| P
& P |
||
| Probability
and Punnett Squares |
| Ever
wonder why you have
a certain color of hair or eyes? Ever wonder why you may have dimples?
It's all in the genes and which parent you inherit the trait
from. When developing as a fetus, you inherit one allele from your mom
and one
from
your dad. These alleles can be either dominant or recessive. For
example,
if you inherited a allele that's dominant for brown eyes, you will have
brown eyes. Let's look at the genotype Bb and say B represents brown
eyes and b represents blue eyes. Here, brown eyes are dominant because
they're represented by a capital B and the eye color is a stronger
trait. Inherited traits from two parents can also be shown by
using a table called a Punnett square such as the one pictured below. |
| B |
B |
|
| b |
Bb |
Bb |
| b |
Bb |
Bb |
|
Punnett
Squares show one of the parent's genes or trait on the top row, and the
other parent's trait on the left column. From the one pictured above we
can see the one parent has brown eyes with a genotype of BB, and the
other has blue eyes with a genotype bb. The offspring of these parents
all have a genotype of Bb, which would mean their phenotype is
brown-eyed. The parents probability of having a child with brown
eyes is 100%, a 4:0 ratio. |
| R |
r |
|
| R |
RR |
Rr |
| r |
Rr |
rr |
| If the
Punnett
Square above displays both parents with a genotype of Rr, which means
both of
them have a phenotype of brown hair, what are the probable phenotypes
and genotypes of their children? Try to solve the mystery and check
with someone and discuss why you are correct. Remember, always write
the capital letter first! For an extra challenge, try the Punnett
Square picture below. |
| B |
b |
R |
R |
|
| B |
||||
| b |
||||
| R |
||||
| R |
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