Mendel and Heredity Genetics: The study of heredity -what characteristics get passed on, and how are they passed on? Heredity: The transmission of characteristics from one generation to the next.

Origins of Genetic Science Gregor Mendel ( ) -Augustinian Monk, designed experiments to see if environment or “something else” influenced the traits of organisms.

Mendel published his work on genetics in 1866, but it was largely ignored until His work was finally recognized as an important part of genetic research. Why was Mendel’s work ignored? Why was his work finally recognized?

Mendel worked with large numbers of pea plants. -peas reproduce sexually, recombining genes -easy to grow in large numbers -many traits expressed on 1 plant Benefits of using pea plants:

Generations Parental Generation (P) First Filial Generation (F1) Second Filial Generation (F2)

Mendel’s Early Experiments -the result was plants, all with smooth seeds (F1 generation) -crossed peas with smooth seeds and peas with wrinkled seeds (PxP cross)

RR rr Rr Smooth Peas Wrinkled Peas Smooth Peas P F1

Mendel then crossed F1 plants with F1 plants The result was a ratio of 3 plants that produced smooth peas to 1 plant that produced wrinkled peas. Rr x Rr

-For every trait, there are 2 factors, one from the male, one from the female. -(we now call the “factors” genes.) The combination of these factors determines the trait that is expressed. Mendel’s Hypothesis:

Mendel represented dominant genes with a CAPITAL letter, and recessive genes with a lower case letter. Ex: R for Round, smooth peas r for wrinkled peas

Terms: Allele: One of two or more alternate forms of a gene. Example: R - round seeds r - wrinkled seeds

Genotype: The combination of alleles that an organism has. Example: in peas, for seed shape, the possible genotypes are RR, Rr, and rr. Phenotype: The physical or visible features determined by the organisms genotype: Example: round peas, blue eyes, tallness

Homozygous: When an organism has 2 identical alleles for a trait Example: RR or rr Heterozygous: When an organism has 2 different alleles for a trait Example Rr Homozygous Dominant (RR) Homozygous Recessive (rr)

Mendel’s 2 Laws: 1) Law of Dominance- One form of a hereditary trait, the dominant trait, dominates or prevents the expression of the recessive trait.

2) The Law of Segregation: During gamete formation, the pair of genes responsible for each trait separates so that each gamete receives only 1 gene for each trait.

Punnett Squares -allow us to predict the outcome of the combination of possible gametes A A A a AA Aa Gametes

Incomplete Dominance -three phenotypes result, with the third being intermediate to the other two -neither allele is dominant to the other

Example: In some flowers, the alleles for flower color show incomplete dominance. The allele for RED is R, the allele for WHITE is W. The resulting cross of 2 homozygous individuals would be: RR x WW

RR x WW (PxP cross) RR W W RW RR= Red Flowers WW= White Flowers RW= Pink Flowers F1

RW x RW(F1xF1 cross) RW R W RRRW WW RR= Red Flowers WW= White Flowers RW= Pink Flowers F2

Crosses with 2 traits EX: Tall/Red x short/white Parent Genotypes: TTRR x ttrr T= Tall t = short R=Red r= white Both are homozygous

Things to remember: 2) gametes MUST have one allele for each trait. 1) alleles for traits always sort independently.

TTRR x ttrr (P x P cross) Possible Gametes: TR Possible Gametes: tr

TR tr Possible Gametes TtRr

F1 cross (TtRr x TtRr) TtRr Possible Gametes: TR Tr tR tr Possible Gametes: TR Tr tR tr TtRr

TR Tr tRtr TR Tr tR tr TTRR TTRr TtRRTtRr TTRrTTrrTtRrTtrr TtRR TtRr ttRR ttRr TtRrTtrrttRrttrr

Codominance -But it is different, because instead of an intermediate trait, being shown, both traits are exhibited. -Codominance is similar to incomplete dominance, because neither allele is dominant to the other.

Example: Blood types Type A Type B Type AB Type O

There are 3 alleles for blood type. A,B,and O A and B are codominant O is recessive to both A and B Phenotype A B AB O Genotype AA, AO BB, BO AB OO

AO x AB AO A B AA AO AB BO

AO x BO AO B O AB BO AO OO