Answers to chapter 23 "Structure your Knowledge" and Chapters 22 and 23 "Test your Knowledge"

Chapter 23 "Structure Your Knowledge"

1. a. The Hardy-Weinburg theorem states that allele frequencies within a population will remain constant from one generation to the next as log as only Mendelian segregation and sexual recombination of alleles are involved. This state requires five conditions: A large population, mating is random, mutation and migration are negligible and no selection pressure operates.

b. The main equation is P squared + 2 pq + Q squared = 1. In the Hardy-Weinburg equation, p and q refer to the frequencies of 2 alleles in the gene pool. The frequency of homozygous offspring are p x p or p squared, and q x q or q squared. Heterozygous individuals can be formed in two ways, depending on whether the sperm of the ovum carries the p or q allele, so their frequency is equal to 2pq. Also, since there are only two forms of the gene (in this equation), p + q= 1.

2. Genetic variation is retained within a population due to the presence of diploidy (2 copies of an allele per gene) and balancing selection. Diploidy masks recessive alleles from selection when they occur in the heterozygote. Thus, less adaptive or even harmful alleles are maintained in the gene pool, and are available should selection pressures change. Balanced selection maintains several alleles at a gene locus in a population and leads to balanced polymorphism. In situations where there is heterozygote advantage, the two alleles will be retained in stable frequencies within the gene pool. Frequency-dependent selection, in which varieties present in larger quantities are selected against by predators or other factors, is another cause of balanced polymorphism.


Answers to Chapter 22 "Test Your Knowledge:

1.b 2.c 3.e 4.a 5.c 6.a 7.e 8. d
9.d 10.d 11.c 12.e 13.b 14.(d) 15.c 16.c


Answers to Chapter 23 "Test Your Knowledge"
1.e 2.a 3.c 4.c 5.d 6.d 7.e 8.d
9.b 10.e 11.e 12.c 13.d 14.a 15.b 16.b
17.c 18.b 19.b 20.(c) 21.a 22 e 23 d 24.(c)
25.e