Opener: Get out a clean piece of paper and Title it: #47 Mendel Notes HAND COPY AND RETURN!!! 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.

Ex: ‘t’ – represents the allele for short plants 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.

Friday’s Quiz: Vocab: A Pea Plant Test Cross 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