The Work of Gregor Mendel Chapter 11.1 The Work of Gregor Mendel

Every living thing has characteristics that are passed down from parent to offspring. Genetics is the scientific study of heredity. Scientists have wanted to understand how traits are passed and how they make each species unique.

Gregor Mendel’s Peas Gregor Mendel was an Austrian monk who started work with garden peas to see how traits were passed on. Fertilization is when egg cells join with sperm cells to make a new organism. Pea plants are usually self-pollinating, meaning that the plant produces egg and sperm and they undergo fertilization to make a new pea plant. A self-pollinating plant will pass on all of it’s characteristics to it’s offspring. Another name for self-pollinating plants are true-breeding.

In Mendel’s first experiment he took a true-breeding tall plant and a true-breeding short plant and crossed them. He did this by dusting pollen from one plant onto the flower of another plant – this is called cross- pollination. He was able to control which plants he was crossing this way.

Genes and Dominance Mendel looked at 7 different traits in pea plants. A trait is a specific characteristics like seed color or plant height that varies from one individual to another. Every trait Mendel studied had 2 different characteristics for the same trait. He had a parent generation and the generation they produced (their offspring) was called the F1 generation. The F1 generation were hybrids – a cross between 2 parents with different traits.

In the F1 generation all the offspring had the characteristics of only 1 of the parents. For example when he crossed a tall and short plant he got all tall plant offspring.

Mendel discovered 2 things: 1. Inheritance is determined by factors that are passed from one generation to another – these factors today are called genes. For each trait Mendel studied there were 2 forms of the same trait (like tall and short). These different forms of the same gene are called alleles. 2. Principle of dominance – some alleles are dominant and others are recessive. That mean that if the dominant allele is present it will show up no matter what. The only way for a recessive allele to show is for the dominant allele to be absent. In the tall and short example the dominant trait was tall.

Segregation Mendel wanted to know if the recessive trait was still present in the offspring or did it disappear. To figure this out he allowed the F1 generation to self-pollinate. This produced the F2 generation.

The F1 Cross In the F2 plants the recessive allele reappeared. He found that ¾ were still tall and ¼ was short.

Explaining the F1 Cross Mendel decided that for the recessive gene to reappear it had to separate, or segregate, from the dominant gene. He realized that during the formation of gametes, or sex cells (egg and sperm), the 2 alleles separated. He found that in the F1 generation the parent produced 2 different gametes those with the dominant allele and those with the recessive. Don’t worry – I will explain this in class!