Answer to Question #155202 in Genetics for Ashwani Kumar Gupta

Question

Task 1. Describe the crossing schemes and indicate the splitting by genotype and phenotype.

Take, for example, that A is brown eyes and a is blue.

1.1 Splitting by phenotype and genotype when crossing homozygotes by dominant and recessive in the case of complete dominance?

1.2 Splitting by phenotype and genotype when crossing heterozygotes in the case of complete dominance?

1.3 Splitting by phenotype and genotype when crossing heterozygote and homozygote by dominant in case of complete dominance?

1.4 Splitting by phenotype and genotype when crossing heterozygote and homozygote by recessive in case of complete dominance?

Answer 1

1.1) For a gene that is expressed in a dominant and recessive pattern, homozygous dominant and heterozygous organisms will look identical (that is, they will have different genotypes but the same phenotype), and the recessive allele will only be observed in homozygous recessive individuals.

1.2) When plants of the F1 generation are self-pollinated, the phenotypic and genotypic ratio of the F2 generation will be 1:2:1 (Red:Spotted:White). These ratios are the same as those for incomplete dominance.

1.3) When a single trait is being studies, a test cross is a cross between an individual with the dominant phenotype but of unknown genotype (homozygous or heterozygous) with a homozygous recessive individual. If the unknown is heterozygous, then approximately 50% of the offspring should display the recessive phenotype.

1.4) The expected genotype ratio when two heterozygotes are crossed is 1 (homozygous dominant) : 2 (heterozygous) : 1 (homozygous recessive). When a phenotypic ratio of 2 : 1 is observed, there is probably a lethal allele.