Genetics Biology I The Science of Heredity The

Genetics Biology I

The Science of Heredity • The scientific study of heredity is called GENETICS

Gregor Mendel Father of genetics

Gregor Mendel- The Man Personal history 1. Austrian monk 2. Teacher of high school natural science- lover of evolution, nature, meteorology 3. Crossed pea plants and saw inheritance patterns

Gregor Mendel Pea Plant Experiment • Gregor Mendel chose pea plants to conduct genetic experiments because of their plant life special properties. For example: • When pollen fertilizes an egg cell, a seed for a new plant is formed. (Pollen is plant sperm cells) • Pea plants normally reproduce by selfpollination.

Gregor Mendel Pea Plant Experiment • To perform his experiments, how did Mendel prevent pea flowers from self-pollinating and control their cross-pollination? He cut away the pollen-bearing male parts of a flower and dusted that flower with pollen from another plant.

Gregor Mendel Pea Plant Experiment • What does it mean when pea plants are described as being true-breeding? If the plants are allowed to self-pollinate, they would produce offspring identical to themselves.

Vocabulary • Traits - Specific characteristics that vary from one individual to another • Hybrids-The offspring of crosses between parents with different traits • Genes - Chemical factors that determine traits • Alleles - The different forms of a gene

Trait • Consist of 2 alleles For example: BB or Bb or bb • Alleles come in two forms: DOMINANT- Capital letter recessive – Lower cased letter • If a trait has 2 recessive alleles, then the traits is recessive. bb, aa, ff • If a trait has one dominant allele then the trait is dominant. Bb, BB

Traits • If both alleles are the SAME then the trait is homozygous. BB, bb, NN, nn • If the alleles are DIFFERENT then the trait is heterozygous. Bb, Nn, Gg • BB- homozygous dominant • bb- homozygous recessive • Bb- heterozygous dominant

Steps of Mendel's Experiment

1. Mendel studied the inheritance of one trait (for example a plant's height, color of flowers, seed color, and shape of seeds).

A cross in which only ONE contrasting trait is studied is called a monohybrid cross. Only one alphabet can be used. For Example: Tall – TT or Tt Short - tt ONLY THE LETTER T IS USED.

2. Mendel first cross pollinated tall pea plants with each other. (TT) T TT TT TT

In every generation of this plant, only tall plants were produced.

3. Mendel then cross pollinated short pea plants with each other. (tt) t tt tt tt

X

In every generation of this plant, only short plants were produced.

The next step of Mendel's experiment was to crossed tall pea plants (TT) with short pea plants (tt). T t Tt Tt

He then crossed two pea plants which contained both tall and short alleles. T t T TT Tt tt

¾ of the pea plants were tall, ¼ were short.

Mendel named every generation: 1) Starting generation P (parent) generation. 2) first generation F 1 generation (offspring of the P generation) 3) second filial generation F 2 generation (offspring of the F 1 generation)

P F 1 F 2

Genotype vs. Phenotype • Physical characteristic of an organism • Example: tall or short Genotype • Genetic makeup of an organism • Example: Tt or TT or tt