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

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

3. 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

4. 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

5. 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
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.

9. 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.

10. 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

11. 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.

12. 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