Download You hypothesize that you have one autosomal dominant trait

AP Lab #7: Genetics of Organisms
Pre-Lab 2 Problems
Read each question carefully. Use the 2 statistical test to determine if the various hypotheses
regarding patterns of inheritance are supported. On a separate sheet of paper, show all work for each
question and put a box around your answer.
1. You hypothesize that you have one autosomal dominant trait. You crossed the following true
breeding parents: wild type female and mutant male. In the F2 generation you observe the
following phenotypes: 35 dominant females, 35 dominant males, 20 recessive males, and ten
recessive females. Show your chi-square calculations, and is your hypothesis supported?
2. You are studying hair length in wild yaks and perform the standard genetic crosses. You suspect
that the short hair allele is sex-linked recessive. In the following observations, assume both
parents are true breeding. Test your hypothesis with a Chi-square test. Show all your calculations
for the Chi-Square.
P: short haired male X long haired female
F1: 145 long haired males and 155 short haired females
(F2 is a cross of F1 male and female)
F2: 73 long haired females; 77 short haired females; 72 long haired males, 78 short haired
males.
3. You are analyzing a dihybrid cross where both mutant traits are autosomal recessive in a Scooby
Doo species. You set up the cross with each true breeding parent exhibiting one wild type trait.
You observe A = brown, a = gray and M = munchies, m = no munchies. In the F2 generation you
observe 152 brown munchie having scoobys, 48 brown no munchie having scoobys, 42 grey
munchie having scoobys and 12 grey no munchie having scoobys. Test your hypothesis with a
Chi-square test. Show all your calculations for the Chi-Square.
4. Suppose that a cross between two pea plants yields a population of 880 plants, 639 with green
seeds and 241 with yellow seeds. You are asked to propose the genotypes of the parents. Your
hypothesis is that the allele for green is dominant to the allele for yellow and that the parent
plants were both heterozygous for this trait. If your hypothesis is true, then the predicted ratio of
offspring from this cross would be 3:1 (based on Mendel's laws) as predicted from the results of
the Punnett square. Test your hypothesis with a Chi-square test. Show all your calculations for
the Chi-Square.
5. In sweet peas, purple flowers (A) are dominant to white (a). However, a second gene codes for
an enzyme involved in pigment production; at least one copy of the dominant allele for this gene
(B) must be present for purple flowers to be possible. In other words, bb plants have white
flowers even if they are AA or Aa.
Two purple-flowered plants that are AaBb are crossed: AaBb x AaBb. Their offspring are used
to establish a population. After a number of generations for that population, you randomly
sample 100 plants and count 58 purple-flowered plants and 42 white-flowered plants. Calculate
chi-square for distribution of flower color. What are your degrees of freedom? What percentage
of the time would you expect this deviation due to chance?
6. In Drosophila, eye color is an X-linked trait, and females are XX while males are XY. The
alleles for eye color are:
XR = red eyes (dominant)
Xr = white eyes (recessive)
Y = no allele (Y chromosome)
Your oh-so kind biology teacher gives you a male fly and a female fly as gifts, and you decide to
start a colony:
Parents
XRXr x Xr Y
You allow the offspring of these parents to interbreed, and continue interbreeding for several
generations. Soon your population reaches over 1000 flies. You take a random sample of 100
flies and observe:
30 red-eyed females
28 red-eyed males
22 white-eyed females
20 white-eyed males
Do the following:
Calculate chi-square value for your results (combined calculation for both eye color and sex).
What are your degrees of freedom?
What percentage of the time would you expect this deviation due to chance?