Question

bio 223 monohybrid 10 points your name: date: 9/11/23
lab 1: in - class monohybrid cross exercise

1. in garden peas, smooth seed shape(r) is dominant over wrinkled seeds (r). what are the genotypic and phenotypic ratios of a cross between a homozygous dominant male and a recessive female?
2. in peas, yellow color (y) is expressed in the presence of the dominant allele and green color (y) is recessive. what are the genotypic and phenotypic ratios of a cross - pollination between a heterozygous female and a heterozygous male?
3. lets say that in seals, the gene for the length of the whiskers has two alleles. the dominant allele (w) codes for long whiskers and the recessive allele (w) codes for short whiskers. a) what percentage of offspring would be expected to have short whiskers from the cross of two long - whiskered seals, one that is homozygous dominant and one that is heterozygous?

b) if one parent seal is pure long - whiskered and the other is short - whiskered, what percent of offspring would have long whiskers?

1. in purple people eaters, one - horn is dominant (h) and no horns is recessive (h). draw a punnett square showing the cross of a purple people eater that is heterozygous for horns with a purple people eater that does not have horns. write out the genotypic and phenotypic ratios of the possible offspring.

Explanation:

Step1: Analyze the cross in question 1

The cross is between a homozygous dominant (RR) male and a recessive (rr) female. The male can only produce R gametes and the female can only produce r gametes.
All offspring will have the genotype Rr (100% Rr). The phenotypic ratio is 100% smooth - seeded (since R is dominant). So the genotypic ratio is 1:0 (Rr:rr) and phenotypic ratio is 1:0 (smooth:wrinkled).

Step2: Analyze the cross in question 2

The cross is between a heterozygous (Yy) male and a heterozygous (Yy) female. The possible gametes from each parent are Y and y. Using a Punnett - square, we have:

	Y	y
y	Yy	yy

The genotypic ratio is 1:2:1 (YY:Yy:yy) and the phenotypic ratio is 3:1 (yellow:green) since YY and Yy are yellow and yy is green.

Step3: Analyze question 3a

The cross is between a homozygous dominant (WW) and a heterozygous (Ww) long - whiskered seal. The homozygous dominant can only produce W gametes and the heterozygous can produce W and w gametes.
All offspring genotypes are WW or Ww. None of the offspring will have short whiskers (ww). So the percentage of offspring with short whiskers is 0%.

Step4: Analyze question 3b

The cross is between a pure long - whiskered (WW) and a short - whiskered (ww) seal. The pure long - whiskered can only produce W gametes and the short - whiskered can only produce w gametes.
All offspring will have the genotype Ww and will have long whiskers. So 100% of the offspring will have long whiskers.

Step5: Analyze question 4

The cross is between a heterozygous (Hh) and a non - horned (hh) purple people eater. The heterozygous can produce H and h gametes and the non - horned can produce only h gametes.
The Punnett - square is:

	H	h

The genotypic ratio is 1:1 (Hh:hh) and the phenotypic ratio is 1:1 (one - horned:no horns).

Answer:

1. Genotypic ratio: 1:0 (Rr:rr), Phenotypic ratio: 1:0 (smooth:wrinkled)
2. Genotypic ratio: 1:2:1 (YY:Yy:yy), Phenotypic ratio: 3:1 (yellow:green)

3a. 0%
3b. 100%

1. Genotypic ratio: 1:1 (Hh:hh), Phenotypic ratio: 1:1 (one - horned:no horns)