Concept explainers
In the guinea pig, one locus involved in the control of coat color may be occupied by any of four alleles: C (full color), ck (sepia), cd (cream), or ca (albino), with an order of dominance of: C > ck > cd > ca. (C is dominant to all others, ck is dominant to cd and ca, but not C, etc.) In the following crosses, determine the parental genotypes and predict the
- (a) sepia × cream, where both guinea pigs had an albino parent
- (b) sepia × cream, where the sepia guinea pig had an albino parent and the cream guinea pig had two sepia parents
- (c) sepia × cream, where the sepia guinea pig had two full-color parents and the cream guinea pig had two sepia parents
- (d) sepia × cream, where the sepia guinea pig had a full-color parent and an albino parent and thecream guinea pig had two full-color parents
(a)
To determine: The parental genotype of sepia and cream coated pigs that had an albino parent and the phenotypic ratio of the cross between sepia and cream pigs.
Introduction: In guinea pig, one locus that controls the coat color may have four alleles: C, ck, cd, or ca. ca is the least dominant allele, and C is dominant to all other alleles.
Explanation of Solution
If sepia and cream coated pigs have albino parent, the genotype of sepia and cream pigs will be ckca and cdca, respectively. The cross between ckca and cdca results in
Thus, the genotype of sepia pig is ckca, and cream pig is cdca, and the phenotypic ratio of the cross
(b)
To determine: The parental genotype of sepia and cream coated pigs that had an albino parent and two sepia parents respectively and the phenotypic ratio of their cross.
Introduction: The cream guinea pig could be formed by the cross between ckcd and ckcd or the cross between ckcd and ckca.
Explanation of Solution
If sepia had albino parent, the genotype of sepia guinea pig would be ckca. The genotype of cream guinea pig could be cdcd or cdca.
The cross between sepia guinea pig with genotype ckca and cream guinea pig with genotype cdcd results in
The cross between sepia guinea pig with genotype ckca and cream guinea pig with genotype cdca results in
Thus, the genotype of sepia pig is ckca, and cream pig could be cdcd or cdca. The phenotypic ratio of the cross
(c)
To determine: The parental genotype of sepia and cream coated pigs that had two full-color parents and two sepia parents respectively and the phenotypic ratio of their cross.
Introduction: The genotype of sepia guinea pig parent could be Cck, Ccd, or Cca and not CC because sepia could not be produced.
Explanation of Solution
The genotype of sepia pig could be ckck, ckcd, or ckca. Cream pig could be formed by the cross between ckcd and ckcd or the cross between ckcd and ckca. The genotype of cream guinea pig could be cdcd or cdca.
The cross between sepia guinea pig with genotype ckck and cream guinea pig with genotype cdcd forms all sepia pigs. The cross between sepia guinea pig with genotype ckck and cream guinea pig with genotype cdca also forms all sepia pigs.
The cross between sepia guinea pig with genotype ckcd and cream guinea pig with genotype cdcd forms
The cross between sepia guinea pig with genotype ckca and cream guinea pig with genotype cdca forms
Thus, the genotype of sepia pig could be ckck, ckcd, or ckca, and cream guinea pig could be cdcd or cdca. The crosses
(d)
To determine: The parental genotype of sepia and cream coated pigs that had full-color parent, and albino parent and two full-color parents respectively and the phenotypic ratio of their cross.
Introduction: Sepia guinea pig is formed by the cross between Cck and caca. The cream pig had two full-color parents that could be Ccd or Cca.
Explanation of Solution
The genotype of the sepia pig must be ckca. The cream pig had two full-color parents that could be Ccd or Cca. The genotype of a cream pig could be cdcd or cdca.
The cross between sepia guinea pig with genotype ckca and cream guinea pig with genotype cdcd forms
Thus, the genotype of sepia pig must be ckca, and cream guinea pig could be cdcd or cdca. The phenotypic ratio of cross
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