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#dominant parent

2 public questions tagged with this topic.

Genetic Crosses

A phenotypic ratio of 1:1 in progeny from a dominant × recessive cross indicates the dominant parent is

A cross between phenotypically dominant individual of unknown genotype and homozygous recessive tester aa produces progeny ratio reflecting gametes from dominant parent. If dominant parent were AA, only A gametes form, so all offspring Aa show dominant phenotype. If dominant parent were heterozygous Aa, meiosis yields equal A and a gametes, producing Aa dominant and aa recessive progeny in 1:1 proportion. Observing 1:1 dominant to recessive therefore diagnoses heterozygosity. This logic excludes homozygous dominant, homozygous recessive, and hemizygous interpretations for autosomal monohybrid trait with complete dominance.

Ref: Klug et al., Concepts of Genetics, 12th ed., Chapter 3: Interpreting 1:1 Test Cross Ratio

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Mendelian Inheritance

In a monohybrid back cross with dominant parent, progeny will be

Monohybrid back cross with dominant parent TT mated to F1 Tt allows dominant parent to contribute only T gametes, F1 generates T and t gametes equally. Fertilisation yields genotypes TT and Tt in 1:1 proportion, both bearing at least one dominant allele T. Because T shows complete dominance over t, all progeny display dominant phenotype such as tall, no recessive phenotype expressed. Recessive appearance requires tt genotype impossible with TT parent, 3:1 appears in selfing, 1:1 ratio occurs only when back crossed to recessive tester.

Ref: Hartl & Ruvolo, Genetics, 9th ed., Chapter 2: Back Cross with Dominant Parent

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