HEREDITY NOTES
Some important terms
1. Chromosomes are long thread-like structures present in the nucleus of a cell
which contain hereditary information of the cell in the form of genes.
2. DNA is a chemical in the chromosome which carries the traits in a coded
form.
3. Gene is the part of a chromosome which controls a specific biological
function.
4. Contrasting characters: A pair of visible characters such as tall and dwarf,
white and violet flowers, round and wrinkled seeds, green and yellow seeds
etc.
5. Alleles are different forms of the same gene. ... An example of alleles for
flower colour in pea plants are the dominant purple allele, and the recessive
white allele; for height they are the dominant tall allele and recessive
short allele.
6. Homozygous: A condition in which both the genes received from both the
parents are of same type for example; an organism has both the genes for
tallness it is expressed as TT and genes for dwarfness are written as tt.
7. Heterozygous: A condition in which both the genes received from both the
parents are of different types for example; an organism has genes Tt it means
it has a gene for tallness from one parent and the other for dwarfness from
other parent but only tall character is expressed as it is a dominant gene.
8. Dominant trait: The character which expresses itself if it is present in both
homozygous as well as heterozygous condition in a (F1) generation is dominant
trait. Example : Tallness is a dominant character in pea plant.
9.. Recessive trait: The character which does not express itself in the presence
of the dominant trait but is able to express only if present in the homozygous
form is recessive trait. Ex. dwarfism in the pea plant.
10. Genotype: It is genetic make up of an individual, in a gene pair what type of
genes have been received from the parents for example; A pure tall plant is
expressed as TT and hybrid tall as Tt.
11. Phenotype: It is external appearance of the organism for example; a plant
having Tt composition will appear tall although it has gene for dwarfness.
12. Homologous pair of characters are those in which one member is
contributed by the father and the other member by the mother and both have
genes for the same character at the same position.
Mendel’s work
Gregor Johann Mendel, known as ‘Father of Genetics’, was an
Austrian Monk who worked on pea plants to understand the concept
of heredity.
