Genetics Notes

What is heredity?

A. Traits passing from offspring to parents

B. Traits passing from parents to offspring

C. Plants that are cross-pollinatedD. The ratio of dominant to recessive

traits

Heredity is

“C” - The passing of traits from parent to offspring

Who was Gregor Mendel?

Austrian Monk Conducted his research in a

monastery garden Worked with pea plants Discovered the principles of heredity

Self-pollinating Peas

Self-pollinating – when a plant fertilizes itself Results in a true-bred plant All the offspring of a true-bred plant will have

the same trait as the parent

Parent

Offspring

Cross-pollinating Peas

When one plant fertilizes a different plant

Pollen from one plant lands on the pistil and fertilizes the ovule (egg) of a different flower on a different plant

• Wind• Bees & other insects

First Generation Plants

First Generation Plants Self -Pollinated

X

F2 Second Generation

The white flowers reappeared! How did this happen?

Alleles: *different forms of a gene *exist in pairs (one from mom & one from dad)

Dominant allele– the prevailing (stronger) traitCapital Letter

Recessive allele– the (weak) hidden traitLower case letter

Genotype – the combination of alleles you have for a specific trait

• Ex: RR or Rr or rr

Phenotype – the physical feature you show or see

• Ex: Red flower petals, white flower petals

Example:

Gene: Flower Petal Color Alleles:

• Red (R)• White (r)

RR = homozygous dominantrr = homozygous recessiveRr = heterozygous

Homo – the same Hetero - different

Complete Dominance Rr = Red• dominant trait shows

Co Dominance RW = Red & White• Both traits show

Incomplete Dominance Rr = Pink• Traits are blended (mixed)

First Generation Plants Self -Pollinated

X

F2 Second Generation

The white flowers reappeared! HOW?

The parents were heterozygous (Rr).

RrRr

RRRr

Rr rr

Mendel’s Discoveries:

Each trait has two sets of instructions (alleles), one from each parent

Discovered dominant and recessive traits.

Intro. to Punnett Squares

A chart used to show all the ways genes from two parents can combine and be passed to offspring.