heredity and variation for 10th 11111.pptx

Heredity and variation

1. Transmission of characters from one generation to the next generation is called heredity Variations are existed in the wild populations of plants &animals

2. Heredity :- The transfer of characters or traits from the parents to their off springs is called heredity. Variations :- The differences between the characters or traits among the individuals of the same species are called variations.

3. Accumulation of variations during reproduction When organisms reproduce, the off springs show minor variations due to inaccuracies in DNA copying. These variations are less in asexual reproduction and more in sexual reproduction . Some variations are useful variations and they help the organism to adjust to the changes in the environment. Some variations do not help the organism to adjust to the changes in the environment and they may die and become extinct.

4. Rules for inheritance of characters (traits) :- Characters are transferred through genes present in the DNA molecules in the chromosomes present in the nucleus of the cell . The inheritance of characters is due to the fact that both the father and mother contributes equal amount of genetic material to the child. So for each trait there are two factors one from the father and one from the mother. Gregor Johann Mendel conducted experiments with garden pea plants and determined the rules for the inheritance of traits.

5. Mendel work on inheritance T r a it D o m i nant character R e c e ssi v e character

6. Inheritance of single gene

7. • Self pollination is the second step in Mendel experiment The F 1 plants are self pollinated The dominant & recessive characters are expressed in 3;1 ratio The trait that is expressed i n t h e F 1 ge ner a ti o n is ca ll e d the dominant trait and the trait that is supressed in the F 1 is called the recessive trait.

8. INHERITANCE OF SINGLE GENE FI generation F2 generation

9. Mendel conclusions based on his observations 1. Mendel proposed that some thing was being stably passed down, unchanged from parents to offsprings through the gametes , over successive generations . He called these things as the factors. Now we call them as genes

10. AL L E L ES

11. Genes & Alleles Genes are the units of the inheritance They contain the information that is required to express a particular trait in an organism Genes which code for a pair of contrasting characters are known as alleles Different forms of the same gene are said to be alleles

12. Homozygous & Heterozygius condition If the two alleles of the gene are similar , it is said to be homozygous condition If the two alleles of the gene are dissimilar , it is said to be heterozygous condition TT, tt Homozygous condition Tt Heterozygous condition T denotes the dominant trait t denotes the recessive trait TT, Tt denote the character tall tt denote the character dwarf

13. Genes, Alleles, and YY Yy y y Y Y Y y y y

14. PHENOTYPE & GENOTYPE Observable character of the trait is called Phenotype . It is a descriptive term Ex- Tall or Dwarf Genetic constitution of the trait is said to be Genotype Ex- TT, Tt, tt

15. When plants having two pairs of characters (Eg:- shape and colour of seeds) were crossed (Dihybrid cross) :- Mendel selected pea plants having two pairs of characters – shape and colour of seed. He selected plants having round yellow seeds (RRYY) and wrinkled green seeds (rryy) and cross pollinated them. He obtained all plants with round yellow seeds (RrYy) in the F 1 generation. When these plants were self pollinated in the F 2 generation out of 16 plants, 9 had round yellow (RrYy), 3 had round green (Rryy), 3 had wrinkled yellow (rrYy) and 1 had wrinkled green (rryy) seed. In the ratio 9:3:3:1.

16. Mendal laws 1. Law of dominance 2, Law of segregation 3. Law of independent assortment The first two laws are derived from the monohybrid cross The third law is derived from the dihybrid cross

17. Law of dominance Dominant character is expressed in F1 generation. Dominant & recessive characters are expressed in 3;1 ratio in F2 generation

18. Law of segregation The two alleles of the trait segregate from each others so that gamete receives only one of two factors

19. Law of independent assortment The alleles of one trait segregate into the gametes independent of alleles of other traits Y y R Rr r Y y

20. Sex determination in human beings :- Human beings have 23 pairs of chromosomes in the nucleus of the cell. Out of this two chromosomes are sex chromosomes X and Y. The female has two X chromosomes (XX) and male has one X and one Y chromosome (XY). The sperms and eggs have one set of sex chromosomes. Some sperms have X chromosome and some have Y chromosome. All eggs have X chromosome. If a sperm having X chromosome fuses with an egg having X chromosome the child will be a girl. If a sperm having Y chromosome fuses with an egg having X chromosome the child will be a boy.