Differentiate between the following -
(a) Dominance and Recessive
(b) Homozygous and Heterozygous
(c) Monohybrid and Dihybrid.
Differentiate between the following -
(a) Dominance and Recessive
(b) Homozygous and Heterozygous
(c) Monohybrid and Dihybrid.
Solution and Explanation
(a) Dominance and Recessive
| - | Dominance | Recessive |
| 1. | A dominant factor or allele expresses itself in the presence or absence of a recessive trait. | A recessive trait is able to express itself only in the absence of a dominant trait. |
| 2. | For example: tall plant round seed violet flowers etc. are dominant characters in a pea plant. | For example: dwarf plant wrinkled seed white flower etc. are recessive traits in a pea plant. |
(b) Homozygous and Heterozygous
| - | Homozygous | Heterozygous |
| 1. | It contains two similar alleles for a particular trait | It contains two different alleles for a particular trait. |
| 2. | Genotype for homozygous possess either dominant or recessive but never both alleles. For example RR or rr | Genotypes for heterozygous possess both dominant and recessive alleles. For example Rr |
| 3. | It produces only one type of gamete. | It produces two different kinds of gametes. |
(c) Monohybrid and Dihybrid
| - | Monohybrid | Dihybrid |
| 1. | Monohybrid involves a cross between parents which differs in only one pair of contrasting characters. | IDihybrid involves a cross between parents which differs in two pairs of contrasting characters. |
| 2. | For example, the cross between tall and dwarf pea plant is a monohybrid cross. | For example, the cross between pea plants having yellow wrinkled seeds with those having green round seeds is a dihybrid cross. |
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Notes on Principles of Inheritance and Variation
Concepts Used:
Principles of Inheritance and Variation - Mutation
A Mutation is a change in the sequence of our DNA base pairs caused by numerous environmental stimuli such as UV light or mistakes during DNA replication. Germline mutations take place in the eggs and sperm and can be passed onto offspring, whereas somatic mutations take place in body cells and are not passed on.
Types of Mutations
There are three types of mutations, which are as follows:
Silent mutation
It refers to any change in DNA sequence that has no effect on the amino acid sequence in a protein or the functions that a protein performs. There is no phenotypic indication that a mutation has occurred.
Nonsense mutation
When there is a change in the sequence of base pairs due to a point mutation, that results in a stop codon. This leads to a protein that is either shortened or non-functional.
Missense mutation
A missense mutation occurs when a point mutation causes a change in the codon, which then codes for another amino acid.
The mutation is caused by the following factors:
Internal Causes
When DNA copies incorrectly, the majority of mutations occur. Evolution occurs as a result of all of these mutations. DNA makes a copy of itself during cell division. When a copy of DNA isn't flawless, it's called a mutation since it differs somewhat from the original DNA.
External Causes
When certain chemicals or radiations are used to break down DNA, it causes the DNA to break down. The thymine dimers are broken by UV radiation, resulting in altered DNA.