Genetics

• Living things inherit traits in patterns.

Traits

• Some are inherited – Similar to those that your parents have• Hair Color• Eye Color

• Some are acquired– You develop them over your lifetime• Language• Reading and Writing• Riding a bike

The father of Genetics

• Gregor Mendel performed the first major experiments investigating heredity.– Austrian Monk– University trained in Math and Science– Experimented between 1856-1863– Investigated inheritance among pea plants in

monastery’s garden

Mendel’s Experiment• Mendel Observed seven different traits of pea

plants– Stem height, Seed Shape, Seed Color, Seed Coat

Color, Pod Shape, Pod Color, Flower Position

Mendel’s Experiment

• Using one trait at a time, Mendel crossed two plants of opposite forms for the same trait.

• Example– Trait – Plant Height

Mendel’s Observations.

• When crossing a tall pea plant with a dwarf pea plant produces 100% tall plants in the first generation.

• The dwarf trait disappeared.

Mendel’s Observations.

• When crossing the two plants from the first generation resulted in 75% tall plants and 25% dwarf plants

• The dwarf trait reappeared.

Mendel’s Conclusion

• Each plant must have two “factors” for each possible trait, one factor from each parent.

• Some forms of a trait can be masked• Traits able to be masked can only be seen if

both the plant’s factors are for that form of the trait.

• Mendel’s “factors” are known as genes and alleles

Two forms of every geneMendel found that we have two copies of each allele (one from mom, one from dad)

Dominate Alleles• Physically expressed

regardless of what other allele it is paired with

• Always expressed as a capital letter (T)

• Example: tallness is the dominate trait for pea plant height.

Recessive Alleles• Physically expressed only

when paired with another recessive allele

• Always expressed as a lower-case letter (t)

• Example: dwarfism is the recessive trait for pea plant height.

Alleles interact to produce traits

• Phenotype describes the physical– Characteristics that is displayed by your genes– Observable (eye color, hair color)

• Genotype describes the actual genes that you have on your DNA– Not always obvious

Codominance

• There are instances where the alleles are neither dominant nor recessive. As a result, both alleles are expressed in the offspring.

Punnett Square

• A Punnett Square is a way to show all the possible combinations of alleles that can result from a genetic cross.

• The following slides will show how you can figure the possible offspring when you cross two hybrid pea plants with round seeds (Rr)

• The dominate allele (R) is a round seed• The recessive allele (r) is a wrinkled seed

Punnett Square

• Start by drawing a box and dividing it into 4 squares.

Punnett Square• Write the male parent’s alleles along the top of the

square and the female parent’s along the left side.

RR

r

r

Punnett Square• Copy the female parents alleles into the boxes to

their right.

R R

r r

RR

r

r

Punnett Square• Copy the male parent’s alleles into the boxes

beneath them.

RR Rr

Rr rr

RR

r

r

Punnett Square• The completed Punnett square shows all the

possible allele combinations in the offspring.

RR Rr

Rr rr

RR

r

r

Probability• Dominate Trait R is a Round Seed• Recessive Trait r is a Wrinkled Seed• 75% chance of being Round• 25% chance of being Wrinkled

RR Rr

Rr rr