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Genetics
The study of
heredity
Mendel
1860’s Austrian Monk
Worked with pea plants
Used his math background to
make new hypotheses about
inheritance.
Mendel’s Experiments
Example of Mendel’s work
Mendel hypothesized that each
trait is controlled by a “factor”
2 or more “factors” for each trait
•Dominant-more powerful,
always shows (R)
•Recessive-weaker, sometimes
shows (r)
Mendel knew that 2 parents
contribute to inheritance.
Therefore, each
organism must
have 2 factors for
each trait. These
factors later
became known as
genes.
Purebred (homozygous)
•both genes the same
•RR, rr
Hybrid (heterozygous)
•genes are different
•Rr
Mendel’s 3 Laws
1. Law of Segregation –
genes separate when
gametes form
2. Law of Dominance –
when 2 different alleles
in a gene pair are
present only one gene
is expressed
Law of Independent
Assortment – gene pairs
segregate into gametes
randomly and independent
of each other.
3.
Genotype – the actual genetic
makeup of the organism
Phenotype – the form of the trait
expressed
(letters)
(word)
Punnett Square
Used to predict the
outcome of a genetic
cross.
Dihybrid Cross: 2 factors
1. Assign letters
2. Set up cross
3. Create Punnett square
4. Determine genotypes
5. Determine phenotypes
Golden fur is dominant over silver
fur.
Long fur is dominant over short fur.
1. Cross a homozygous golden long
furred dog with a heterozygous
golden furred dog with short hair.
Golden fur is dominant over silver
fur.
Long fur is dominant over short fur.
2. Cross a homozygous silver
long furred dog with a
heterozygous golden long
furred dog.