biology i - genetics 1-12 novak gregor mendel 1822-1884

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 dominant2. Homozygous (pure) recessive - both genes are recessive3. 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 GenerationsFollowing the Generations

Cross 2 Cross 2 Pure Pure

PlantsPlantsTT x ttTT x tt

Results Results in all in all

HybridsHybridsTtTt

Cross 2 Cross 2 HybridsHybrids

getget3 Tall & 1 3 Tall & 1

ShortShortTT, Tt, ttTT, Tt, tt

Generation “Gap”Generation “Gap”• Parental PParental P11 Generation Generation = the parental generation in a breeding experiment= the parental generation in a breeding experiment..• FF11 generation generation = the first-generation offspring in a breeding experiment. = the first-generation offspring in a breeding experiment.

(1st filial generation)(1st filial generation)– From breeding individuals from the PFrom breeding individuals from the P11 generation generation

• FF22 generation generation = the second-generation offspring in a breeding experiment. = the second-generation offspring in a breeding experiment.

(2nd filial generation)(2nd filial generation)– From breeding individuals from the FFrom breeding individuals from the F11 generation generation

Mendel’s Experimental Mendel’s Experimental ResultsResults

Thomas Hunt Morgan

1866-1945

Incomplete Dominance Incomplete Dominance (blending inheritance)(blending inheritance)

• INCOMPLETE DOMINANCE

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

Incomplete DominanceIncomplete Dominance• F1 hybrids F1 hybrids have an appearance somewhat in betweenin between or a blend of the

phenotypes phenotypes of the two parental varieties.• Example:Example: snapdragons (flower)snapdragons (flower)• red (RR) x white (WW)

• R = red flowerR = red flower• W = white flower

W

W

R R

Incomplete DominanceIncomplete Dominance

RWRW

RWRW

RWRW

RWRW

RR RR

All RW =All RW = pink pink(heterozygous pink)(heterozygous pink)

produces theproduces theFF11 generation generation

W

W

Incomplete DominanceIncomplete 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

Sex-Linked Inheritance

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)

TYPES OF COLOR BLINDNESS

Red Green Color BlindnessMale1.01%Female0.02%

Sex-linked TraitsSex-linked Traits• Traits (genes) located on the Traits (genes) located on the sex chromosomessex chromosomes• Sex chromosomes are Sex chromosomes are X and YX and Y• XXXX genotype for females genotype for females• XYXY genotype for males genotype for males• Many Many sex-linked traitssex-linked traits carried on carried on XX chromosome chromosome

Hemophilia

Female CarriersFemale Carriers

The effects of hemophilia

Human BloodCoagulationCascade

DIHYBRID INHERITANCE

Pea Plants

Tall = TT, TtShort = tt

Height Seed Color

Yellow = YY, YyGreen = 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).

TTYY

TY

First T with first 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).

TTYY

TY TY

First T with second 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).

TTYY

TY TY TY

Second T with first 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).

TTYY

TY TY TY YT

Second T with second Y

Gamete 1 Gamete 2 Gamete 3 Gamete 4

Dihybrid Punnett Square - F1

TY TY TY TY

ty

ty

ty

ty

P1 = TTYY

P2 = ttyy Will be F1 Generation

Dihybrid Punnett Square - F1

TY TY TY TY

ty TTYy

ty TTYy

ty TTYy

ty TTYy

Dihybrid Punnett Square - F1

TY TY TY TY

ty TtYy TtYy TtYy TtYy

ty TTYY TtYY TtYY TTYY

ty TTYY TTYY TTYY TTYY

ty TTYY TTYY TTYY TTYY

Dihybrid Punnett Square - F1

TY TY TY TY

ty TtYy TtYy TtYy TtYy

ty TtYy TtYy TtYy TtYy

ty TtYy TtYy TtYy TtYy

ty TtYy TtYy TtYy TtYy

Dihybrid Punnett Square - F1

TY TY TY TY

ty TtYy TtYy TtYy TtYy

ty TtYy TtYy TtYy TtYy

ty TtYy TtYy TtYy TtYy

ty TtYy TtYy TtYy TtYy

Genotype ratio:TtYy - 16/16

Phenotype ratio:Tall, Yellow - 16/16

Dihybrid Punnett Square – F2We 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

TY TY TY TY

ty TtYy TtYy TtYy TtYy

ty TtYy TtYy TtYy TtYy

ty TtYy TtYy TtYy TtYy

ty TtYy TtYy TtYy TtYy

x

.

TY Ty t Y yt

We need to pair up the genes

Dihybrid Punnett Square F2

TY Ty tY ty

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

TY TTYY TTYy TtYY TtYy

Ty ???? ???? ???? ????

tY ???? ???? ???? ????

ty ???? ???? ???? ????

Your Turn!!

Dihybrid Punnett Square F2

TY Ty tY ty

TY TTYY TTYy TtYY TtYy

Ty TTYy TTyy TtYy Ttyy

tY TtYY TtYy ttYY ttYy

ty TtYy Ttyy ttYy ttyy

F2 generation

Dihybrid Punnett Square F2

TY Ty tY ty

TY TTYY TTYy TtYY TtYy

Ty TTYy TTyy TtYy Ttyy

tY TtYY TtYy ttYY ttYy

ty TtYy Ttyy ttYy ttyy

Genotype and phenotype ratios?

F2 Genotype RatioTTYY - 1TTYy - 2TtYY - 2TtYy - 4TTyy - 1Ttyy - 2ttYY - 1ttYy - 2ttyy - 1

F2 Phenotype RatioTTYY - 1TTYy - 2TtYY - 2TtYy - 4TTyy - 1Ttyy - 2ttYY - 1ttYy - 2ttyy - 1

Tall, Yellow - 9

Tall, Green - 3

Short, Yellow - 3

Short, Green - 1

Another Mendelian Dihybrid Problem

Dihybrid F2 Results

Dihybrid F2 Results

•The End