Download Mendel and Punnett Square notes

Mendel and Punnett Square notes
( text pages: 226-232)
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Genes come in pairs, one from each parent.
2 genes for eyebrow shape, blood type, etc.
These genes could be the same or different
1. Dominant gene:
- carries the dominant trait
- represented by uppercase letter
- because this gene is dominant, you only need one gene for the
trait to show.
Example: TT: 2 genes for tall
Homozygous: Same genetic trait
Tt: 1 gene for tall 1 gene for short. ( tall is dominant, short is recessive)
Heterozygous: 2 different genetic traits
2. Recessive gene
- carries the recessive trait
- represented by lower case letter
- 2 recessive genes are needed for the recessive trait to show
Example: tt: 2 recessive genes for short, plant is short.
Punnett Squares are used to predict the possible offspring for a cross between 2
parents.
Example: tall pea plant ( TT) x short pea plant ( tt):
T
T
Tt
Tt
Tt
Tt
Genotype: The genetic combination one from each parent. For the example all are
Tt .
Phenotype: what the offspring LOOKS like! The dominant gene always wins!
The example above all LOOK TALL.
Mendel took the offspring from the 1st cross and bred them:
Tt xTt
Results:
T
T
t
t
TT
Tt
Tt
tt
Ratio is 4:1 only 1
chance that the offspring
will show the recessive trait. 3 of the 4 will show the dominant trait.