Mendel and Traits

Genetics is the study of heredity!

Gregor Mendel

• Grew up in small region of Austria that is now part of the Czech Republic

• Many remember him as an Austrian monk

Gregor Mendel

• What did he do?– Bred pea plants to

study inheritance• Why is his work

important?– He discovered the

basic principles of heredity

– Father of Genetics!

Mendel’s Pea Experiment:Why Peas?

1. Many varieties w/ examinable traits

2. Was able to have strict control over how the pea plants mated

3. Peas plants had many “either/ or” characteristics that could be examined

What is a Trait?

What is a trait?

- Specific characteristic such as seed color or pod color in a pea plant.

Trait Alleles

Seed Shape Round (R ___)

Wrinkled (rr)

Seed Color Yellow (Y ___)

Green (yy)

Seed Coat color

Gray (W ___) White (ww)

Pod Shape Smooth (S ___)

Wrinkled (ss)

Pod Color Green (G ___)

Yellow (gg)

Flower Position

Axial (A ___) Terminal (aa)

Plant Height Tall (T ___) Short (tt)

Seven Traits Examined by Mendel

7 Traits Examined by Mendel

Seed Shape

Seed Color

Seed CoatColor

PodShape

Pod Color

Flower Position

Plant Height

Genes vs. Alleles• Genes: Location of a specific trait

on a chromosome• Alleles: alternate forms of a gene

with a slight difference in base sequence (A vs. a)

Dominant vs. Recessive

• Dominant: – In a pair of alleles, when one allele is

stronger than the other– This allele is expressed- the one that you

can “see”

• Recessive: – Weaker allele in a pair of alleles– The allele that is hidden

• Example: The allele for tall pea plants (T) is dominant over short pea plants (t)

Genotype vs. Phenotype

• Genotype = genetic makeup of an individual (think “gene = genotype”)– Example: the genotype for a pure tall pea

plant would be TT

• Phenotype = the expression of the genotype or the physical characteristics that you can see (think “physical = phenotype”)– Example: If the genotype for height in a pea

plant is tt, then you will see a short pea plant.

Homozygous vs. Heterozygous

• Homozygous – when both alleles in a pair are the same– think “homo = same”– also considered to be “pure”– Example: A pure tall pea plant is

homozygous dominant• Genotype = TT

• Heterozygous – when the alleles in a pair are different from

each other (think “hetero = different”)– Example: Tall pea plant with genotype = Tt

Genetics Practice: Determining Genotypes and Phenotypes

Trait Alleles

Seed Shape Round (R ___) Wrinkled (rr)

Seed Color Yellow (Y ___) Green (yy)

Seed coat color Gray (W ___) White (ww)

Pod Shape Smooth (S ___) Wrinkled (ss)

Pod Color Green (G ___) Yellow (gg)

Flower Position Axial (A ___) Terminal (aa)

Plant Height Tall (T ___) Short (tt)

1. What is the genotype of a heterozygous axial plant? ______________

2. What is the genotype of a wrinkled, short pea plant? ______________

3. What is the genotype of a purebred green pod plant? ______________

4. What is the phenotype for a ss plant? __________________________

5. What is the phenotype for a Aa plant? __________________________