Biology I - GENETICS 1-12 Novak

Gregor Mendel 1822-1884

MENDEL’S PRINCIPLES

I. ALLELES Any organism has two units of heredity (genes) for each trait in every body cell

II. SEGREGATION The two units (genes) for a trait are separated in the cell; one gene is found on a chromosome while the other is located in the same place on its partner (homologous) chromosome

III. DOMINANCE A. When two genes of a trait are different in the cells of the organism, the gene that shows up is the dominant while the gene that remains hidden is the recessive B. Combinations of the two genes (genotypes) 1. Homozygous (pure) dominant - both genes are dominant 2. Homozygous (pure) recessive - both genes are recessive 3. Heterozygous (hybrid) - one gene is dominant & the other is recessive

IV. RECOMBINATION - (INDEPENDENT ASSORTMENT) In each new generation there is a complete new rearrangement of the units of heredity (genes)

Following the Generations Cross 2 Pure Plants TT x tt Results in all Hybrids Tt Cross 2 Hybrids get 3 Tall & 1 Short TT, Tt, tt

Generation “Gap” Parental P1 Generation = the parental generation in a breeding experiment. F1 generation = the first-generation offspring in a breeding experiment. (1st filial generation) From breeding individuals from the P1 generation F2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation) From breeding individuals from the F1 generation

Mendel’s Experimental Results

Thomas Hunt Morgan 1866-1945

Incomplete Dominance (blending inheritance)

INCOMPLETE DOMINANCE A condition in which both alleles for a characteristic are partially expressed

Incomplete Dominance F1 hybrids have an appearance somewhat in between or a blend of the phenotypes of the two parental varieties. Example: snapdragons (flower) red (RR) x white (WW) R = red flower W = white flower R W

Incomplete Dominance R RW produces the F1 generation All RW = pink (heterozygous pink) produces the F1 generation W RW W

Incomplete Dominance

CODOMINANCE A condition in which both alleles for a characteristic are fully expressed

Codominant white and pink

Codominant white and pink

Homozygous Red

Hereford Red

Homozygous white

Roan hybrid

Roan hybrid

Codominant cross

DIHYBRID INHERITANCE

These are the genotypes of the two plants. Pea Plants Seed Color Height Tall = TT, Tt Short = tt Yellow = YY, Yy Green = yy Let’s cross a homozygous tall (TT), homozygous yellow seed (YY) plant with a short (tt), green seed (yy) plant. TTYY x ttyy These are the genotypes of the two plants.

Independent Assortment Mendels’ principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes (eggs & sperm in animals, eggs and pollen in plants). First T TTYY with first Y T Y Gamete 1 = sperm, egg, pollen . . .

Independent Assortment Mendels’ principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes (eggs & sperm in animals, eggs and pollen in plants). First T TTYY with second Y TY T Y Gamete 1 Gamete 2

Independent Assortment Mendels’ principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes (eggs & sperm in animals, eggs and pollen in plants). Second T TTYY with first Y TY TY T Y Gamete 1 Gamete 2 Gamete 3

Independent Assortment Mendels’ principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes (eggs & sperm in animals, eggs and pollen in plants). Second T TTYY with second Y TY TY TY T Y Gamete 1 Gamete 2 Gamete 3 Gamete 4

Dihybrid Punnett Square - F1 P1 = TTYY TY ty Will be F1 Generation P2 = ttyy

Dihybrid Punnett Square - F1 TY ty TTYy

Dihybrid Punnett Square - F1 TY ty TtYy TTYY TtYY

Dihybrid Punnett Square - F1 TY ty TtYy

Dihybrid Punnett Square - F1 TY ty TtYy Genotype ratio: TtYy - 16/16 Phenotype ratio: Tall, Yellow - 16/16

Dihybrid Punnett Square – F2 We need to pair up the genes which can be given to each gamete (egg and pollen). Let’s cross two of the plants from the F1 generation We need to pair up the genes TY ty TtYy . x T Y T y t Y t y

Dihybrid Punnett Square F2 TY Ty tY ty Both the plants can give the same gene combinations to their gametes, so the pairs along the top and down the side are the same.

Dihybrid Punnett Square – F2 When you pair up the gametes from the two plants, always put like letters together and within the like letters, put the CAPITAL letter in front of the lowercase letter.

Dihybrid Punnett Square F2 TY Ty tY ty TTYY TTYy TtYY TtYy ???? Your Turn!!

Dihybrid Punnett Square F2 TY Ty tY ty TTYY TTYy TtYY TtYy TTyy Ttyy ttYY ttYy ttyy F2 generation

Dihybrid Punnett Square F2 Genotype and phenotype ratios? TY Ty tY ty TTYY TTYy TtYY TtYy TTyy Ttyy ttYY ttYy ttyy

F2 Genotype Ratio TTYY - 1 TTYy - 2 TtYY - 2 TtYy - 4 TTyy - 1

F2 Phenotype Ratio TTYY - 1 TTYy - 2 TtYY - 2 TtYy - 4 Tall, Yellow - 9 Tall, Green - 3 Short, Yellow - 3 Short, Green - 1

Another Mendelian Dihybrid Problem

Dihybrid F2 Results

Dihybrid F2 Results

Sex-Linked Inheritance

Color Blindness

TYPES OF COLOR BLINDNESS normal - trichromatic color vision protanopia red-green blindness (no red cones) deutanopia red-green blindness (no green cones) tritanopia blue-yellow blindness (no blue cones) typical achromatopsia (no cones; rod monochromat) protanomaly (anomalous red cones) deutanomaly (anomalous green cones) tritanomaly (anomalous blue cones) atypical achromatopsia (low cones; cone monochromat)

Red Green Color Blindness Male1.01% Female0.02%

Sex-linked Traits Traits (genes) located on the sex chromosomes Sex chromosomes are X and Y XX genotype for females XY genotype for males Many sex-linked traits carried on X chromosome

Hemophilia

Female Carriers

The effects of hemophilia

Human Blood Coagulation Cascade

The End