Mendel and Traits
Jan 04, 2016
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? __________________________