Question

How many phenotypes will be obtained from a test cross Aa Bb Cc?

Answer 1

Phenotypes:

• The term "phenotype" refers to the observable physical properties of an organism.
• Phenotypes is the term used to define the characteristics or traits used in study of genetics of an organism.
• Phenotype describes the development process, morphology or physical form, behavior, biochemical and physiological characters of an organism.
• Anything that is dependent on genotype is known as phenotype including proteins and RNA molecules.

Number of phenotypes:

• A test cross is an experimental cross of an individual organism of dominant phenotype but unknown genotype and an organism with a homozygous recessive genotype (and phenotype).
• The formula to know the number of possible phenotypes from two parents in a test cross is $2^n$ in which n describes the number of pairs of characters or the number of pair of heterozygous pair of alleles in the genotype of the parent.
• Therefore, the genotype of one parent is aabbcc and will produce only one kind of gamete abc and the genotype of another parent is AaBbCc and will produce 8 types of gametes, i.e., ABC, AbC, ABc, Abc, abc, aBc, abC, and aBC.
• In this way 8 types of phenotypes will be obtained from this cross- AaBbCc, AabbCc, AaBbcc, Aabbcc, aabbcc, aaBbcc, aabbCc and aaBbCc.
• Also, since in the heterozygous parent 3 genes are in heterozygous condition, i.e., n = 3, therefore according to the formula, $2^n=2^3=8$.
• Hence, 8 phenotypes are possible.