Question

What is the law of dominance of traits? Explain with an example.

Answer 1

Law of dominance:

1. The Law of dominance was given by Gregor Mendel, who discovered the basic principles of heredity.
2. It states that “When parents with pure, contrasting traits are crossed together, only one form of trait appears in the next generation".
3. Generally, there are two alleles responsible for a particular trait appearing in an organism, among those, the dominant allele will exhibit its effect more strongly than the recessive one.
4. In other words, the dominant allele suppresses the recessive allele in heterozygous conditions.
5. Heterozygous refers to a situation in which one dominant allele and one recessive allele responsible for the same trait occur together.
6. Homozygous refers to a condition in which either a dominant allele or recessive allele occur together.

For example:

1. Consider the height of the plant, ‘T’ denotes tallness and ‘t’ denotes the dwarf nature of the plant.
2. The allele “T” is dominant over the allele “t” in the pea plant.
3. Consider an example of a plant with genotype Tt crossed with Tt and is appearing “tall” phenotypically.
4. A Punnett square representation of the cross is illustrated below.

	T	t
T	TT (tall)	Tt (tall)
t	Tt (tall)	tt (dwarf)

1. The genotypic ratio of the above cross is 1:2:1, one plant has two dominant alleles and appears tall, two plants have one dominant and one recessive allele, and one plant has two recessive alleles and appears dwarf.
2. The phenotypic ratio is 3:1 that is three plants are appeared to be tall and one is a dwarf.