Opener: Get out a clean piece of paper and Title it: #47 Mendel Notes

Opener:Get out a clean piece of paper and Title it: #47 Mendel Notes • Find your 3:00 Buddy • Using your textbook answer the following: • What did Gregor Mendel do?

Prime Time Answers… • Gregor Mendel experimented with pea plants to determine how parents pass traits to their offspring.

I. Mendel’s Experiments • Crossing Pea Plants • Mendel decided to cross purebred pea plant with contrasting traits a. ex: crossing tall plants with short plants b. Purebred – an organism which is homozygous for a trait

II. Dominant and Recessive Alleles A. Mendel determined that each trait exists in pairs (one coming from each parent). B. Genes and Alleles • Gene – factors that control a trait • Alleles – the different forms of a gene • ex: The gene that controls stem height in pea plants has two different alleles; one for tall plants and one for short plants

An organism’s traits are controlled by the alleles it inherits from its parents. Some alleles are dominant and some are recessive. • Dominant Allele – the allele whose trait always shows up in the organism when the allele is present • Recessive Allele – the allele that is hidden whenever the dominant allele is present

Dominant and Recessive Alleles in Pea Plants

Dominant Allele • Recessive Allele

III. Mendel’s Results A. Fertilization • First Cross • The two purebred “parents” were crossed and all of the offspring were tall. • Second Cross • The offspring of the first cross were crossed with each other and Mendel noticed that about ¾ were tall and ¼ were short.

Alleles in Mendel’s Crosses • Homozygous tall plants had two alleles for tall stems. • Homozygous short plants had two alleles for short stems. • A hybrid organism is one that is heterozygous for a trait.

Symbols for Alleles • A dominant allele is represented by a capital letter. Ex: ‘T’ – represents the allele for tall plants • A recessive allele is represented by a lowercase letter. Ex: ‘t’ – represents the allele for short plants • Possible allele combinations are written as follows: TT = Homozygous Tall Plant Tt = Heterozygous Tall Plant tt = Homozygous Short Plant

Significance of Mendel’s Contribution • Before Mendel, traits were thought to be a blend of the parents. • Mendel’s experiments showed that traits don’t always blend.

Vocab: Allele Gene Genetics Fertilization Trait A Pea Plant Test Cross Essay question about why recessive traits cannot be hybrids. Hybrid Purebred Heredity Recessive Allele Dominant Allele Friday’s Quiz:

Opener: Get out a clean piece of paper and Title it: #47 Mendel Notes