Genetics

Genetics - branch of biology that deals and explores how genes are inherited and expressed in an organism. Study of biological information, genes, heredity and variation.

Organism > Cell > Nucleus > Chromatin/chromosome > Genes > DNA

Heredity - transmission of traits from one generation to another

Gene - the unit of heredity occupying a particular location on the chromosome

passed on to the offspring

Variation - difference existing between individuals of the same species due to different set of genes

History of Genetics

Before Mendel

The belief was blending theory of inheritance. Both sexes contribute equally to new individuals. Two set of traits would be combined to make a new trait for the offspring. Ex. Black sheep and white sheep would have an offspring of gray sheep.

However, due to mendel’s discovery it was proved against this theory that traits are inherited independently and not necessarily blended.

Mendel's Discovery

Gregor Johann Mendel an Austrian Augustinian Monk born in 1822 to peasant parents.

Mendel did an experiment on pea plants (pisum sativum) where it was not understood until early 1900s.

Mendel gain the title of “the father of genetics” for his discovery

Mendel’s Experiment

He used 22 varieties of peas and after the self pollination, the offspring are like the parent plants.

He cross pollinated the varieties for his experiment.

He followed the inheritance of individual traits, he gathered statistical data and used his understanding of mathematical laws of probability to interpret the results.

Studied the inheritance of relatively distinguishable traits, seed shape, seed color and flower color.

Mendel's Result and Findings

1. When he crossed purple-flowered plants with white-flowered plants, the F1 generation offspring all had purple flowers.

2. When F1 offspring mature and self-pollinate, some F2 offspring had white flowers.

3. The traits he studied did not produce intermediate types when crossed instead, alternatives were inherited as distinct characteristics that were either seen in a particular generaton.

4. One trait individual does not appear in the F1 hybrid, but reappear in the F2 hybrid.

5. Pairs of trait segregated among offspring

6. According to Mendelian ratios, the F2 generwtion had ¾ Dominant and 1/4 recessive.

Mendelian's interpretation

Parents do not transmit physiological trait or function but rather factors that later act in the offspring to produce trait.

Each parent contain two factor (homo and heterozygous).

Two alleles contributed by male and female; they do blend or affect each other.

When the offspring mature and produce its own gamete, these gametes contain the equal proportion of element as the parent.

Mendel's Conclusion

• 1st law: Law of Segregation - each organisms contain two factors for each trait. One of these factors can be passed onto the gamete during its formation. Offspring have exactly one factor for each trait, Each one from both the parents.

• 2nd law: Law of Independent Assortment - one pair of factors segregate independently of another pair of factor. Each trait have their own specific location in the chromosome.

• 3rd law: Law of Dominance - the dominant trait will always be expressed as long as it is present. The other will be masked out (recessive) and will only be expressed with the absence of dominant trait.