Multiple alleles:

 ð  More than two genes occupying the same locus on some pair of homologous chromosomes.

 ð  E.g.:- Inheritance of blood groups in human beings has 4 groups i.e. A, AB, O and  B which are formed with the presence of 3 genes.

Incomplete dominance:

 ð  Expression of dominant gene is incomplete or partial.

 ð  E.g.:- Color of a flower.

Test cross:

 ð  Cross between the F1 hybrid and recessive plant is known as test cross.

 ð  Significance of test cross:-

a)      It is conducted to make sure of the genotype of F1.

b)      Determines if dominant character is because of a homozygous or heterozygous condition.

c)       50%  show dominance and 50% show recessive.

d)      Both monohybrid and di hybrid test cross are conducted.

Back cross:

 ð  Cross between the F1 hybrid with one of its parents or with an individual genetically identical to the parent

Mendelian concepts of heredity:

   a)      Concept of Unit character:

 ð  Factors responsible for expression of characters are called unit characters or alleles.

   b)      Concept of purity of gametes:

 ð  It suggests a gamete carries only one gene which regards to one character

   c)       Concept of dominance:

 ð  The traits which appear in F1 generation are dominant and the traits which don’t appear in F1 generation are recessive, when two pure bred plants are cross pollinated.

   d)      Law of segregation:

 ð  In a cross involving a single character, the factors responsible for the two contrasting traits stay together in F1 generation but segregate during the formation of gametes.

   e)      Law of independent assortment:

 ð  In a di hybrid cross where two contrasting characters are brought together, factors responsible for 2 pairs of contrasting characters stay in F1 generation but assort independently in during the formation of gametes.

The 7 characteristics of pea plants:

 ð  Purple and white flower

 ð  Axillary and terminal flower

 ð  Yellow and green seeds

 ð  Round and wrinkled seeds

 ð  Green pod and yellow pod

 ð  Inflated pod and constricted pos

 ð  Tall and dwarf plant

Recessive:

      Alleles which have same phenotypic effect only in homozygous conditions.