Concept explainers
In 1919, Calvin Bridges began studying an X-linked recessive mutation causing eosin-colored eyes in Drosophila. Within an otherwise true-breeding culture of eosin-eyed flies, he noticed rare variants that had much lighter cream-colored eyes. By intercrossing these variants, he was able to make a true-breeding cream-eyed stock. Bridges now crossed males from this cream-eyed stock with true-breeding wild-type females. All the F progeny had red (wild-type) eyes. When F flies were intercrossed, the F progeny were 104 females with red eyes, 52 males with red eyes, 44 males with eosin eyes, and 14 males with cream eyes. Assume that these numbers represent an 8:4:3:1 ratio.
Formulate a hypothesis to a. explain the F1 and F2 results, assigning
phenotypes to all possible genotypes?What do you predict in the F1 and F2 generations if the parental cross is between true-breeding eosin eyed males
and true-breeding cream eyed females?What do you predict in the F1 and F2 generations if the parental cross is between true-breeding eosin eyed females
and true-breeding cream eyed males?
a.
To determine:
The hypothesis derived from the results obtained from crossing true breeding cream-colored male and true-breeding wild female.
Introduction:
Fertilization is the process by which the male gamete, sperm, fertilize with the female gamete, ovary. The process brings about the fusion of two haploid pronuclei into a diploid zygote.
Explanation of Solution
The hypothesis that can be derived from the results is that mutation in the wild type allele results in the production of eosin eyed progeny. The presence of criss-cross inheritance in the wild and the mutated variant results in the production of cream eyed progeny. This hypothesis supports the presence of criss-cross inheritance.
b.
To determine:
The predicted progeny in F1 and F2 generation if the cross is made between true-breeding eosin eyed males and true-breeding cream-colored females.
Introduction:
The dominant allele masks the expression of the recessive allele. Therefore, the dominant allele is expressed in homozygous and heterozygous genotype while the recessive phenotype is only expressed under homozygous condition.
Explanation of Solution
The progeny from the cross between true-breeding eosin eyed males, and true-breeding cream-colored females are as follows:
Gametes | Xe | Y |
Xc | Xe Xc |
Xc Y |
Xc | Xe Xc |
Xc Y |
The F2 progeny is derived as follows:
Gametes | Xc | Y |
Xe | Xe Xc |
Xe Y |
Xc | Xc Xc |
Xc Y |
The progeny obtained will be cream eyed males (Xc Y), eosin eyed males (Xe Y), cream-colored females (Xc Xc) and variant cream colored female (Xe Xc).
b.
To determine:
The predicted progeny in F1 and F2 generation if the cross is made between true-breeding eosin eyed females and true-breeding cream colored males.
Introduction:
The Punnett square is used to depict the genetic cross between two parents and all the possibilities of the resulting progeny that can help in identifying the genotype and phenotype of the hybrids produced.
Explanation of Solution
The progeny from the cross between true-breeding eosin eyed females, and true-breeding cream colored males are as follows:
Gametes | Xc | Y |
Xe | Xc Xe |
Xe Y |
Xe | Xc Xe |
Xe Y |
The F2 progeny will be derived as follows:
Gametes | Xe | Y |
Xe | Xe Xe |
Xe Y |
Xc | Xe Xc |
Xc Y |
The progeny obtained will have male genotype Xc Y, and Xe Y and females will have genotype Xe Xe and Xe Xc
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Chapter 4 Solutions
Genetics: From Genes to Genomes
- In Drosophila, a cross was made between females—all expressing the three X-linked recessive traits scute bristles (sc), sable body (s), and vermilion eyes (v)—and wild-type males. In the F1, all females were wild type, while all males expressed all three mutant traits. The cross was carried to the F2 generation, and 1000 offspring were counted, with the results shown in the following table. Phenotype Offspring sc s v 314 + + + 280 + s v 150 sc + + 156 sc + v 46 + s + 30 sc s + 10 + + v 14 No determination of sex was made in the data. (a) Using proper nomenclature, determine the genotypes of the P1 and F1 parents. (b) Determine the sequence of the three genes and the map distances between them. (c) Are there more or fewer double crossovers than expected? (d) Calculate the coefficient of coincidence. Does it represent positive or negative interference?arrow_forwardIn the fruit fly, dumpy wings (d) and purple eyes (p) are encoded by mutant alleles that are recessive to those that produce wild type traits; long wings (d+) and red eyes (p+). These two genes are on the same chromosome. In a particular lab, two researchers Walt and Jesse crossed a fly homozygous for dumpy wings and purple eyes with a fly homozygous for the wild type traits. The F1 progeny, which had long wings and red eyes, was then crossed with flies that had dumpy wings and purple eyes. Unfortunately, the progeny of this cross somehow escaped. To prevent their other projects from contamination, they decided to spend an exceptionally boring hour in the lab catching and counting the progeny and found the following: long wings, red eyes – 482 dumpy wings, purple eyes – 473 long wings, purple eyes – 23 dumpy wings, red eyes - 22 What is the genetic distance between these two loci? a. 4.5 cM b. 55 cM c. 45 cM d. 49.5 cM e. 4.7 cMarrow_forwardMale Drosophila from a true-breeding wild-type stock were irradiated with X-rays and then mated with females from a true-breeding stock carrying the following recessive mutations on the X chromosome: yellow body (y), crossveinless wings (cv), cut wings (ct), singed bristles (sn), and miniature wings (m). These markers are known to map in the order: Recessive alleles: y, cv, ct, sn, m Dominant alleles: y+, cv+, ct+, sn+, m+ y-cv-ct-sn-m у CV ct sn m X-rays х х X ct sn CV у m y+ CV+ ct+ sn+ m+ х X ? Exceptional female: Most of the female progeny of this cross were phenotypically wild type, but one female exhibited ct and sn mutant characteristics. When this exceptional ct sn female was mated with a male from the true-breeding wild-type stock, twice as many females as males appeared among the progeny. a. What is the nature of the X-ray-induced mutation present in the exceptional female? b. Draw the X chromosomes present in the exceptional ct sn female as they would appear during pairing…arrow_forward
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