The Work of Gregor Mendel I Historical Views

The Work of Gregor Mendel

I) Historical Views A) Blending Theory A) Mixture of sperm & egg resulted in progeny that were a "blend" of two parents' characteristics B) Ignored characteristics that skipped generations-FLAW

II) Gregor Mendel “Father of Modern Genetics” A) His ideas form the backbone of modern genetics B) Most pea plants self-pollinate

II) Gregor Mendel C) He started with true-breeding pea plants 1) If allowed to selfpollinate, they produce identical offspring to parent

II) Gregor Mendel D) Cross-Pollinated plants for experiment E) He studied 7 different traits 1) A specific characteristic, such as seed color or height

The 7 traits Mendel studied Seed Shape Seed Color Seed Coat Pod Color Shape Pod Color Flower Position Tall Axial Round Yellow Gray Smooth Green Wrinkled Green White Constricted Yellow Round Yellow Gray Smooth Green Plant Height Short Terminal Tall Axial

II) Gregor Mendel F) Called each starting plant the parent (P) G) Crossed plants with differing traits , resulting in offspring (F 1) 1) F 1 crosses between parents of different traits were hybrids

Principles of Dominance P Generation Tall Go to Section: Short Tall Tall Short

Principles of Dominance P Generation Tall Go to Section: Short F 1 Generation Tall Tall Short

The 7 traits Mendel studied Seed Shape Seed Color Seed Coat Pod Color Shape Pod Color Flower Position Tall Axial Round Yellow Gray Smooth Green Wrinkled Green White Constricted Yellow Round Yellow Gray Smooth Green Plant Height Short Terminal Tall Axial

III) Mendel’s Conclusions A) Inheritance is determined by factors that are passed from one generation to the next 1) Today these factors are called genes 2) Alleles: Different forms of a gene B) Principle of Dominance 1) Some alleles are dominant, and others are recessive 2) Need only one dominant allele to see that trait (TT or Tt both tall) 3) Must lack any dominant alleles to see the recessive trait (only tt is short)

IV) Principle of Segregation A) What happened to the recessive traits? B) Mendel crossfertilized the F 1 plants, resulting in F 2 offspring with some recessive alleles reappearing

IV) Principle of Segregation C) Alleles for a gene are segregated from each other during the formation of gametes

Principles of Dominance & Segregation P Generation Tall Go to Section: Short F 1 Generation Tall Tall Short

Mendel Observed the Principles of Dominance & Segregation Section 11 -1 P Generation Tall Go to Section: Short F 1 Generation Tall F 2 Generation Tall Short

V) Probability A) The likelihood that a particular even will occur B) Can be used to predict the outcome of a particular genetic cross C) Used to predict averages, not precise numbers D) Use a tool called a Punnett Square

Punnet Squares: Why did Mendel obsereve what he did? COPY THIS

Notice all of the results are around a 3: 1 ratio

VI) Genetics Key Terms A) Homozygous - when the two alleles are the same. B) Heterozygous - when the two alleles are different, in such cases the dominant allele is expressed

V) Genetics Key Terms C) Genotype- genetic make-up. D) Heterozygous – physical characteristics