Genetics in History

Gregor Johann Mendel Scientist and Friar; conducted experiments on pea plants from 1856 – 1863 Established the rules of heredity, now known as the laws of Mendelian inheritance Tested 7 characteristics of pea plants: plant height, pod shape and color, seed shape and color, and flower position and color

Why did Mendel pick Garden Peas? Garden peas reproduce sexually Garden peas can self-pollinate He could control traits while still allowing for random selection Mendel was a good scientist He recorded accurate data He only tested one trait at a time

The first trait Mendel tested was height, and it resulted in hybrids. Hybrid: offspring that has different forms of the trait. (Tt) than its parents (TT x tt)

First Generation Second Generation He cross-pollinated tall pea plants with short pea plants. Mendel found that All the pea plants grew to be tall The short trait had disappeared He allowed first generation to self-pollinate. Planted the seeds from the self-pollination. Grew 1000 plants

Mendel discovered that: ¾ were as tall as the parent plants ¼ were short like the parent generation. They occurred in a ratio of 3:1 The short trait reappeared out of nowhere. Each trait tested had the same 3:1 ratio!

P1 Generation F1 Generation F2 Generation The original parent or the true breeding plant. F1 Generation The offspring of the parent (P1) F2 Generation The offspring of the (F1) generation. P = Parental (first generation of controlled mating) F = Filial (each generation resulting from a controlled mating)

Compare this to your family: P1 generation – Your Grandparents F1 generation – Your Parents F2 generation – You F3 generation – Your Offspring

The Rule of Unit Factor Alleles – Alternate form of the same gene, or traits. Each pea plant had two alleles that determined its height, color, shape, etc…

An organism’s alleles are located on two different copies of a chromosome. One is inherited from the male parent One is inherited from the female parent

The Rule of Dominance Dominant trait: Recessive trait: The trait that shows up ¾ of the time. Shown with uppercase letters ~ TT, Tt Recessive trait: The trait that shows up ¼ of the time. Shown with lowercase letters ~ tt

Every individual has two alleles of each gene. After meiosis, The Law of Segregation Every individual has two alleles of each gene. After meiosis, Sperm cells have one allele for a trait Ovum cells have one allele for a trait When combined at fertilization you have two alleles for each trait.