Hartl, Jones - Genetics. Principlers and analysis - 1998 (522927), страница 43
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Inthe mating Aa × Aa, the probability that any particular pup has the standard coat color is 3/4, and that of aleutian is1/4. Therefore, in a litter of size 8, the probability of 0, 1, 2, 3, . . . pups with the standard coat color is given bysuccessive terms in the binomial expansion of [(3/4) + (1/4)]8. The specific probability of r standard pups and 8 — raleutian pups is given by 8!/[r!(8 — r)!] × (3/4)r × (1/4)(8—r).(a) The probability that none is aleutian means that r = 8, so the probability is(b) A perfect 3 : 1 ratio in the litter means that r = 6, and the probability is(That is, a little less than a third of the litters would have the "expected" Mendelian ratio.)(c) A 1 : 1 distribution in the litter means that r = 4, and the probability isProblem 4: Certain varieties of maize are true-breeding either for colored aleurone (the outer layer of the seed) orfor colorless aleurone.
A cross of a colored variety with a colorless variety gave an F1 with colored seeds. Among1000 seeds produced by the cross F1 × colored, all were colored; and, among 1000 seeds produced by the cross F1 ×colorless, 525 were colored, and 475 were colorless.(a) What genetic hypothesis can explain these data?(b) Using the criterion of a X2 test, evaluate whether the data are in satisfactory agreement with the model.Answer: (a) Mendelian segregation in a heterozygote is suggested by the 525 : 475 ratio, and dominance is impliedbyPage 119(text box continued from previous page)then select w.
Near the bottom of the report, select Full, and then read the section on phenotypic information. Ifassigned to do so, select the allele number 1 (not+1) and write a 100-word report on the molecular basis of the w1mutation. In preparing this report, you will find it helpful to return to the search engine and enter the keywordDoc.4. Using the keyword controversies, you can learn about at least nine controversial issues concerning Mendel'smotivation for doing his work or about aspects of the work itself. If assigned to do so, pick any three of thesecontroversial issues and write a paragraph about each, describing the issue and summarizing the opinions of thoseon opposite sides of the matter.MUTABLE SITE EXERCISESThe Mutable Site Exercise changes frequently. Each new update includes a different exercise that makes use ofgenetics resources available on the World Wide Web. Select the Mutable Site for Chapter 3, and you will belinked to the current exercise that relates to the material presented in this chapter.PIC SITEThe Pic Site showcases some of the most visually appealing genetics sites on the World Wide Web.
To visit theshowcase genetics site, select the Pic Site for Chapter 3.the crosses of colored × colorless and F1 × colored. Therefore, a hypothesis that seems to fit the data is that there is adominant allele for colored aleurone (say, C) and the true-breeding colored and colorless varieties are CC and cc,respectively. The F1 has the genotype Cc. The cross F1 × colored (CC) yields 1 CC : 1 Cc progeny (all colored), andthe cross F1 × colorless (cc) is expected to produce a 1 : 1 ratio of colored (Cc) to colorless (cc). (b) The expectednumbers are 500 colored and 500 colorless, and therefore the X2 equals (525 - 500)2/500 + (475–500)2/500 = 2.5.Because there are two classes of data, there is 1 degree of freedom, and the P value is approximately 0.12 (seeFigure 3.20).
The P value is greater than 0.05, so the goodness of fit is regarded as satisfactory.Analysis and Applications3.1 At what stage in mitosis and meiosis are the chromosomes replicated? When do the chromosomes first becomevisible in the light microscope?3.2 If a cell contains 23 pairs of chromosomes immediately after completion of mitotic telophase, how manychromatids were present in metaphase?3.3 The Greek roots of the terms leptotene, zygotene, pachytene, diplotene, and diakinesis literally mean thin thread,paired thread, thick thread, doubled thread and moving apart, respectively. How are these terms appropriate indescribing the appearance and behavior of the chromosomes during prophase I? (Incidentally, the ending -tenedenotes the adjective; the nouns are formed by dropping -tene and adding -nema, yielding the alternative termsleptonema, zygonema, pachynema, diplonema, and diakinesis, which are preferred by some authors.)3.4 The first meiotic division is often called the reductional division and the second meiotic division the equationaldivision.
