Question

What is the difference between a phenotype and a genotype ratio?
I am doing an assignment on Blackboard Learn for school. They're asking me which chart shows the correct cross between a homozygous Tall plant and a short plant. I got that down.
Now they're asking for the ghenotype and phenotype ratio.
Somebody already tried to explain but it doesn't make any bloody sense.

Answer 1

@TheSmartOne

Answer 2

Start with a monohybrid cross Aa x Aa. Each parent can produce 2 gametes A and a, which can combine in 4 different ways AA, Aa, aA, aa The middle two are the same genotype. So you have 3 genotypes 1 x AA, 2 x Aa and 1 x aa, so your genotype ratio is 1:2:1. Three genotypes AA and 2x Aa both give the same phenotype, so you get 3 of one phenotype and only 1 aa phenotype, so the phenotype ratio is 3:1.

For a dihybrid cross you follow exactly the same steps, except that this time you are considering 2 genes at the same time. AaBb x AaBb is the cross, and each parent can produce 4 gametes AB, Ab, aB and ab. The only way to look at the outcome of this cross is to draw a Punnett square with each of the 4 gametes in the rows and columns and the combinations in each box of the square. With 4 x 4 you will get 16 outcomes, some will be the same.

If we look at the first row, so AB x AB/Ab/aB/ab, the genotypes will be AABB, AABb, AaBB and AaBb. There are 4 different genotypes in this row, but all will have the same phenotype as all have at least 1 A and 1 B. You should draw out the whole table to understand this properly.

If you do it properly you will get a genotype ratio of 1:2:1:2:4:2:1:2:1. The first 1, is AABB, the 4 in the middle is AaBb and the last 1 is aabb - you should be able to find all of the others.

Then count up all of the different phenotypes. You should find 9, that have at least 1 A and 1B (these show the dominant phenotype for both A and B), 3 that have at least 1 A and bb (these are dominant for A but recessive for B), 3 that have aa and at least 1 B (recessive for A and dominant for B) and 1 aabb which is recessive for both characters, so your phenotype ratio for a dihybrid cross is 9:3:3:1.
HOPE THIS HELPS (:

Answer 3

Site your sources @timbo5lice @~

https://answers.yahoo.com/question/index?qid=20130918000235AAZMwXp

Answer 4

I saw that when I had originally looked it up.
It doesn't make any bloody sense though.

And they're trying to teach 12-13 year old kids this?
I appreciate it, but is there any other way to explain it?

Answer 5

This video seems really helpful:
https://www.youtube.com/watch?v=6WUC4JEus84

Answer 6

i agree (: