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Introduction Heredity: tendency of an individual to resemble his parents Variation: the differences between individuals of the same species Genetics:

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Presentation on theme: "Introduction Heredity: tendency of an individual to resemble his parents Variation: the differences between individuals of the same species Genetics:"— Presentation transcript:

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3 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

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

5 white purple x pure-breeding parents first filial (F 1 ) generation second filial (F 2 ) generation all purple 705 purple 224 white monohybrid ratio 3:1

6 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

7 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

8 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

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

10 22 pairs are identical in both sexes (human) –autosomes The 23rd pair is different in male and female –sex chromosomes

11 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

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

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

14 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 Causes of Variations

15 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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