Where are we going with this? The information on this page should increase understanding related to this standard: Identify patterns of inheritance to predict genotype/phenotype and solve punnett square problems.
Law of Independent Assortment
(Onward and upward?)
In order to have an axial plant, there must be at least one dominant "A" gene (AA or Aa). To have green seeds, requires that both of the genes be recessive (yy).
Can that happen?
REMINDER: Each parent will contribute one allele for each gene.
Yes; it is possible because you could inherit an “A” from either parent resulting in the genotype “AA” (axial).
You could also inherit a “y” from both parents resulting in the genotype “yy” (green).
This is possible because these genes are inherited separately from each other (Law of Independent Assortment).
We can visualize that with two punnett squares. Because the genes assort independently, you can do two independent Punnett squares to find out if this is possible.
What if you wanted to examine two traits at the same time using a single Punnett square? Is that possible?
Dihybrid Cross Punnett Squares
It is possible to set up two or more traits in one Punnett square. There's a process…
Recall that to look at one trait, the genotype of each parent is written, one at the top horizontally and one at the side vertically. (See above examples.)
When looking at more than one trait, the genotype will take on a form like…
Now, the same process is used… but with an added level of complexity.
To set up the square, write out the genotype for both, one at the top and one along the side.
In the above illustration, we have two homozygous parents:
Number the genes 1 to 4…
1 2 3 4
A a Y y
Going along the top, you will put in the genes in this order:
1 and 3
1 and 4
2 and 3
2 and 4
Do the same thing down the side to get what is shown in the image above.
Then, you fill in each box much like with a one trait Punnett square. Take the genes from the top and side and order them into the boxes. You would end up with this:
Law of Independent Assortment Recap
The Law of Segregation states that alleles separate independently during gamete formation.
Law of Independent Assortment states that genes separate independently during gamete formation.
Not all patterns of inheritance follow Mendelian Laws of dominance. There are other other systems by which traits can be passed from the parents to the offspring.
The most common example of this if crossing a red flower with a white flower and all offspring have pink flowers.
Though the homozygous parents are red and white, the heterozygous offspring are neither. They are a blend of the two.