Question

You perform a dihybrid cross of plants. The first trait is flower color. “A” is the dominant allele and causes red petals and “a” is the recessive allele and causes white petals. Stem length is the second trait. “L” is the dominant allele and causes a long stem and “l” is the recessive allele and causes short stems. You cross a Red Long plant that is heterozygous for both traits with a Red Short plant that is heterozygous for color.

1. How many different types of gametes can the red long plant make?

2. How many different types of gametes can the red short plant make?

Assume that 80 plants are the offspring of this cross. Given that number, how many of the 80 offspring will fall into each of the following categories?

3. Red Long:

4. Red Short:

5. White Long:

6. White Short:

Answer 1

Given that,

“A” is the dominant allele and causes red petals and “a” is the recessive allele and causes white petals.

“L” is the dominant allele and causes a long stem and “l” is the recessive allele and causes short stems.

The cross is between Red Long plant that is heterozygous for both traits (AaLl ) and a Red Short plant that is heterozygous for color (Aall).

Therefore the genotype of the parents will be

AaLl X Aall

Gametes from AaLl will be - AL, Al, aL, al

Gametes from Aall will be - Al, Al, al, al

The punnet square is given below

From the punnet square, the number of different plants out of 16 is

• Red long plants = 6
• Red short plants=6
• White long plants= 2
• White short plants=2

If the plant produces 80 offsprings, we can calculate the number of different plants from the above details. Ie

• Red long plants out of 80 offspings = (6/16) x 80= 30
• Red short plants out of 80 offspings = (6/16) x 80= 30
• White long plants out of 80 offspings = (2/16) x 80 = 10
• White short plants out of 80 offspings = (2/16) x 80 = 10

Finally,

1. Number of different types of gametes produced by red long plant (AaLl) will be - Four (AL, Al, aL, al)

2. Number of different types of gametes produced by red short plant (Aall) will be - Two (Al and al)

Out of 80 offsprings, number of

• Red long plants will be 30
• Red short plants will be 30
• White long plants will be 10
• White short plants will be 10