Question

Be able to assign allelic symbols for crosses with novel traits to be able to analyze related crosses.

A. Since the phenotypes of alleles for the different characters we will deal with in this chapter have a clear dominant/recessive relationship, it may be ideal to label the recessive allele with lower case and the dominant allele with either an upper case or if dominant allele is the wild-type allele one could label it with a lowercase followed by a + sign as in Drosophila genetics.

B. If a pair of alleles are being discussed such as a wild type allele whose phenotype is recessive to the phenotype of another dominant allele (e.g. a dominant disease causing allele), the dominant allele may be written in uppercase.Take home message: when a pair of alleles with a clear dominant/recessive relationship are being discussed, NEVER label the recessive allele in uppercase.

C. This simple strategy will allow you to accurately predict phenotypes from diploid genotypes.

Answer 1

The use of uppercase and lowercase letters in genetic nomenclature helps differentiate dominant from recessive alleles, with uppercase representing dominant traits and lowercase for recessives.

Step-by-step explanation:

In genetics, it is standard to use capital and lowercase letters to distinguish between dominant and recessive alleles. For instance, in Mendel's classic pea plant experiments, the tall trait (T) is dominant, and the dwarf trait (t) is recessive. Thus a homozygous tall pea plant is represented as TT, a homozygous dwarf as tt, and a heterozygous tall plant as Tt.

Dominance means that the phenotype of the dominant allele will be expressed in both homozygous dominant (AA) and heterozygous (Aa) organisms. Fundamental to predicting phenotypes from genotypes is the understanding that a homozygous recessive organism (aa) will express the recessive trait because there is no dominant allele to mask its effect.