# Order of alleles

I have a question from class where we have to write out the genotype of the triply heterozygous mother (given the frequency of the progeny). What I'm having trouble understanding is, how can it be determined what order to write the alleles in if the chromosome number isn't given or if it doesn't state if its sex-linked?

Is the dominant allele the one that occurs most often?

I've included the queston as an attachment.

Thanks.

In Drosophila melanogaster, the allele n gives notched wings while the wildtype allele n+ gives normal wings. At a separate gene, the allele sb gives stubby legs while wildtype sb+ allele gives normal legs. At a third gene, the allele w gives white eyes while wildtype w+ allele gives red eyes. A female individual heterozygous for these three genes is test crossed and 2000 progeny are produced. They are classified as follows (see attachment)

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Hi there,

this is actually not the easiest of genetics questions. Please see attached for my answer. In the document I answer only the question directly asked in the the assignment. ...

#### Solution Summary

A full solution is provided.

Biology Genetics Problem Set

See attached file for full problem description.

1. A man and woman marry who are both Rh+ and both heterozygous for the Rh factor. (Rh+ is dominant over Rh-.)

A. Give the genotypes of the parents. (2 points) Man ______________ Woman ______________

B. What is the probability that their first child will be Rh-? (2 points)

C. What is the probability of a Rh+ male or a Rh- female? (2 points)

D. What if the probability that they will have a Rh+ male, a Rh- female, and a Rh+ female? (2 points)

E. Calculate the probability of 2 Rh+ and 4 Rh- children? (4 points)

2. Red-green color blindness is X-linked recessive. MN blood type is determined by an autosomal gene with two codominant alleles, LM and LN. A woman whose father was color-blind has type MN blood. She is going to have a child with a man who has normal color vision and type MN blood.

What is the probability the child will be a boy, with normal color vision and type M blood? (5 points)

3. The accompanying pedigree is for a rare, but relatively mild, hereditary disorder of the skin.

A. What is the mode of inheritance for this rare skin disorder? Explain. (4 points)

B. Use appropriate genetic symbols and give the genotype of the following individuals (4 points)

I-1 _____ II-1 _____ III-2 _____ III-7

C. What is the probability that III-1 is heterozygous? (2 points)

D. If III-1 and III-8 marry:

(1) what is the probability that their first child will have the skin disorder? (2 points)

(2) what is the probability that their second child with be a normal male? (2 points)

4. The trait in the pedigree below is inherited as a single dominant gene.

A. What is the probability that II-1 is heterozygous? (2 points)

B. What is the probability of an affected child if the following cousins marry?

(1) III-1 and III-3 (2 points)

(2) III-2 and III-4 (2 points)

5. A student crossed lobed-eyed, tan-bodied female Drosophila with normal-eyed, black-bodied males. All the F1's were lobed-eyed and tan-bodied. She crossed the F1's and obtained the results given below.

Phenotype Number

lobed-eyed, tan-bodied 675

lobed-eyed, black-bodied 97

normal-eyed, tan-bodied 78

normal-eyed, black-bodied 150

A. Assume independent assortment and state the null hypothesis. (2 points)

B. Test your null hypothesis using chi-square analysis. (10 points)

6. In humans, right-handedness (L) is dominant to left-handedness (l). Assume a mating between 2 individuals that are heterozygous.

A. What is the probability that a child will be left-handed? (1 point)

B. If a child from this mating is right-handed, what is the probability that s/he is heterozygous? (2 points)

C. What is the probability of having a family of 3 right-handed and 1 left-handed children? (2 points)