Mendel GeneticsCh 5.

Crash course Biology: Heredity https://www.youtube.com/watch?v

=CBezq1fFUEA&list=PL3EED4C1D684D3ADF&index=9

Need to know Terms Homozygous - is used to describe the genotype

of an organism that has two alleles that are the same. For example, in Mendel's first cross, he used a homozygous round seed (RR) plant and a homozygous wrinkled seed (rr) plant.

Heterozygous - is used to describe the genotype of an organism that has two different alleles. For example, the offspring produced in the F1 generation were heterozygous (Rr).

Monohybrid Cross - a cross involving only one trait. For example, in Mendel's first cross he only looked at seed shape.

Dihybrid Cross - a cross involving two traits. For example, crossing a tall, purple plant with a short, white plant.

Need to know Terms Phenotype is the term used to describe

physical characteristics. Alleles - alternative forms of a specific

trait, (ex. Tall/short or round/wrinkled)

Gregor Mendel Augustinian Monk who had an interest in

nature, plants and evolution. While assigned to teach high school science, he began his experiments with pea plants. Mendel worked on the blending theory of heredity which was widely accepted among researchers. His work in this area fostered a new understanding of heredity which provides the bases for genetics. Mendel chose to work with pea plants for three reasons

Why Pea Plants?1. Pea plants have many physical

characteristics that are expressed in one of two ways: dominant or recessive. Phenotype is the term used to describe physical characteristics.

The table on the next slide describes the phenotypes Mendel used in his experiments.

Why Pea Plants? The trait is shown in the first column

and the alternative forms of the trait, called alleles, are listed in the second and third columns respectively.

Trait Dominant Recessive

Flower Color Purple White

Pod color Green Yellow

Seed color Yellow Green

Seed shape Round Wrinkled

Pod shape Inflated Constricted

Flower position Side of stem End of stem

Stem length Tall Short

Why Pea Plants?2. Pea plants can either self-fertilize or

cross-fertilize. He chose to artificially cross-fertilize plants which were pure bred. That is they always produced the same type of offspring. Using a fine brush, Mendel would transfer the pollen from one plant to another and observe the characteristics in the developing seed.

Why Pea Plants? The image below illustrates the stamen; this is

the male part of the flower that releases pollen. Also shown is the ovary, which is the female part of the flower that contains the egg cells.

Why Pea Plants?3. Pea plants grow easily and mature

quickly and produce many seeds.

In Mendel's experiments, only plants that consistently produced the same trait for multiple generations were used. Mendel took the pollen from a plant that produced round seeds and crossed it with the eggs of a plant that produced wrinkled seeds. He called this generation, the parent generation (P).

When he observed the offspring he noticed that all the seeds were round. Mendel referred to this generation as the first filial or F1 generation.

To keep track of all his crosses, Mendel devised a system of letters to represent specific traits. For example, a capital letter is used to represent a dominant trait and a small case letter is used to show a recessive trait.

Mendel used a chart, called a Punnett square, to organize his results. The chart is helpful to predict the possible phenotypes of the offspring produced.

The chart resembles an X and O table. The male gametes are arranged in the top spaces and the female gametes are aligned along the sides.

Punnett’s square