Heredity and Evolution
- New indivisuals are produced by reproductive process, which are similar to parents but something differ.
- We get more diversities by sexual reproduction.
- Selection of variants by environmental factors forms the basis for evolutionary processes.
Genetics: Genetics is the study of heredity and variation.
Heredity: Transmission of characters/traits from one generation to the next generation is called heredity.
Variations: The differences in the characters/traits between the parents and offspring are called variations.
Inherited Traits : Those special traits with basic traits which inherited from their parents are callled inherited traits.
Example: Free and attached earlobes in human, colours of skin, colours eyes etc.
Types of variations: There are two types of variations.
(i) Somatic Variation:
(ii) Gametic Variation:
Differences between Somatic Variation and Gamatic Variation
(i) This variation comes in body cells.
(ii) They do not inherit in the next generations.
(iii) They are not helpful in evolution.
(iv) These are also called aquared traits.
(v) Example, boring of pinna, cutting of tails in dogs.
(ii) This variation comes in reproductive cells.
(ii) They inherit in the next generations.
(iii) They are helpful in evolution.
(iv) They are also called genetic traits.
(v) Example, human height, skin colour.
Accumulation of variation during reproduction :
Variations accumulate during reproduction in the offspring. In asexual reproduction new indivisuals are quite similar and there are less variations. Because;
(i) There generated very less errors (inaccuracy) during DNA copying.
(ii) Involving of single parent.
While if sexual reproduction is involved, even greater diversity will be generated. The reasons are as follow;
(i) large variations appear due to large errors.
(ii) Diversity comes due to cross breeding and involving of male and female gamate.
(iii) Separation of chromosomes.
Mendel's Experiment And Rule for Inheritance of Traits:
Mendel's porposed some majors rule for inheritance. He is the father of genetics. Mendel used a number of contrasting characters for garden pea. He selected peas (Pisum Sativum) plants for his experiment. This is why that :
(i) Peas plants are annual plants
(ii) These complete their life cycle in one season and give fruits and flowers.
(iii) There are variety of species of peas plants and all traits are macroscopically visible.
(iv) Normally allows self-fertilisation but cross-fertilisation can also be
Examples: round and wrinkle seed, tall and short, while flower and purple and yellow seed and green seed plants.
Mendel used seven alternative (contrasting) characters of pea plants for his experiment which as follow:
Rules for inheritance of traits:
(i) The rule for inheritance in human being is based on this that the parents transfer equal amount of genetic materials in the offspring.
(ii) There are two options for each traits in the each offspring.
(iii) Each trait is impressed by the DNA of parents.
Mendel's Experiments and Hybrid Method:
There are two kinds of hybrid mehtod :
(i) Monohybrid Cross:
(ii) Dihybrid Cross:
1. Monohybrid Cross : When the Cross between two pea plants with one pair of contrasting characters is called a monohybrid cross.
Example : Plants of round and wrinkle seed, plants of tall and twarf etc.
2. Dihybrid Cross : When the cross is taken place by taking double traits of two plants is called dihybrid cross.
Example Round and green plants with wrinkled and yellow plants.