1 . Shell color in the Pacific abalone is controlled by a single gene with two a
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Question
1. Shell color in the Pacific abalone is controlled by a single gene with two alleles. The Green color allele (G) is dominant to the orange shell allele (g). Shell diameter is controlled by a different gene with two alleles - the Thick allele (T) is dominant to the thin allele (t). A mating between green shelled mollusks with thick shell diameter in a population of abalones produced offspring with the following genotypes in the following proportions:
What are the parents’ Genotypes in the cross?
Phenotype
Green shell,
Thick diameter
Green shell,
Thin diameter
Orange shell,
Thick diameter
Orange shell,
Thin diameter
Number
450
189
212
74
a) Thinking about this cross and assuming no recombination and a diploid number of 4, draw two possible arrangements of the chromosomes at metaphase in Meiosis I below. Draw your chromosomes as indicated in the example, with the “X” referring to the allele it carries. (2 pts.) You will have alleles for shell color and shell diameter: G or g and T or t
Possible arrangement 1 Possible arrangement 2
Example:
If replicated
If not replicated
b) Which of Mendel's Laws is illustrated by these possible arrangements? What would be the effect on the number of possible arrangements of having a larger diploid number of chromosomes? (2 pts)
2. (3 pts) Gametic diversity.
a) A diploid cell with two chromosome types, so 2n = 4, undergoes meiosis. Assuming that meiosis proceeds normally and that chromosomes assort independently, but assuming that there is no recombination, how many different types of gametes are possible? That is, how many different chromosome combinations are possible for the gamete? _______________
b) Answer the same question as in a) but this time assume that 2n = 8. How many different chromosome combinations are possible for a gamete? _____________________________
c) Based on questions a-b and the pattern you see between the number of chromosome types and the number of gametes possible, give a generalized formula for the relationship between the number of chromosome types (n) and the number of gametes possible.
G = ____________________________
3. What is segregation, and why is it important to Darwin's mechanism of evolution by natural selection? (1 pts.)
4. A species of centipede has a haploid chromosome number of 2. Leg length is controlled by a single gene with two alleles: the long leg allele (L) is dominant to the short leg allele (l). Body coloration is controlled by a single gene with two alleles: the dark allele (D) is dominant to the light allele (d). Leg length and body coloration are encoded by genes on separate chromosomes. Assume the traits obey Mendel’s law of Independent Assortment.
a) A centipede that is homozygous for the recessive allele at both loci mates with a centipede that is homozygous for the dominant allele at both loci. They produce 100 offspring. What fraction of the offspring would you expect to have short legs and light body coloration? Show your calculations and reasoning. (2 pts.)
b) Two centipedes that are each heterozygous for both leg length and body coloration mate and produce 100 offspring. What fraction of the offspring would you expect to have long legs and light body coloration? Show your work using a Punnett Square and provide your answer as a fraction. (2 pts.)
5. In a species of assassin bugs, two alleles of one gene determine the character difference of long versus short antennae, and two alleles of a separate, independent gene determine the character difference of red versus black exoskeleton. The phenotype results for four separate matings (each involving different parents) between bugs are shown below.
Offspring Phenotypes
Mating
Parental Phenotypes
long/
black
long/
red
short/
black
short/
red
1
long/red x short/black
91
94
89
90
2
long/red x short/black
398
0
0
0
3
long/black x short/red
208
211
0
0
4
long/black x short/black
200
0
207
0
a) Assign a letter to each allele (make sure each allele can be uniquely identified, using either uppercase and lowercase and/or using a unique letter for each allele). Circle whether each allele is dominant (D) or recessive (R). (2 pts.)
letter assignment Dominant/Recessive? (circle one)
Antennae length gene:
long _________ D R
short _________ D R
Exoskeleton color gene:
red _________ D R
black _________ D R
b) What are the genotypes of each parent in each cross? If more than one genotype is possible, list the alternative possibilities. (Remember that each mating involved a separate set of parents, so the 4 matings involved 8 separate parents in total). (4 pts.)
Mating
Phenotype of Parent # 1
Genotype
of Parent #1
Phenotype of Parent #2
Genotype
of Parent #2
1
long/red
short/black
2
long/red
short/black
3
long/black
short/red
4
long/black
short/black
6. In daisies, thick stems (T allele) is dominant over thin stems (t), and white flowers (W)
is dominant over yellow flowers (w). These genes show independent assortment. When
a cross is made between a plant that is homozygous for both thick-stem, white flowers
and a plant that has thin stems and yellow flowers, what is the probability that they have offspring with yellow flowers and thick stems? Show your work and explain your reasoning. (3 pts.)
7. Marfan syndrome is a human disorder causing defects in the lens of the eye, excessively lengthy fingers and toes, and characteristic defects of the heart. It results from the presence of a dominant allele. If a man with Marfan syndrome (who has an unaffected mother) has a child with a woman who does not have this disorder but whose mother did, what is the probability that their child will have the disease? (2 pts.)
8. A man, Waldo, whose sister died in early childhood from a recessive lethal disease marries a woman, Ethel, with the same family history. Because this man survived beyond childhood, he does not have the disease, but he may be a carrier ( = heterozygous, as may also be the case with his wife). What is the probability that their first child will suffer from the disease? [Hint: first calculate the probability that Waldo is heterozygous; then determine the probability that both parents are carriers. Remember that he has survived to adulthood when calculating this probability]. (2 pts.)
9. The pedigree shown below is a mammalian pedigree. Females are represented by circles and males by squares. Unaffected individuals are represented by unshaded symbols and people with the trait are represented by shaded symbols. This trait is NOT sex linked.
For this pedigree, indicate whether a recessive or dominant mode of heritability is more likely. Explain your reasoning. (2 pts.)
10. Below is a pedigree for the trait Duchenne muscular dystrophy, a sex-linked recessive trait that results in muscle degeneration. What is the probability that if A and B have children, they will have two boys, both of whom exhibit Duchenne muscular dystrophy? (3 pts.)
Phenotype
Green shell,
Thick diameter
Green shell,
Thin diameter
Orange shell,
Thick diameter
Orange shell,
Thin diameter
Number
450
189
212
74
Explanation / Answer
1. The given number of progenies were showing near about pattern of 9:3:3:1 which comes when the parents were heterozygous for both the genes. So the genotype of the parent will be : GgTt & GgTt
In question's next part there is reference of an example which is not visible. So can't answer further parts.
2. In case there is no recombination, the gametes produced will be of parental type only.
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