Which feature of the chromosome complement is reduced in the first meiotic division and which is keptequal in the second?Page 1203.5 Maize is a diploid organism with 10 pairs of chromosomes. How many chromatids and chromosomes arepresent in the following stages of cell division:(a) Metaphase of mitosis?(b) Metaphase I of meiosis?(c) Metaphase II of meiosis?3.6 Sweet peas have a somatic chromosome number of 14.
If the centromeres of the 7 homologous pairs aredesignated as Aa, Bb, Cc, Dd, Ee, Ff, and Gg.(a) how many different combinations of centromeres can be produced during meiosis?(b) what is the probability that a gamete will contain only centromeres designated by capital letters?3.7 Emmer wheat (Triticum dicoccum) has a somatic chromosome number of 28, and rye (Secale cereale) has asomatic chromosome number of 14. Hybrids produced by crossing these cereal grasses are highly sterile and havemany characteristics intermediate between the parental species. How many chromosomes do the hybrids possess?3.8 X-linked inheritance is occasionally called crisscross inheritance.
In what sense does the X chromosome moveback and forth between the sexes every generation? In what sense is the expression misleading?3.9 The most common form of color blindness in human beings results from an X-linked recessive gene. Aphenotypically normal couple have a normal daughter and a son who is color-blind. What is the probability that thedaughter is heterozygous?3.10 The mutation for Bar-shaped eyes in Drosophila has the following characteristics of inheritance:(a) Bar males X wildtype females produce wildtype sons and Bar daughters,(b) The Bar females from the mating in part a, when mated with wildtype males, yield a 1 : 1 ratio of Bar :wildtype sons and Bar : wildtype daughters.What mode of inheritance do these characteristics suggest?3.11 Vermilion eye color in Drosophila is determined by the recessive allele, v, of an X-linked gene, and thewildtype eye color determined by the v+ allele is brick red.
What genotype and phenotype ratios would be expectedfrom the following crosses:(a) vermilion male × wildtype female(b) vermilion female × wildtype male(c) daughter from mating in part a × wildtype male(d) daughter from mating in part a × vermilion male3.12 The autosomal recessive allele, bw for brown eyes in Drosophila, interacts with the X-linked recessive allele,v, for vermilion, to produce white eyes. What eye-color phenotypes, and in what proportions, would be expectedfrom a cross of a white-eyed female (genotype v v:bw bw) with a brown-eyed male (genotype v+ Y:bw bw)?3.13 It is often advantageous to be able to determine the sex of newborn chickens from their plumage. How couldthis be done by using the W-linked dominant allele S for silver plumage and the recessive allele s for goldplumage? (Remember that, in chickens, the homogametic and heterogametic sexes are the reverse of those inmammals.)3.14 A recessive mutation of an X-linked gene in human beings results in hemophilia, marked by a prolongedincrease in the time needed for blood clotting.
Suppose that phenotypically normal parents produce two normaldaughters and a son affected with hemophilia.(a) What is the probability that both of the daughters are heterozygous carriers?(b) If one of the daughters mates with a normal man and produces a son, what is the probability that the son will beaffected?3.15 In the pedigree illustrated, the shaded symbols represent persons affected with an X-linked recessive form ofmental retardation. What are the genotypes of all the persons in this pedigree?3.16 For an autosomal gene with five alleles, there are fifteen possible genotypes (five homozygotes and tenheterozygotes).
How many genotypes are possible with live alleles of an X-linked gene?3.17 Attached-X chromosomes in Drosophila are formed from two X chromosomes attached to a commoncentromere. Females of genotype C(1)RM Y, in which C(1)RM denotes the attached-X chromosomes, produce C(1)RM-bearing and Y-bearing gametes in equal proportions. What progeny are expected to result from the matingbetween a male carrying the X-linked allele, w, for white eyes and an attached-X female with wildtype eyes? Howdoes this result differ from the typical pattern of X-linked inheritance? (Note: Drosophila zygotes containing threeX chromosomes or no X chromosomes do not survive.)3.18 People who have the sex chromosome constitution XXY are phenotypically male. A woman heterozygous foran X-linked mutation for color blindness mates with a normal man and produces an XXY son, who is color-blind.What kind of nondisjunction can explain this result?Page 1213.19 Mice with a single X chromosome and no Y chromosome (an XO sex-chromosome constitution) are fertilefemales.
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