22. Two black guinea pigs were mated and over several years produced 29 black an
ID: 58456 • Letter: 2
Question
22. Two black guinea pigs were mated and over several years produced 29 black and 9 white offspring. Explain these results, giving the genotypes of parents and progeny.
b. How would you test your hypothesis.
b. Give genotypes for as many individuals in the pedigree as possible.
43. A man lacks earlobes, whereas his wife does have earlobes. Their first child, a boy, lacks earlobes.
a. If the phenotypic difference is assumed to be due to two alleles of a single gene, is it possible that the gene is X-linked?
b. Is it possible to decide if the lack of earlobes is dominant or recessive?
Explanation / Answer
Answer 22: Two black guinea pigs were mated and over several years produced 29 black and 9 white offspring. Therefore, the ratio of black: white= 3.2:1=3:1.
Based on the ratios obtained, we can clearly understand that black phenotype is dominant over white phenotype.
Genotype of Black- BB, Bb; Genotype of white- bb.
The genotype of black guinea pigs under the experimental conditions of this question is Bb.
Father guinea pig genotype- Bb
Mother guinea pig genotype- Bb
Therefore, genotypes of offsprings obtained are BB, Bb, Bb and bb.
As mentioned above, offsprings with genotypes BB and Bb will be black and offsprings with bb genotype will be white. This explains the 3: 1 ratio of black: white from two black guinea pigs.
Answer 37:
a) The pedigree analysis of the disease in question shows that disease is autosomal recessive disorder. In autosomal recessive disorder, both the alleles of the gene should be mutated such that genotype of a person suffering from autosomal recessive disorder will be aa while the carrier of disease will have Aa genotype. As can be understood from the pedigree, the disease is transferred from father to both son and daughter, hence it is neither X linked nor Y linked. Therefore, the disorder in question is autosomal disorder.
b) Genotypes of the males and females in the pedigree are as follows:
I generation: 1- Aa; 2-aa
II generation: 1- aa; 2-Aa; 3- aa; 4-Aa
III generation: 1-Aa; 2-aa; 3-Aa; 4-aa; 5-AA; 6-Aa; 7-aa; 8- Aa
IV generation -1-aa; 2-Aa; 3- aa; 4-Aa; 5-Aa; 6-Aa; 7-Aa; 8 –aa; 9-aa
Answer 43:
a) Wife has ear lobes, husband is not having ear lobes. But the son born to them lack ear lobes so it is possible that alleles linked to presence/ absence of ear lobes is present of X chromosomes.
b) Based on the given information, it is possible that absence of ear lobes is a recessive character.
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