Question

In Mendel's pea plants, the allele for purple flowers (P) is dominant to the allele for white flowers (p). You cross two pea plants that are heterozygous for the flower color trait and obtain 36 peas. When you plant these peas and grow them long enough to see their flowers, you find that 25 of them have purple flowers and 11 of them have white flowers. (a) For this cross, what are the expected values for each phenotype? (1 point) (b) What is the difference between the observed and expected number for each phenotype? (1 point) Based on previous observations of pedestrians on a city street, you can expect that one-quarter of the pedestrians you see will be carrying an umbrella. The results from a different observation lead you to expect that one-half of the pedestrians you see will be wearing a backpack. (a) If you later return to the street and observe 80 pedestrians, how many would you expect to be carrying an umbrella and wearing a backpack? Show your calculations. (1 point) (b) If you observe 40 pedestrians, how many would you expect to be carrying an umbrella or wearing a backpack? Show your calculations. (1 point) Certain genes (technically, the proteins encoded by those genes) are essential for embryonic development in C. elegans. For the lit-1 gene, the dominant allele allows normal development in both homozygous dominant (lit-1+/+) embryos and heterozygous embryos (lit-1/+). Embryos that are homozygous recessive (lit-1/lit-1) die early in embryogenesis. A heterozygous worm is placed in a dish with nutrients, the worm lays eggs, and after four days there are a total of 12 larvae. How many of these larvae do you expect to have the genotype (lit-1+/+)? How many will have the (lit-1/+) genotype? How many will have the (lit-1/lit-1) genotype? (1 point)

Answer 1

1) a) genotype of the heterozygous plants is Pp

Pp * Pp

	P	p
P	PP ( purple flowers)	Pp ( purple flowers)
p	Pp ( purple flowers)	pp ( white flowers)

the expected ratio is

purple flowers: white flowers = 3:1

there are 36 progenies

the expected number of plants with purple flowers= total number of plants $\times$ ( number of expected plants with purple flowers/total number of plants)=36$\times$3/4= 27.

the expected number of plants with white flowers= total number of plants $\times$ ( number of expected plants with white flowers/total number of plants)=36$\times$1/4= 9.

b) expected number of purple-flowered plants - observed number of plants with purple flowers=27-25=2

the observed number of white-flowered plants- expected number of purple-flowered plants= 11-9=2

so the difference between expected and observed purple-flowered plants=2

difference between expected and observed white-flowered plants=2