population? (ii) What are the expected genotype frequencies in the next generation? (iii) What are the expected frequencies of the mottled and non-mottled phenotypes in the next generation? (iv) How should the frequency of the M allele change through time

Part A

In humans, individuals may or may not have a widow’s peak. This trait is controlled by genes at a single locus, with the allele for having a widow’s peak dominant to the allele for not having one. A population of humans is sampled; 59 have a widow’s peak and 44 do not. 25 of the people with a widow’s peak are homozygous dominant. What are the frequencies of the dominant and recessive alleles observed in this sample?

p = _____

q = _____

Part B

In a species of corn, individuals have either narrow or wide corn cobs. This trait is controlled by genes at a single locus, with the narrow cob allele dominant to the wide cob allele. A farmer counts 74 narrow cob and 113 wide cob plants in a field. Of the narrow cob plants, 28 are homozygous dominant. What are the frequencies of the dominant and recessive alleles observed in this sample?

p = _____

q = _____

Part C

In a population of peas, the frequency of the dominant allele for a purple flower is 0.61 and the frequency of the recessive allele for a white flower is 0.39. What would the genotypic frequencies be if the population is in equilibrium?

_____ = Frequency of homozygous dominant individuals

_____ = Frequency of heterozygous individuals

_____ = Frequency of homozygous recessive individuals

How many individuals would you expect of each genotype in a population of 500 peas?

_____ = Number of homozygous dominant individuals

_____ = Number of heterozygous individuals

_____ = Number of homozygous recessive individuals

Part D

In mice, a mahogany coat color allele is dominant over the tan coat color allele. In a population of mice, the frequency of the allele for mahogany coat color is 0.19 and the frequency of the allele for tan coat color is 0.81. What would the genotypic frequencies be if the population is in equilibrium?

_____ = Frequency of homozygous dominant individuals

_____ = Frequency of heterozygous individuals

_____ = Frequency of homozygous recessive individuals

How many individuals would you expect of each genotype in a population of 100 mice?

_____ = Number of homozygous dominant individuals

_____ = Number of heterozygous individuals

_____ = Number of homozygous recessive individuals

Part E

In humans, the free earlobe allele is dominant over the attached ear lobe allele. In a population of humans, the frequency of the allele for free earlobes is 0.42 and the frequency of the allele for attached earlobes is 0.58. What would the genotypic frequencies be if the population is in equilibrium?

_____ = Frequency of homozygous dominant individuals

_____ = Frequency of heterozygous individuals

_____ = Frequency of homozygous recessive individuals

How many individuals would you expect of each genotype in a population of 25 humans?

_____ = Number of homozygous dominant individuals

_____ = Number of heterozygous individuals

_____ = Number of homozygous recessive individuals

Evolution is change over ____________. Why is evolution an important concept in biology?

What is a population? How can you identify a population in nature?

What is the ultimate source of random variation in a population? Is this the only source of variation, why or why not?

What is a gene pool? Why is it important to our study of evolution?

How is variation inherited in a population? HINT: There are at least two main contributors to this variation. You should be focusing on gametes!

What is microevolution versus macroevolution?

How do the peppered moths show us microevolution in nature? Why is this NOT macroevolution? HINT: you should consider alleles and mating in your answer.

Do you believe that the Hardy-Weinberg equilibrium is common in nature? Why or why not? In your answer, you should incorporate your knowledge of populations, evolution, and genetics.

Evolution is driven by adaptation and natural selection. In populations, we refer to organisms that are “most fit.” Explain how evolution and the environment would result in organisms that are “most fit.” In your answer, indicate whether the “most fit” organism today is likely to be the “most fit” organism in the future and why.

Microevolution is a change in the frequency of ___________________ in a population but has not resulted in a speciation event thus far. Given this, what factors could lead to a speciation event for this population?

How would you know that a population had divided into two different species (macroevolution)? How could you test for a speciation event experimentally?