Mendelian Genetics Gregor Mendels research Mendel proposed the

Mendelian Genetics Gregor Mendel’s research

• Mendel proposed the first theory about the units of inheritance (what we now call genes) and described two fundamental rules governing how traits are inherited. • Mendel’s work is recognized today as one of the greatest breakthroughs in the history of science.

• In one experiment he made a cross between two true-breeding strains, one with wrinkled seeds and another with round seeds. • This is called a monohybrid cross because the two plants involved in the cross differ only in one character (in this case, seed shape).

• The plants involved in the original cross are called the parental or P generation. In this experiment, Mendel found that all the progeny plants, the first filial or F 1 generation, produced only round seeds. The wrinkle trait seemed to have been masked, or “dominated, ” by the round trait in the F 1 seeds.

• Mendel called the round trait dominant and the wrinkled trait recessive. All seven monohybrid crosses behaved in a similar manner; they produced F 1 progeny processing the trait of one of the parents. • Mendel then planted the F 1 seeds for each cross, raised the plants, and allowed them to self pollinate to produce the second filial or F 2 generation. • He found that both dominant and recessive types appeared in the F 2 generation in a numerical ratio of 3 dominant to 1 recessive.

• Mendel proposed that genes exist in different forms and can consequently give different traits. • Today we call different forms of one gene an allele.

Autosomal Dominant • If the trait were dominant, we would use the following designations: A = the trait (a genetic disease or abnormality, dominant) a = normal (recessive)

Autosomal Recessive • If the trait were recessive, we would use the following designations: A = normal (dominant) a = the trait (a genetic disease or abnormality, recessive)

X-linked Recessive • We use the following symbols for X-linked recessive: XA = normal Xa = the trait (a genetic disease or abnormality) Y = Y chromosome (males only)

Rr rr

XA XA XA Xa XA Y Xa Y* * = trait is expressed

Assignment • Pg. 178, Section 1 Review 1 -7 • Due on Wednesday (1/15)