12th Botany notes
CHAPTER-2
CLASSICAL GENETICS
1. Write the importance of variations
(1) Variations make some individuals better fitted in the struggle for existence.
(2) It provides the genetic material for natural selection
2. Explain – types of variation
(1) Discontinuous Variation
Within a population there are some characteristics which show a limited form of variation. Example: Style length in Primula, plant height of garden pea.
(2) Continuous Variation
This variation may be due to the combining effects of environmental and genetic factors. Example: Human height and skin color.
3. Define – heredity and variation
(1) Heredity is the transmission of characters from parents to offsprings.
(2) The organisms belonging to the same natural population or species that shows a difference in the characteristics is called variation.
4. Define the following terms
(1) Alleles
Traits are expressed in different ways due to the fact that a gene can exist in alternate forms for the same trait is called alleles.
(2) Hybrid
Mendels non-true breeding plants are heterozygous, called as hybrids.
5. Define – law of independent assortment
(1) When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent to the other pair of characters.
(2) Genes that are located in different chromosomes assort independently during meiosis.
6. List out the intragenic interactions
(1) Incomplete dominance
(2) Codominance
(3) Multiple alleles
(4) Pleiotropic genes
7. What is incomplete dominance?
When one allele is not completely dominant to another allele it shows incomplete dominance. Such allelic interaction is known as incomplete dominance.
8. What is meant by codominance?
Two alleles are both expressed in the heterozygous individual is known as codominance.
Example: Red and white flowers of Camellia
9. What is “Lethal allele”?
An allele which has the potential to cause the death of an organism is called a “Lethal Allele”
10. What are pleiotropic genes?
(1) In Pleiotropy, the single gene affects multiple traits and alter the phenotype of the organism.
(2) The Pleiotropic gene influences a number ofThe Pleiotropic gene influences a number of characters simultaneously and such genes are called pleiotropic gene.
11. Define – epistatic and hypostatic
The gene that suppresses or masks the phenotypic expression of a gene at another locus is known as epistatic. The gene whose expression is interfered by non-allelic genes and prevents from exhibiting its character is known as hypostatic.
12. What is locus?
The site or position of a particular gene on a chromosome.
13. Define – dominant epistasis
It is a gene interaction in which two alleles of a gene at one locus interfere and suppress or mask the phenotypic expression of a different pair of alleles of another gene at another locus.
3 MARKS
1. Explain – dihybrid test cross
2. Draw dominant epistasis in summer squash
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