Who is this man?

That was Gregor Mendel, the “Father of Genetics”. He was a scientist and a monk who lived in the 19th century in Austria. He became interested in the different characteristics of plants, specifically pea plants. Why did some have white flowers and others purple flowers? Why were they different heights? Why were some seeds smooth and other wrinkled?

After years of work, Mendel discovered that these traits are inherited from the parents.

Heredity is when traits are passed from parent to child. Heredity is controlled by genes. Every organism that is produced through sexual reproduction has two genes for each trait. One of these genes comes from the mother and one from the father. Genes may have different forms. The different forms a gene may take are called alleles.

Some genes are dominant. Other genes are recessive. Dominant genes will cover up or hide recessive genes. For example, humans can be either left or right-handed. This is an inherited trait. Right-handedness (R) is dominant, while left-handedness (r) is recessive. If a person has two genes, RR, which hand will they write with? What if their two genes are Rr? Or rr?

Recessive traits are expressed less frequently. Some diseases are termed “recessive genetic disorders”. Ex.- cystic fibrosis, sickle cell anemia They are inherited from the parents, but an individual must inherit two recessive alleles.

These possible combinations can be shown in a Punnett Square. For example, if this refers to tall vs. short pea plants, you can see possible outcomes of the offspring. What percentage of offspring will be tall? Short?

Genotype - the genetic make-up of an organism; ex. Tt or Bb Phenotype - the physical appearance of the organism based on the genotype; ex., tall or brown Homozygous - has identical alleles for a trait; ex. TT or tt Heterozygous - has two different alleles for a trait; ex. Tt

In this example, both parents are heterozygous for the trait. If R = red flowers and r=white flowers, which is dominant? What percentage of the offspring from this cross are expected to have red flowers? White flowers? What is the phenotype of a Rr flower?

What makes some of us male and some of us female? A child’s sex is determined by one pair of chromosomes (23rd pair). Females have XX. Males have XY. The mother’s eggs all contain one X chromosome. The father’s sperm may contain either an X or a Y chromosome. Let’s try a Punnett Square to determine the probability that a child will be male or female.

Some traits may be on either the X or Y chromosome. These are called sex-linked genes.

Why is the study of genetics so important? 1. Can prevent or cure diseases 2.. Genetic engineering ( finding ways to change a DNA sequence) 3. Designing new traits in plants 4. Human genome project