concept check questions 14.3 a rooster with gray feathers is mated with a hen of the same phenotype....

Concept Check Questions

14.3A rooster with gray feathers is mated with a hen of the same phenotype. Among their offspring, 15 chicks are gray, 6 are black, and 8 are white. What is the simplest explanation for the inheritance of these colors in chickens? What phenotypes would you expect in the offspring resulting from a cross between a gray rooster and a black hen?


14.3

In humans, tall parents tend to have tall children, and short parents tend to have short children. Adult heights, however, vary in the population over a wide range, following a normal bell-shaped curve. Explain these observations.


14.4Beth and Tom each have a sibling with cystic fibrosis, but neither Beth nor Tom nor any of their parents have the disease. Calculate the probability that if this couple has a child, the child will have cystic fibrosis. What would be the probability if a test revealed that Tom is a carrier but Beth is not?


14.4Joan was born with six toes on each foot, a dominant trait called polydactyly. Two of her five siblings and her mother, but not her father, also have extra digits. What is Joan’s genotype for the number-of-digits character? Explain your answer. Use D and d to symbolize the alleles for this character.


15.1

Which of Mendel’s laws relates to the inheritance of alleles for a single character? Which law relates to the inheritance of alleles for two characters in a dihybrid cross? What is the physical basis of these laws?


15.2

When two genes are located on the same chromosome, what is the physical basis for the production of recombinant offspring in a test cross between a dihybrid parent and a double-mutant parent?


15.2

Genes A, B, and C are located on the same chromosome. Test crosses show that the recombinant frequency between A and B is 28% and between A and C is 12%. Can you determine the linear order of these genes?


15.3

Neither Tim nor Rhoda has Duchenne muscular dystrophy, but their firstborn son does have it. What is the probability that a second child of this couple will have the disease?


15.4

More common than completely polyploid animals are mosaic polyploids, animals that are diploid except for patches of polyploid cells. How might a mosaic tetraploid—an animal with some cells containing four sets of chromosomes—arise?


15.4

About 5% of individuals with Down syndrome have a chromosomal translocation in which one copy of chromosome 21 is attached to chromosome 14. How could this translocation in a parent’s gonad lead to Down syndrome in a child?


15.4

Explain how a male cat could have the tortoise shell phenotype.


15.5

Gene dosage, the number of active copies of a gene, is important to proper development. Identify and describe two processes that help establish the proper dosage of certain genes.


15.5Reciprocal crosses between two primrose varieties, A and B, produce the following results: A female x B male → offspring with all green (nonvariegated) leaves. B female x A male → offspring with spotted (variegated) leaves. Explain these results.


15.5

Mitochondrial genes are critical to the energy metabolism of cells, but mitochondrial disorders caused by mutations in these genes are usually not lethal. Why not?

concept check questions 14.3 a rooster with gray feathers is mated with a hen of the same phenotype....

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