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Genetics Notes
What is heredity?
A.
B.
C.
D.
Traits passing from offspring to
parents
Traits passing from parents to
offspring
Plants that are cross-pollinated
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) trait


Capital Letter
Recessive allele– the (weak) hidden trait

Lower 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 dominant
rr = homozygous recessive
Rr = 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
Rr
RR
Rr
X
Rr
Rr
rr
The white flowers reappeared! HOW?
The parents were heterozygous (Rr).
F2 Second Generation
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.