Download Genetics

Genetics
Genetics is the study of heredity or the passing of traits from an organism to its offspring.
Austrian monk, Gregor Mendel performed some of the first genetics work with pea plants
in the 1860s.
1. He realized that some traits (characteristics) were passed on from one generation
to another.
2. Mendel realized that each organism could pass different traits to their offspring.
3. These traits are controlled by genes.
Genes are the units of heredity.
Genes are expressed in an organism as traits.
There are two types of traits, dominant traits and recessive traits.
The basic principles of genetics are:
1. Traits are passed on from one generation to the next.
2. The traits of an organism are controlled by genes.
3. Organisms inherit genes in pairs, one gene from each parent.
4. Some genes are dominant, whereas some genes are recessive.
5. Dominant genes hide recessive genes when both are inherited by an organism.
An organism with genes that are the same for a trait are called purebreds.
An organism with genes that are different for the same trait are called hybrids.
Phenotype refers to a visible characteristic of an organism. This is the physical
appearance of the organism.
Genotype is the actual genetic make up of an organism.
Probability can be used to predict the results of genetic crosses. Punnett squares are used
to calculate the probability of an organism’s phenotype and genotype.
Genotypes are expressed as letters for example:
1. Hair color may be expressed as the letter B for black, and b for blonde.
2. Each genotype will have at least two letters. Capital letters represent the
dominant trait, and lower case letters represent the recessive trait. The dominant
trait in a genotype is always expressed over the recessive trait. For example
consider the following genotypes:
a. BB and Bb genotypes would express the phenotype of black hair.
b. Only bb genotypes would show the phenotype of blonde hair.