Question

1. You are studying 2 genes in Drosophila Melanogaster (fruit flies), Gene A and Gene B. Gene A and Gene B are located on different chromosomes and therefore will undergo independent assortment. Both genes have two different alleles, a dominant allele and a recessive allele. For example: for Gene A there is a dominant allele A and a recessive allele a. Gene A determines body color and gene B determines eye color. In terms of body color, some of your flies are purple and some of your flies are yellow. Purple is dominant to yellow. Gene B determines eye color, some of your flies have red eyes and some of your flies have brown eyes. Red is dominant to brown.

   You cross two individuals with the following genotypes: AABB X aabb. All of the offspring of this initial cross have the genotype AaBb. Next, you take two of the offspring from the initial cross and cross them. So, you just did the following cross AaBb X AaBb.

   What fraction of the offspring from the cross AaBb X AaBb will have yellow bodies?

   		3/16
   		9/16
   		1/4
   		3/4
   		none of the above

2. You are studying gene A and gene C in Drosophila Melanogaster (fruit flies). Gene A and Gene C are located on the same chromosome, which is an autosome, and crossing over never occurs between these two genes. Both genes have two different alleles, a dominant allele and a recessive allele. Again: for Gene A there is a dominant allele A and a recessive allele a. Gene A determines body color and gene C determines wing type. In terms of body color, some of your flies are purple and some of your flies are yellow. Purple is dominant to yellow. Gene C determines wing type, some of your flies have long wings and some of your flies have short wings. Long is dominant to short.

   You cross two individuals with the following genotypes: AAcc X aaCC. All of the offspring of this initial cross have the genotype AaCc. Next, you take two of the offspring from the initial cross and cross them. So, you just did the following cross AaCc X AaCc.

   In the last cross, AaCc X AaCc, what fraction of the offspring will have yellow bodies and long wings?

   		3/16
   		9/16
   		1/4
   		3/4
   		none of the above

3. You are studying a gene in humans that is located in the mitochondrial DNA.   A mutant form of this gene causes a disease we will call disease D. If a mother with disease D and a father who does not have disease D have 4 children, how many of their children would you predict have the disease?

   		0%
   		25%
   		50%
   		75%
   		100%

4. Researchers on Planet X have discovered a variety of seaweed. Some specimens glow in the dark, while others are completely colorless. Biochemists later find that two distinct gene products are needed to form the bioluminescent protein that makes some specimens glow. The glowing protein is formed according to the following scheme:

   Gene B codes for Enzyme B and their are two forms of this gene, a dominant allele B and a recessive allele b. The dominant allele codes for a functional Enzyme B, while the recessive allele codes for a nonfunctional Enzyme B.  Gene R codes for Enzyme R and their are two forms of this gene, a dominant allele R and a recessive allele r. The dominant allele codes for a functional Enzyme R, while the recessive allele codes for a nonfunctional Enzyme R. For both genes, having only one dominant allele is sufficient to produce functional enzyme.

   Given the information above, which of the following types of seaweed would glow? Make sure to read all of the choices.

   		BBrr
   		BBRR
   		BbRr
   		bbRR
   		bbRR and BBrr
   		BBRR and BbRr

5. You discover that gene P, gene I and gene R are on the same chromosome in Drosophila Melanogaster. When you do genetic crosses following the inheritance of gene P and gene R you get 1000 offspring and 300 of them are recombinants. When you do genetic crosses following the inheritance of gene P and I you get 1000 offspring and 100 of them are recombinants. When you do genetic crosses following the inheritance of gene R and I you get 1000 offspring and 200 of them are recombinants. Which two genes are the closest together?

   		P and R
   		R and I
   		P and I

Answer 1

Answer – 1/4

Description –

Gene A (body color) alleles – A (dominant, purple) , a (recessive, yellow)

Gene B (eye color) alleles – A (dominant, red) , a (recessive, brown)

Crossing of AaBb and AaBb

	AB	Ab	aB	ab
AB	AABB	AABb	AaBB	AaBb
Ab	AABb	AAbb	AaBb	Aabb
aB	AaBB	AaBb	aaBB	aaBb
ab	AaBb	Aabb	aaBb	aabb

AABB – 1, AAbb – 1, aabb – 1, aaBB – 1, AABb – 2, Aabb – 2, AaBB – 2, aaBb – 2, AaBb – 4

aabb(1), aaBB (1), aaBb (2) will be having yellow bodies.

Summing up the above data 4/16 are having yellow bodies. Therefore, the answer is ¼.

Answer – None of these.

Description –

Since gene A and gene C are located on same chromosome, they never cross each other.

Therefore alleles of AaCc will be only AC and ac

Crossing of AC and ac

	AC	ac
AC	AACC	AaCc
ac	AaCc	aacc

To have yellow bodies and long wings we need aaCC or aaCc. But none of those are obtained due to alleles being on same chromosome. Therefore, the answer is None of these.

Answer – 100%

Description – The mDNA of mother is always transmitted to the offspring and never father’s. Therefore any mutation in mDNA of mother passes to their offspring. In this case since mother is having mutation which causes disease D, her all 4 children will have this disease.

Answer – BBRR and BbRr

Description – The seaweed will flow only if it is having dominant gene B and dominant gene R. This is because they produce functional enzyme B and R which are together responsible for glowing trait.

Therefore, from the given options BBRR and BbRr is the correct answer.

Answer – P and I

Description – Genes linked on chromosome shows least recombinant results over crossing. If the genes are closely linked, the recombinants will be less than genes located far on same chromosome. Since the recombinants of gene P and I are 100 out of 1000 which is least among the given options of recombinants, our answer is P and I.