Background InfoGregor Mendel

– Austrian Monk (1822-1884) – Father of Genetics – Genetics – study of

heredity– Heredity – passing of

characteristics from parent to offspring.

Background InfoGregor Mendel

– Identified that all traits are controlled by a “factor”

– This “factor” is a gene– GENE – section of a

chromosome/DNA that codes for a trait.

– TRAIT– characteristic passed from parent to offspring

Genome

• ALL of an organism’s genetic material

Background InfoGregor Mendel• Studied Pea Plants to show

how traits are passed from one generation to the next

• He applied math to his observations

• Studied pea plants because they came in 2 distinct forms

Why did he choose the Pea Plant?

• 1. The Structure of the Pea Flower

• 2. The seven distinct traits (2 distinct forms)

• 3. Rapid reproduction (Most pea plants reproduce in 90 days)

Pea Plant Traits

(Each trait only

has 2 distinct forms)

Genes & Alleles•Genes – chemical factors that

determine traits (Flower color)

•Alleles – different forms of genes that code for traits (Purple flowers or White flowers)

Mendel found Dominant and Recessive Traits

• An Allele is a distinct form of a gene

• A dominant allele is the form that is visibly seen.

• A recessive allele is the form that is there but not seen (unless there are 2 recessive alleles together).

Symbols•Dominant

Alleles–Capital Letters

•Recessive Alleles–Lower Case Letters

Genotypes

•Genotype–Genetic makeup represented by symbols

–AA, Aa, aa, TT, Bb, dd

Phenotypes

•Phenotype–Physical appearance expressed in words

–Brown hair, Green eyes, Freckles

Heterozygous

•Heterozygous (different)–Gene pairs that carry one dominant and one recessive allele

–Aa, Bb, Cc, Dd

Homozygous

•Homozygous (same)–Gene pairs that carry 2 dominant OR 2 recessive alleles

–AA, aa, BB, bb

Probability

•Determining the likelihood of an event to occur

•Can be shown in 3 ways–Fraction 1/2–Percent 50%–Ratio 1:2

Hybrids & Purebreds

•Hybrids receive different alleles from each parent (Hh, Bb, Zz)

•Purebreds receive the same alleles from each parent (HH, bb, ZZ)

Laws of Genetics• Law of Dominance: Dominant traits

will always show over recessive traits

• Law of Segregation: Alleles separate during meiosis

• Law of Independent Assortment: gene pairs separate randomly and independently of each other

Mendel’s Crosses• He started with 2 groups of purebred

plants, called the P1 generation.1. He crossed the purebreds by hand.

2. The P1’s offspring was called the F1 generation. The F1s then self-fertilized.

3. The F1’s offspring was known as the F2 generation.

Monohybrid CrossesA genetic cross that looks at 1 trait

• Cross a homozygous tongue roller with a non-tongue roller

• Genotype of parents– TT x tt

• Phenotypes of parents– Tongue roller, non-

tongue roller

• Possible Outcomes– Genotypic ratio

• 100%Tt

– Phenotypic ratio• 4 Tongue rollers:0 non-tongue

rollers

T T

t

tTtTt

TtTt

Monohybrid Crosses• Cross 2 Heterozygous

tongue rollers• Genotype of parents

– Tt x Tt

• Phenotypes of parents– Tongue roller, Tongue

roller

• Possible Outcomes– Genotypic ratio

• 1TT:2Tt:1tt

– Phenotypic ratio • 3 tongue rollers: 1 non-

tongue roller

T t

T

t

Tt tt

TtTT

Monohybrid Crosses• Cross a heterozygous

Tongue roller with a Non-Tongue roller

• Genotype of parents– Tt x tt

• Phenotypes of parents– Tongue roller, non-tongue

roller

• Possible Outcomes– Genotypic ratio

• 2Tt:2tt

– Phenotypic ratio • 2 tongue rollers:2 non-tongue

rollers

T t

t

t

Tt tt

ttTt

Dihybrid Crosses• A genetic cross that looks at 2 traits• Cross 2 heterozygous green, round

peas GgRr x GgRr• Genotypic Ratio

– 1:2:1:2:4:2:1:2:1• Phenotypic Ratio

– 9:3:3:1

G= green R= Roundg = yellow r = wrinkled

Dihybrid CrossesGR Gr gR gr

GR

Gr

gR

gr

Gg Rr

Gg RRGG RrGGRR

GG rrGG Rr

Gg Rr

Gg Rr

Gg rr

Gg RR

gg rrGg rrGg Rr

gg Rrgg RR

gg Rr