The probability of a chance or event is independent of any other chance or event. The probability of two or more events occurring together is equal to the product of their individual probabilities. Laws of Probability

Expressivity – the extent to which a phenotype shows in an individual in a population. E.g. how brown is hair color? Penetrance – the extent to which a phenotype is carried by members of a population Expressivity & Penetrance

Amniocentesis CVS - chorionic villus sampling Linkage maps/cytological maps Analysis and Diagnosis

Mendel and His Peas A Look Into Genetics

Gregor Mendel ’s Austrian (modern Czech) Monk Observed “traits” or “factors” in pea plants in his monastery garden Kept good records Never published... Gregor Mendel: Classical Genetics

Traits - logical, probability terms used by Mendel to describe his work. Allele - one of two (or more) expressions of a trait in a trait pair. Gene - section of DNA responsible for the translation of a protein (enzyme) Traits, factors, alleles, genes...

Round or wrinkled peas Sweet or starchy peas Green or yellow peas Inflated or wrinkled pods Green or gray pods Tall or short plants Terminal or axial flowers Traits of Peas….Mmm

Peas – True Breeding Round pea seed wrinkled pea seed Round pea seeds produce round plants wrinkled pea seeds produce wrinkled plants

Crossing Peas x Mendel crossed a purebred round with a purebred wrinkled pea, thinking that the offspring would be a blend of the two traits...

Crossing Peas x Instead he found that the first offspring generation was all round… This led him to assert that round was dominant to wrinkled.

Crossing Peas x When he allowed the first offspring generation to self- pollinate.. …the second offspring generation showed both traits.

Naming the generations x P1 Parental generation F1 First filial generation F2 Second filial generation

The Genes that Cause the Traits... x RR Rr rr RR Rr rr Rr R R rr R r Rr RRRr rrRr

Genotype - letters or symbols for the genes involved: RR, Rr, rr; TT, Tt, tt Phenotype - adjectives that describe the trait: round, wrinkled, tall, short Genotype and Phenotype

The genotype causes the phenotype… The phenotype is the expression of the genotype...

Homozygous (purebred) - both alleles in the allele pair are identical Heterozygous (“hybrid”) - the two alleles in the allele pair are different Purebreds and Hybrids

Another set of alleles...

Just as in the P1 cross of purebred dominant with purebred wrinkled… All the F1 individuals will show the dominant trait (and heterozygous genotype) P1 Cross: Homozygous Tall with Homozygous Short... TTttx T T tt Tt

x T t Tt TTTt ttTt Now the F1 can cross And produce the characteristic 3:1 ratio of phenotypes… (and 1:2:1 ratio of genotypes…) F1 Cross: Self-pollination of hybrid

Because the F1 (self-pollinations) crosses are ones between hybrids for one allele, they are often called monohybrid crosses. It is an excellent example of classical genetics. Monohybrid Cross

Monohybrid Crosses show the segregation of two alleles in the same allele pair.

Monohybrid cross shows the segregation of alleles of the same allele pair into different gametes... Dihybrid cross ? More Classical Genetics

Green - Yellow Pea

Green/yellow crosses

G/y Phenotypes/Genotypes

G/y Punnett Squares

Dihybrid Cross

P1 Cross

F1 Cross

RrYy Dihybrid Cross RYRy RY Ry rY ry rY RRYYRRYy RRyyRRYy RrYYRrYy RryyRrYy Rryy rrYy rryy RrYY RrYy rrYY rrYy

RrYy Dihybrid Cross

Phenotype Ratios RYRy RY Ry rY ry rY Round Yellow Round Green Wrinkled Yellow Wrinkled Green :3:3:1

Genetic Recombination RtTr This is a diploid cell right after mitosis. Note that there are 4 paired chromosomes Each chromosome has only one chromatid

RRtt TTrr S-phase chromosomes After S-phase (i.e. DNA synthesis)… There are still only 4 chromosomes… Each chromosome now has two chromatids.

Metaphase-1 OR RR ttTT rr TTtt RR Because the chromosomes synapse at random on the metaphase plate.. Two different combinations are possible with two pairs of chromosomes.

Anaphase-1

…and this means more varied recom- binations are possible. Metaphase-2

Anaphase-2

Gametes ALL POSSIBLE GAMETES 2 CHROMOSOMES EACH RT rT Rtrt Rt