Download Notes on The Basics of Genetics Part 1

The Basics of Genetics
GREGOR MENDEL: Father of Genetics
1. Traits are passed or inherited from one generation to the next.
2. Traits of an organism are controlled by genes.
A gene is a section of a chromosome, that codes for a specific trait.
3. Organisms inherit genes in pairs, one from each parent.
*Human sex cells (sperm or egg) contain 23 chromosomes each.
*When the egg is fertilized, the new baby will have 46 chromosomes in each of its
cells, which is the correct number of chromosomes for a human.
4. Some genes are dominant, while others are recessive.
*“Stronger” traits are called dominant.
*“Weaker” traits are called recessive.
Geneticists use symbols (letters) to represent the different forms of a gene.
Dominant traits are represented by a capital letter.
Yellow seeds are dominant……..
Y
Recessive genes (for the same trait) are represented by THE SAME lower case
letter.
Green seeds are recessive……….
y
Dominant (yellow) = Y
Recessive (green) = y
*In pea plants, tall is dominant over short. The letter used to represent the tall gene
is T.
*The short gene is represented by t.
5. Dominant genes hide recessive genes when both are inherited by an organism.
Y + y = yellow seeds (yellow is dominant)
T + t = tall plant (tall is dominant)
B+ b = brown eyes (brown is dominant)
A PUREBRED organism has two of the same genes for a trait.
TT = purebred TALL
tt = purebred SHORT
A HYBRID organism has two different genes for a trait.
Tt = hybrid TALL (tall is dominant.)