Ch. 11 Intro to Genetics

11-1 The Work of Gregor Mendel

1. Gregor Mendels’ Peas Peas in a Pod Purple & White Flowers on Pea Plants

Genetics- the scientific study of heredity Mendel was an Austrian monk who wanted to understand genetics. Mendel studied pea plants to improve his understanding of how traits are passed from parents to offspring.

Video: Mendel’s Experiment

What did Mendel Know Before His Experiments? the male part of each flower produces pollen, (containing sperm). the female part of the flower produces egg cells.

Fertilization- union of an egg and sperm cell resulting in a new cell during sexual reproduction Self-Pollinating-Sperm cells in pollen fertilize the egg cells in the same flower Pea flowers are self-pollinating The seeds that are produced by self-pollination inherit all of their characteristics from the single plant that bore them.

The Experiment: True-Breeding- occurs when plants produce offspring identical to themselves after self-pollination Mendel’s pea plants were true-breeding as a result of self-pollination. Cross-Pollination- when pollen from one flower is delivered to a flower from a different plant. Mendel used cross-pollination to produce seeds that had two different parents.

He cut away the pollen-bearing male parts of the plant and dusted the plant’s flower with pollen from another plant.

2. Genes & Dominance

Trait- a characteristic that is different in each individual Ex: the puppy has a trait for brown fur Mendel studied pea plants with 7 different contrasting traits. Ex: white flower x purple flower, tall x short, etc. These plants were crossed & he studied their offspring.

The original parents are represented by P (parental) The offspring of the original parents are called the F1 generation (1st filial) The offspring of the F1 generation are called F2 generation (2nd filial) Hybrid- The offspring of crosses between parents with different traits Ex: the offspring of a cross b/w a red rose & white rose. The term “crossing” means mating

Results of Mendel’s exp. Crossing parents w/ contrasting traits:

The result: all offspring had only one of the parents characters

Alleles- a different form of a gene. The conclusion: some alleles are dominant and others are recessive biological inheritance is determined by genes Genes – the basic units of heredity that are passed from one generation to the next. Alleles- a different form of a gene. Ex: A gene for height, with two alleles tall and short.

Principle of Dominance- some alleles are dominant some are recessive. The dominant allele is always expressed Ex: a cross b/w a black horse and a white horse; all of the offspring have black fur. The recessive allele is only expressed when the dominant allele is absent. Ex: a cross b/w two white mice; all of the offspring have white fur.

3. Segregation

Segregation- the separation of alleles from each other. Mendel self-pollinated the F1 generation. The results were some traits only appeared in 1/4th of the F2 generation.

Mendel’s F2 Generation Mendel assumed the dominant allele masked (hide) the recessive allele’s presence in the F1 generation.

Gametes- Sex cells; egg cells & sperm cells Each F1 plant produces two types of gametes—those with the allele for tallness, and those with the allele for shortness.

Alleles separate during gamete formation. alleles separate from each other so that each gamete carries only a single copy of each gene.