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Genetics 10th ncert
- 2. Chapter :4 GENETICS part 1 Mohd Riaz Teacher Govt Boys H/S Purani Poonch
- 3. Genetics introduction Variations Sex determination in human beings Mendels work on pea Monohybrid cross Monohybrid cross( conclusions) Terminology
- 4. GENETICS : Genetics is the study of principles and mechanisms of heredity and variations. HEREDITY: Heredity is the inheritance of parental characters. VARIATIONS : In sexually reproducing organisms offsprings exhibit differences in the characters (except identical twins). These differences are termed as variations.
- 6. Variations are the characteristics of sexually reproducing organisms. Many of the variations are useful and develop new characters that help an organism to adjust in varied environmental conditions. In this way variations promote the chances of survival of a species.
- 7. Sex of a child in human beings is determined at the time of fertilization Sex of a child depends upon its genotype. Humans have 44 autosomes and 2 sex chromosomes. Ova produced by female carry only X Chromosome while male produces two types of sperms ,one with Y chromosome and the other with X chromosome. During fertilization if a sperm carrying Y chromosome fuses with ovum it produces a male XY and if a sperm carrying X chromosome fuses with ovum ,it produces a female child.
- 12. GREGOR JOHANN MENDEL WORK ON PEA. Gregor Johann Mendel (1822-1884) was an Austrian monk. He started hybridizing experiments on garden pea (Pisum sativum) from 1857. REASONS OF MENDELS SUCCESS Mendel succeded in establishing his laws whereas the contemporary botanists failed.
- 13. The garden pea can be selfed or crossed with equal ease . He crossed two plants having a pair of contrastion characters. He also kept a complete record of all characters he choose through all the generations he bred(Used Statistical approach) While analysing the data, he took into consideration just one or two characters at a time ,thus avoiding confusion due to intermixing of characters.
- 14. MONOHYBRID CROSS. A cross between two plants having contrasting traits for a single character is called Monohybrid cross . Mendel crossed a tall variety of pea plant with dwarf variety. In this cross only one character i.e height of the plant was taken into consideration.
- 15. TALL
- 17. Mendel crossed a tall plant with a dwarf one and obtained all tall plants in F1 generation. On selfing F1 plants , the F2 offsprings appeared in the ratio of 3 Tall: 1 Dwarf. The reappearance of recessive character in the F2 generation suggests that somewhere in the life history of the plants , the factors controlling the characters segregate.Hence Mendel named his first law as Law of segregation.
- 18. TALL
- 19. LAW OF PAIRED FACTORS. Mendel found that in an organism a character is represented in an organism by two factors.The two factors lie on the two homologous chromosomes. DOMINANCE. Mendel called the character that expressed in F1 generation as dominant and the one which is suppressed as recessive. In Pea tallness is dominant character.
- 20. FACTOR/GENE: It is a hereditary unit that controls one character.Mendel called it Factor. Johannsen coined the term gene in 1909 to describe gene as a physical and functional unit of heredity. ALLELES : Alleles or Allelomorphs are the alternating forms of the same gene. PHENOTYPE: The external menifestation of an individual is known as Phenotype. GENOTYPE : It is the genetic constitution of an individual.e.g TT for pure tall , Tt for hybrid tall. HOMOZYGOUS: An individual having identical alleles for a character. HETEROZYGOUS: An individual having two contrasting alleles for a character. Tt or Yy
- 21. 1. How to sex of a child is determined in human beings. 2. What is monohybrid cross ? Explain the Law of Segregation?