Question

1. If a true-breeding white flowered plant is bred with a true-breeding purple flowered plant, what are the genotypes of the offspring?

A. heterozygous
B. homozygous dominant and heterozygous
C. heterozygous dominant
D. homozygous dominant and homozygous recessive
E. homozygous dominant, heterozygous, and homozygous recessive
2. Given what we know about Mendelian genetics, what is the genotype of pea plants with white flowers? White is a recessive trait while purple is a dominant trait.
A. heterozygous
B. w
C. homozygous recessive
D. hemizygous recessive
E. pw
3. Coat color for a breed of cattle is determined by two co-dominant alleles, one for white (W) and one for red (R). A heterozygote will be a mixed color, called roan. Crossing two roans produces an equal number of white or red offspring and twice as many roans. If a farmer wanted a herd of cattle that were all roans, what color should the two parents be?
A. Roan and roan.
B. Roan and white.
C. Roan and red.
D. White and red.
E. Red and red.

Answer 1

1. C. Heterozygous dominant

2. C. Homozygous recessive

3. D. White and Red

Step-by-step explanation:

1. True breeding means homozygous dominant.

• Use letters to show what you are working with:

• True breeding white flower is: WW and a true breeding purple flower is PP (capital letters show that the trait is dominant)

• WW crossed with PP = WP and WP offspring.
• Therefore WP- dominant and heterozygous

2. White is a recessive trait and thus for white flowers the genotype needs to be homozygous recessive.

• Purple is a dominant trait and thus any genotype where there is a purple allele the flowers will be purple - thus the genotype must be homozygous.
• The homozygosity must be for white, which is recessive trait therefore the genotype needs to be recessive.

3. Only the white and red will give a herd of all roans.

• Use letters again to define the genotypes
• Roan: WR, White: WW and Red:RR ( all the letters are capitals because these are dominant alleles)
• Do the individual crosses to show which cross will give a herd of only Roans (WR)
• WR crossed with WR yields: WW, WR, WR and RR
• WR crossed with WW yields: WW, WW,WR, WR
• WR crossed with RR yields: WR, WR, RR, RR
• WW crossed with RR yields: WR, WR, WR, WR (all roan). White and Red parents will give the roan phenotype
• RR crossed with RR yields: RR

Answer 2

1: A true-breeding white flower plant means that is homozygous (a pure genotype), the same can be said for a true-breedingm purple flower.

If you do the punnet square for the the plants you will see that all of their offspring will be heterozgous (an impure genotype).

Now pretend white is reccessive and purple is a dominant trait. You will see that all genotypes have a dominant allele inside. Thus, their offspring will be purple not white.

The correct answer will be:

C. hetrozygous dominant

2: The answer will once more be:

A. Heterozygous

3: The answer is:

D. White and red.

If you breed a roan cow and another roan cow, you will get a 50% of roan calves, 25% white calves, 25% red calves. If you breed a roan and white you will get 50% roan and 50% white calves. If you breed a roan and a red, you will get 50% red calves and 50% roan calves. If you breed a red cow and another red cow, you will get 100% red cows.

These statistics may or may not change depending if the parents are pure-breed (homozygous) or heterozygous.