Page 48 - Genetics_From_Genes_to_Genomes_6th_FULL_Part1

40 Chapter 2 Mendel’s Principles of Heredity

mother lacked the dimple. What proportion of their 14. If you roll a die (singular of dice), what is the prob-
children would be expected to have a chin dimple? ability you will roll: (a) a 6? (b) an even number?
b. A man with a chin dimple and a woman who lacks (c) a number divisible by 3? (d) If you roll a pair of
the dimple produce a child who lacks a dimple. dice, what is the probability that you will roll two
What is the man’s genotype? 6s? (e) an even number on one and an odd number
c. A man with a chin dimple and a nondimpled on the other? (f) matching numbers? (g) two num-
bers both over 4?
woman produce eight children, all having the chin
dimple. Can you be certain of the man’s genotype? 15. In a standard deck of playing cards, four suits exist
Why or why not? What genotype is more likely, (red suits = hearts and diamonds, black suits =
and why? spades and clubs). Each suit has 13 cards: Ace (A),
11. Some inbred strains of the weedy plant Arabidopsis 2, 3, 4, 5, 6, 7, 8, 9, 10, and the face cards Jack (J),
thaliana flower early in the growing season, but other Queen (Q), and King (K). In a single draw, what is
strains flower at later times. Four different Arabdiposis the probability that you will draw a face card? A red
plants (1–4) were crossed, and the resulting progeny card? A red face card?
were tabulated as follows: 16. How many genetically different eggs could be formed
by women with the following genotypes?
Mating Progeny
1 × 2 77 late : 81 early a. Aa bb CC DD
1 × 3 134 late b. AA Bb Cc dd
1 × 4 93 late : 32 early c. Aa Bb cc Dd
2 × 3 111 late d. Aa Bb Cc Dd
2 × 4 65 late : 61 early
17. What is the probability of producing a child that will
3 × 4 126 late
phenotypically resemble either one of the two parents
a. Explain the genetic basis for the difference in flow- in the following four crosses? How many phenotypi-
ering time. How do you know that among this cally different kinds of progeny could potentially
group of plants, the flowering time trait is influ- result from each of the four crosses?
enced by the action of a single gene? Which allele a. Aa Bb Cc Dd × aa bb cc dd
is dominant and which recessive? b. aa bb cc dd × AA BB CC DD
b. Ascribe genotypes to the four plants. c. Aa Bb Cc Dd × Aa Bb Cc Dd
c. What kinds of progeny would you expect if you al- d. aa bb cc dd × aa bb cc dd
lowed plants 1–4 to self-fertilize, and in what ratios?
12. Among Native Americans, two types of earwax (ceru- 18. A mouse sperm of genotype a B C D E fertilizes an
men) are seen, dry and sticky. A geneticist studied the egg of genotype a b c D e. What are all the possibili-
inheritance of this trait by observing the types of off- ties for the genotypes of (a) the zygote and (b) a
spring produced by different kinds of matings. He sperm or egg produced by the mouse that develops
observed the following numbers: from this fertilization?
19. Your friend is pregnant with triplets. She thinks that it
Offspring is equally likely that she will be the mother of 3 sons,
Parents Number of mating pairs Sticky Dry 3 daughters, 2 sons and 1 daughter, or 1 son and 2
Sticky × sticky 10 32 6 daughters. Is she correct? Explain. (Assume that each
Sticky × dry 8 21 9 of the triplets is from a separate fertilization, and that
Dry × dry 12 0 42 boys and girls are equally likely.)

a. How is earwax type inherited? 20. Galactosemia is a recessive human disease that is
b. Why are no 3:1 or 1:1 ratios present in the data treatable by restricting lactose and glucose in the diet.
shown in the chart? Susan Smithers and her husband are both heterozy-
13. Imagine you have just purchased a black stallion of gous for the galactosemia gene.
unknown genotype. You mate him to a red mare, and a. Susan is pregnant with twins. If she has
she delivers twin foals, one red and one black. Can fraternal (nonidentical) twins, what is the
you tell from these results how color is inherited, as- probability both of the twins will be girls who
suming that alternative alleles of a single gene are in- have galactosemia?
volved? What crosses could you do to determine how b. If the twins are identical, what is the probability
color is inherited? that both will be girls and have galactosemia?