Page 47 - Genetics_From_Genes_to_Genomes_6th_FULL_Part1

Problems 39

PROBLEMS

Vocabulary b. Which of these phenotypes is controlled by the
1. For each of the terms in the left column, choose the dominant allele?
best matching phrase in the right column. c. A normal-colored female snake is involved in a
testcross. This cross produces 10 normal-colored
a. phenotype 1. having two identical alleles of a given gene
b. alleles 2. the allele expressed in the phenotype of and 11 albino offspring. What are the genotypes of
the heterozygote the parents and the offspring?
c. independent 3. alternate forms of a gene 5. Two short-haired cats mate and produce six short-
assortment haired and two long-haired kittens. What does this in-
d. gametes 4. observable characteristic formation suggest about how hair length is inherited?
e. gene 5. a cross between individuals both 6. Piebald spotting is a condition found in humans in
heterozygous for two genes
f. segregation 6. alleles of one gene separate into gametes which there are patches of skin that lack pigmenta-
randomly with respect to alleles of other tion. The condition results from the inability of
genes pigment-producing cells to migrate properly during
g. heterozygote 7. reproductive cells containing only one development. Two adults with piebald spotting have
copy of each gene one child who has this trait and a second child with
h. dominant 8. the allele that does not contribute to the normal skin pigmentation.
phenotype of the heterozygote a. Is the piebald spotting trait dominant or recessive?
i. F 1 9. the cross of an individual of ambiguous What information led you to this answer?
genotype with a homozygous recessive
individual b. What are the genotypes of the parents?
j. testcross 10. an individual with two different alleles 7. As a Drosophila research geneticist, you keep stocks
of a gene of flies of specific genotypes. You have a fly that has
k. genotype 11. the heritable entity that determines a normal wings (dominant phenotype). Flies with short
characteristic
l. recessive 12. the alleles an individual has wings are homozygous for a recessive allele of the
wing-length gene. You need to know if this fly with
m. dihybrid cross 13. the separation of the two alleles of a normal wings is pure-breeding or heterozygous for
gene into different gametes
n. homozygote 14. offspring of the P generation the wing-length trait. What cross would you do to
determine the genotype, and what results would you
Section 2.1 expect for each possible genotype?
2. During the millennia in which selective breeding was 8. A mutant cucumber plant has flowers that fail to open
practiced, why did breeders fail to uncover the princi- when mature. Crosses can be done with this plant by
ple that traits are governed by discrete units of inheri- manually opening and pollinating the flowers with
tance (that is, by genes)? pollen from another plant. When closed × open
3. Describe the characteristics of the garden pea that crosses were done, all the F 1 progeny were open. The
made it a good organism for Mendel’s analysis of the F 2 plants were 145 open and 59 closed. A cross of
basic principles of inheritance. Evaluate how easy or closed × F 1 gave 81 open and 77 closed. How is the
difficult it would be to make a similar study of inheri- closed trait inherited? What evidence led you to your
tance in humans by considering the same attributes conclusion?
you described for the pea. 9. In a particular population of mice, certain individuals
display a phenotype called short tail, which is inher-
Section 2.2 ited as a dominant trait. Some individuals display a
4. An albino corn snake is crossed with a normal-colored recessive trait called dilute, which affects coat color.
corn snake. The offspring are all normal-colored. Which of these traits would be easier to eliminate
When these first-generation progeny snakes are from the population by selective breeding? Why?
crossed among themselves, they produce 32 normal- 10. In humans, a dimple in the chin is a dominant charac-
colored snakes and 10 albino snakes. teristic controlled by a single gene.
a. How do you know that only a single gene is respon- a. A man who does not have a chin dimple has
sible for the color differences between these snakes? children with a woman with a chin dimple whose