Question

1. In dogs, wire hair (S) is dominant to smooth hair (s). In a cross of a heterozygous wire-haired dog with a smooth haired dog, what will be the phenotypic and genotypic ratios of the F1 generation? Use the Punnett square provided to show your results.

Answer 1

Answer:

The genotypic ratio of the F1 generation is:

1:1 OR 50% heterozygous wire-haired, 50% homozygous smooth-haired.

The phenotypic ratio of the F1 generation is:

1:1 OR 50% wire-haired, 50% smooth haired.

Explanation:

A cross between the parents with genotype:

Parent 1; Ss and Parent 2; ss, will yield two types of progeny. Half the offspring in the F1 generation will be heterozygous wire-haired just as in parent 1, while the other half will be homozygous short-haired as in parent 2.

Demonstrating it with a punnet square:

             S                     s

s            Ss                  ss

s           Ss                   ss                                  2/4 offspring: Ss,

                                                                        2/4 offspring: ss

Since the allele for wire hair is dominant over that of short hair, the presence of one dominant allele, translates into the offspring having wire hair phenotypically or by physical assessment. The offspring who are homozygous for the recessive allele however, express short hair because they carry both alleles for short hair.

Answer 2

The genotypic and phenotypic ratios of the F1 generation in a cross between heterozygous wire-haired dog with a smooth haired dog are 1 Ss: 1Ss and 1 wire haired: 1 smooth haired respectively.

• According to this question, a gene coding for hair texture in dogs. Wire hair (S) is dominant to smooth hair (s).

• If a heterozygous wire-haired dog (Ss) with a smooth haired dog (ss), the following gametes will be produced by each parent:

1. Ss- S and s
2. ss - s and s.

• Using these gametes in a punnet square (see attached image), the following genotypic and phenotypic proportion of offsprings will be produced:

1. Ss - wire haired
2. Ss - wire haired
3. ss - smooth haired
4. ss - smooth haired

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