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

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

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

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

Terms Dominant gene (or character) Recessive 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

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

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

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

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

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

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

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

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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