Question???

• If two blue eyed people have kids, what color eyes will their kids have?

• If two brown eyed people have kids, what color eyes will their kids have?

• Have color sticks!

Genetics: Episode IA Monk, His Peas, and Genes

Ag BiologySutherlin AST

Genetics

• What is genetics?– Branch of biology studying heredity

• What is heredity?– Passing of traits from parent to offspring

• What are traits?– Physical characteristics

Genetics

• Gregor Mendel– A monk, 1800’s Austria– First to study and determine

factors of heredity– Used carefully controlled

experiments: only changed one factor at a time

Genetics

• Why peas?– Produce sexually– Male and female

parts on same flower• Male parts are

called?• Female parts are

called?

Genetics

• Pollination – male sex cells (pollen) lands on female parts (pistil)

• Fertilization – DNA from pollen combines with DNA from ovum (egg)– Becomes seed

Genetics

• Self-pollination: male and female sex cells come from same plant

• Cross-pollination: sex cells come from two different plants– Create hybrid

Genetics

• What did Mendel do?– Studied TALL traits and SHORT traits in plants

(parents = P1)– Cross-pollinated these plants to get hybrids

– ALL of the offspring (F1) were TALL

Genetics

• What did Mendel do next?– Took the offspring (F1), then crossed them

together

– This time, not all offspring the same.

Genetics

• What did Mendel do next?– ¾ of plants were tall– ¼ were short plants– This is called a 3:1 ratio

Genetics

So what does this mean?• Unit Factors– Mendel concluded two factors control each trait– We know these are genes• One factor from the mother• One from the father

Genetics

• Unit Factors– For each gene, there are

alleles• Different forms of each

gene• Example: there is a gene

for height (T)

It could be the Tall allele – T It could be the Short allele - t

Genetics

• Unit Factors– Since we have two copies of each gene, three

combinations• Two Tall (TT) alleles• Two Short (tt) alleles• One Tall allele and one

short allele (Tt)

But how is this possible?

Genetics

What else does this mean?• Rule of Dominance– Only one allele is observable– Dominant alleles: observable trait– Recessive alleles: unobservable trait

– So which is dominant for height in pea plants?

Genetics

• So what does each look like?

– TT:

– tt:

– Tt:

Genetics

• What about cows?– If you cross purebred black angus cattle with red

angus cattle, you get black cattle

– What does this mean?

Question:

1. You are growing peas. Use the chart of dominant and recessive genes.

You are crossing axial (AA) and terminal (aa) bud plants. What would the F1 generation be?

Would terminal or axial be more beneficial for the plant?

Mendel’s 7 Traits of Pea Plants

Genetics

• Two organisms can look the same, but carrying different genes

• Phenotype: how an organism looks (think physical)– Tall? Short?

• Genotype: the genes an organism has– Tall: could be Tt– Tall: could be TT

Genetics

• Homozygous – both alleles are the same– TT, tt

• Heterozygous – alleles are different– Tt

All of this, by a monk, in the 1800s!

Genetics

• Dihybrid cross– Looking at just one trait (height) is monohybrid

(one)– But what if we track more than one trait?

Genetics

• Mendel’s Dihybrid Cross– Round peas (R=round, r=wrinkled)– Seed color (Y=yellow, y=green)

Parents (P1)Round Yellow X Wrinkled Green

Genetics

• Mendel’s Dihybrid Cross Parents (P1)

Round Yellow X Wrinkled GreenRRYY rryy

Result? Offspring (F1) ALL Round YellowsRrYy

Genetics

• Mendel’s Dihybrid CrossF1 Cross

X

So now what do you get?

Genetics

• Mendel’s Dihybrid Cross– The point?– Law of Independent Assortment: genes for

different traits are inherited independently of one another (green seeds do not have to be wrinkled!)

Genetics

• Punnett Squares– Tool for projecting Phenotypes and Genotypes of

offspring– Developed by Reginald Punnett (England)

Genetics

• Monohybrid Punnett Square

Genetics

• Dihybrid Punnett Square