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Opener: Get out a clean piece of paper and Title it: #47 Mendel Notes 1) Find your 3:00 Buddy 2) Using your textbook answer the following: 1) What did.

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Presentation on theme: "Opener: Get out a clean piece of paper and Title it: #47 Mendel Notes 1) Find your 3:00 Buddy 2) Using your textbook answer the following: 1) What did."— Presentation transcript:

1 Opener: Get out a clean piece of paper and Title it: #47 Mendel Notes 1) Find your 3:00 Buddy 2) Using your textbook answer the following: 1) What did Gregor Mendel do?

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

3 I. Mendel’s Experiments A.Crossing Pea Plants 1.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

4 II. Dominant and Recessive Alleles A. Mendel determined that each trait exists in pairs (one coming from each parent). B. Genes and Alleles 1. Gene – factors that control a trait 2. 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

5 3. 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

6 Dominant and Recessive Alleles in Pea Plants

7 Dominant Allele Recessive Allele

8 III. Mendel’s Results A. Fertilization 1. First Cross  The two purebred “parents” were crossed and all of the offspring were tall. 2. 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.

9 B. Alleles in Mendel’s Crosses 1. Homozygous tall plants had two alleles for tall stems. 2. Homozygous short plants had two alleles for short stems. 3. A hybrid organism is one that is heterozygous for a trait.

10 C. Symbols for Alleles 1. A dominant allele is represented by a capital letter. Ex: ‘T’ – represents the allele for tall plants 2. A recessive allele is represented by a lowercase letter. Ex: ‘t’ – represents the allele for short plants 3. Possible allele combinations are written as follows: TT = Homozygous Tall Plant Tt = Heterozygous Tall Plant tt = Homozygous Short Plant

11 D. Significance of Mendel’s Contribution 1. Before Mendel, traits were thought to be a blend of the parents. 2. Mendel’s experiments showed that traits don’t always blend.

12 Friday’s Quiz: 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


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