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. 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

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) 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

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
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

15. ~ END ~