Genetics and Heredity: Key Concepts and Experiments

2. Introduction Heredity: tendency of an individual to resemble his parents Variation: the differences between individuals of the same species Genetics: the study of how characters are transferred or inherited from one generation to the next

3. Mendel’s Breeding Experiment Monohybrid Inheritance: The inheritance of just one pair of contrasting characters Cross 2 pure breeding parents with contrasting characters

4. x purple white pure-breeding parents first filial (F1) generation all purple second filial (F2) generation 705 purple 224 white monohybrid ratio 3:1

5. Terms • Genotype - the genetic composition • Phenotype - the external appearance • Homozygous (pure-breeding) • with the same alleles in the same character • Heterozygous (hybrid) • with different alleles

6. Terms • Dominant gene (or character) • which expresses its effect even in heterozygous condition • Recessive gene (or character) • which expresses its effect only in homozygous condition • Pedigree • it shows the inheritance of one or more characters in different generations

7. Terms • Test cross • cross the organism with dominant character to an organism with homozygous recessive character • to test whether the organism with the dominant character is homozygous or heterozygous • Back cross • cross an organism with one of its parent

8. Sex Determination • in human : by sex chromosomes • male : XY • female : XX XY XX • chromosomes other than sex chromosomes  somatic chromosomes which control normal body characters

9. 22 pairs are identical in both sexes (human) • autosomes • The 23rd pair is different in male and female • sex chromosomes

10. Twins • identical twins • one embryo separates into two and each develops into a new individual • they should have same characters and same sex • non-identical twins • formed from two different zygotes from two separate fertilizations • they usually have different characters • they may have different sexes

11. Types of Variations • continuous variation • with a continuous range of intermediate values • eg. height, weight, intelligence quotient, heart beat No. of individuals continuous variation human height

12. Types of Variations • discontinuous variation • the character is clear-cut & not showing intermediates • eg. tongue rolling, ear lobes and colour of corn albinism

13. Causes of Variations • Meiosis • homologous chromosomes separate independently from each other and pass into a different gamete ( INDEPENDENT ASSORTMENT). As a result, a great variety of gametes are produced • Random Fertilization • since fertilization is a random process, there are many possible different combinations of genes in a zygote

14. Causes of Variations • Mutation • genetic make-up may suddenly change • sometimes occur naturally • rate may greatly increased if the organism is exposed to radiation, certain chemicals or neutron bombardment • most mutation are harmful • Environmental Factors • cause variation in characters with continuous variation

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