GENETICS

Section 11-1: The Work of Gregor Mendel

A. Gregor Mendel• 1. Born 1822 in Czech Republic• 2. Austrian monk• 3. Worked in the garden at the

monastery • 4. Experimented with the plants in

the garden: PEAS!• 5. Set foundation for Genetics

B. Flower reproduction (see Ch 24)

• 1. Fertilization within same plant– a. “self-pollination”

• Stamen ( male)– a. Anther: where meiosis makes pollen – b. Filament: stalk

• Carpel ( female)– a. Stigma: sticky, receptive part– b. Style: stalk– c. Ovary: where meiosis makes egg

C. Mendel’s Experiment• 1. Mendel manually cross pollinated the pea

plants in his garden• 2. He used “true-breeding” parents

– a. This meant that those plants always produced offspring that looked identical to the parents

• 3. He would cross one type of pea with another

• 4. He called the offspring hybrids• 5. He used seven traits in his experiments.

6. Generation Notation• a. P gen: Mendel manually fertilized one pea plant with

another to produce…• b. F1 gen: the 1st filial generation

– i. He let these offspring self-pollinate to produce…• c. F2 gen: the 2nd filial generation

• d. FYI…• For animals: you can think of these as:

– i. P your mom & dad, F1 you, F2 your kids someday– ii. In genetic experiments, F2 does not have to be “selfed” but

it often is. This should be specified

Mendel’s 7 Pea Traits• S

eed Shape

• Flower Position

• Seed Coat

• Color

• Seed Color

• Pod Color

• Plant Height

• Pod

• Shape

• Round

• Wrinkled

• Round

• Yellow

• Green

• Gray

• White

• Smooth

• Constricted

• Green

• Yellow

• Axial

• Terminal

• Tall

• Short

• Yellow • Gray • Smooth • Green • Axial • Tall

D. Results of Mendel’s Experiment

• 1. When Mendel crossed one type by the other for each trait – a. (eg. Green x yellow)

• 2. Only one of the traits showed up in the offspring.– a. Mendel called this trait DOMINANT.

• 3. Was the other variety of the trait gone forever?

• a. The other trait from the P generation showed up again in the F2 generation.

• b. Mendel called this trait RECESSIVE.• 4. Mendel called this the Principal of

Dominance: some alleles are dominant & some are recessive

E. ALLELES• 1. These traits were passed through generations– a. Also called “Genes” today– b. Factors had two forms:– c. “Alleles” = different forms of the

same gene• i. EX: height gene has tall & short

alleles

• 2. Capital letters = DOMINANT alleles

• 3. lowercase letters = recessive alleles

4. Simplest scenario…

–a. For each trait an individual has two alleles: one from each parent

–b. In turn, each individual can only pass one or the other of its alleles to its offspring.

• 5. Mendel called this separation of alleles SEGREGATION.

• 1. Phenotypes – a. actual appearance – b. think PHoto- PHeno

• 2. The way the trait shows itself• 3. If T is the allele for tallness and t is the allele

for a dwarf plant:– a. TT- tall plant – b. Tt- tall plant– c. tt- dwarf plant

F. Genetic Expression

4. Genotypes

• a. The actual genes (DNA) you have for a trait– a. TT- homozygous dominant– b. Tt- heterozygous– c. tt- homozygous recessive

• b. The letters represent actual genes inherited (one from each parent)

Mendel + Meiosis

Probability & GeneticsSection 11-2 Probability and Punnett Squares

A. ProbabilityA. What is probability? The likelihood a particular

event will occur• 1. Coin flipping

– a. Chances of heads? – b. Chances of tails?– c. Two coins– d. Chances of two heads? Two tails? Heads & tails?

• 2. Rule of Multiplication– a. Past events do not affect future probabilities

INDEPENDENT!

B. Punnett Squares

• 1. Used to show the possible outcomes for a trait according to the traits of the parents– a. What will happen?

• 2. Also show the probability of the outcome– b. How often it could

happen?

E e

3. Example: Ee x Ee

• a. Squares represent possible offspring

• b. Each offspring gets one gene from “dad” (from the top)

• c. and one gene from “Mom” (from the side)

• d. What % of the offspring will have free earlobes?

• e. What % will have attached ears?• f. What % will be heterozygous for

the trait?

EE

Ee

Ee ee

E

e

E

eDad

Mom

C. Fast Patterns to Know

Monohybrid Cross Genotype Ratio

(TT : Tt : tt)

Phenotype Ratio

(tall : short)

TT x tt

Tt x TT

TT x TT

tt x tt

Tt x Tt

tT x tT

Tt x tt

0:1:0

1:1:0

1:0:0

0:0:1

1:2:1

1:2:1

0:1:1

1:0

1:0

1:0

0:1

3:1

3:1

1:1