The Work of Gregor Mendel
Chapter 11 Section 1
Notes
Who was Gregor Mendel?
Austrian Monk (1822 - 1884) “Father” of modern genetics (the science of heredity) Bred pea plants to study inheritance of traits Taught high school science
Why was Mendel so Successful?
Began with “truebreeding” (purebred) plants Kept detailed records Followed scientific method Used math to confirm his scientific findings
What did Mendel Do?
Cross bred pea plants Studied 7 traits (characteristics), one variable at a time Studied only traits easy to see or measure Removed male or female flower parts to ensure which plants bred together
Genetics Vocabulary
Genes – piece of a chromosomes that codes for a protein, determining a trait. Allele – different forms of a gene Genotype – combination of alleles for a trait Phenotype – physical appearance – the expression of the alleles present
Vocabulary continued
Homozygote – organism with 2 identical alleles for a trait.
Homozygous – describes being a homozygote Purebred
Heterozygote – organism with 2 different alleles for a trait.
Heterozygous – describes being a heterozygote hybrid
Vocabulary continued
P generation – the parental generation – beginning of genetic study – true breeding F1 generation – 1st offspring generation (F = Filius = son) F2 generation – 2nd offspring generation originating from the F1
Parent generation – true breeding
1st offspring generation – hybrid
2nd offspring generation – variety
Mendel’s Experiment
Began with true-breeding plants (P generation) Studied one trait at a time Discovered that all the F1 showed only one trait. Example: Pure breeding tall crossed with pure breeding short produced all tall F1.
Mendel’s Experiment
Mendel allowed F1 to self-pollinate. Discovered that the allele which “disappeared” in the F1 generation reappeared in the F2 Only ¼ of the offspring showed the allele
Example: Self-fertilizing F1tall plants produced ¾ tall plants and ¼ short plants
Dominant
Characteristics that appeared in the entire F1 generation and 75% of the F2 or “second filial” generation Expresses its effect even in presence of another allele for the trait
Recessive
Characteristics that did not appear in the F1 generation, but reappeared in 25% of the F2 generation Allele is not expressed in presence of a dominant allele = Mendel’s “Principle of Dominance”
Mendel’s Law of Segregation
Every individual carries a pair of alleles for each trait The members of the pair separate during the formation of gametes What process do we now know that this describes? Meiosis! Mendel discovered the outcome of this process without ever seeing it in action!