Mendel and His Discoveries Chapter 11 Gregor Mendel

Mendel and His Discoveries Chapter 11

Gregor Mendel l Gregor Mendel (1822 -1884) Experimented with pea plants and developed fundamental rules of genetics and patterns of inheritance.

Punnett Squares l l Crosses between parents that differ in only one trait are called MONOHYBRID CROSSES. P= Parents F 1= First Filial generation (kids) F 2= Second Filial generation (grandkids)

Mendel and Pea Plants l l For his plant experiment he crossed a tall plant with a short plant. All of the offspring looked tall. Why? Because the tall plants had a dominant trait and the short plants had a recessive trait.

Alleles l Alleles are simply versions of genes THE ALLELES FOR COW FUR COLOR ARE BLACK. BROWN, AND WHITE

Prediction of Genetic Crosses l The alleles for tallness of a plant: l l l TT= Dominant (Tall) tt= Recessive (Short) How do we know for sure that they would all be tall? l The Punnet Square

Punnett Squares l l l Tool to predict outcomes of genetic crosses Make a tic-tac-toe board Place the parent alleles like below: TALL PARENT PLANT SHORT PARENT PLANT

Let’s try another one… l l l If the trait is for feather color of parrots, then GG= Dominant and is green. gg= recessive and is gold. GG allele is homozygous dominant; (Homo- same; zygous-sex cell; dominant- dominant)

l l gg allele is homozygous recessive; (Homo- same; zygous- sex cell; recessive- recessive) So from the cross above we get all Gg. So are they Green or gold or a mix of both?

l l They are all green. Gg is called heterozygous. Heterozygous means different. If a G and a g are together to make a heterozygous trait, the trait looks like the dominant gene or G. So, ALL the parrots look green.

But what about the KIDS of these new, green parrots? l Genetics of the new, GREEN (F 1) parrots: l G Gg x Gg g G GG Gg gg

Ratios? l l Phenotype: the “look” of the genes Genotype: the “letters” or alleles of the organism PHENOTYPE RATIOS: 3: 1 GENOTYPE RATIOS: 1 GG, 2 Gg 1 gg

Why we needed the math: The Dihybrid Cross l Lets say that in peas, We cross a Homozygous dominant Smooth, yellow seed with a Homozygous recessive wrinkled, green seed. What would be the genotype and phenotype of the F 1 generation?

Setting it up l SS= Smooth ss= wrinkled l So we are crossing a SSYY x ssyy l YY= yellow yy= green

Ready, set, go! l Most important question: What are all of the possible sperm and egg that each plant can produce with those alleles? (huh? ) SSYY Plant ssyy Plant SY sy

l The product of this cross will all be: Ss. Yy, or all Smooth, Yellow peas (F 1) l But what about the F 2 generation? l

Ask the Important Question again! l Most important question: What are all of the possible sperm and egg that each plant can produce with those alleles? SY Ss. Yy Sy s. Y PEA SEED sy

9: 3: 3: 1

Incomplete Dominance l What do you get when you cross a homozygous dominant red rose with a homozygous white rose?

Incomplete Dominance l l A Pink Rose! Since all of the F 1 are Rr= pink, what would be the F 2 generation of all of the F 1 pink roses?

1 Red: 2 Pink: 1 White R r R RR Rr rr

Codominance l Codominance- when both alleles contribute to the phenotype of the organism

Multiple Alleles l When three or more alleles of the same gene exist in a population l i. e. blood types (A, B, O)

Continuous Variation l l - The range of small differences of a single trait in a population. It is usually where several genes effect a single trait.