Question

1. What gametes are produced by the following organisms:
   1. Genotype YyRr, if Y and R are on different chromosomes
   2. Genotype YyRr, if dominant Y and R are on the same chromosome, no crossing over
   3. Genotype YyRr, if dominant Y and recessive r are on the same chromosome, no crossing over
   4. Genotype YyRr, if dominant Y and R are on the same chromosome, 50% crossing over
2. Draw a dihybrid cross between two tall plants with yellow seeds TtYy. Use a 5x5 table or insert a picture. Which phenotypes are most and least common?
3. In a cross between AaBbCcDD and AabbCCDd, what is the probability of an offspring with the phenotypes or genotypes below? Show math.
   1. Phenotype Dominant A, Dominant B, Dominant C, and Dominant D
   2. Phenotype Recessive A, Recessive B, Dominant C, Dominant D
   3. Phenotype Recessive A, Recessive B, Recessive C, Recessive D
   4. Genotype aaBbCcDD
   5. Genotype AAbbCCDd
   6. Genotype AabbCCdd
4. Genes A, B, and C are on different chromosomes. A heterozygous organism AaBbCc therefore carries each homologous gene pair (e.g. A and a) on a separate chromosomes. Draw (insert a picture) or describe how these chromosomes align at the metaphase plate in metaphase I in mitosis and meiosis for the three pairs.
5. A red-eyed female Drosophila whose father was white-eyed is crossed with a white-eyed male Drosophila. Draw the cross (use a 3x3 table) or insert a picture. Describe the phenotypes (eye color, sex) of the offspring.
6. In Barbara McClintock and Harriet Creighton’s experiment with corn there are eight possible progeny. What is special about the corn with the colorless waxy (c/wx) phenotype? How else was the experiment confirmed?

Answer 1

1).

Genotype YyRr, if Y and R are on different chromosomes produces 4 types of gametes, YR, Yr, yR & yr.

2).

Genotype YyRr (Yr/yR), if Y and R are on different chromosomes produces only two types of gametes, Yr & yR.

3).

Genotype YyRr (YR/yr), if Y and R are on different chromosomes produces only two types of gametes, YR & yr.

4).

Genotype YyRr, if dominant Y and R are on the same chromosome, 50% crossing over produces 4 types of gametes, YR, Yr, yR & yr.

5).

TtYy x TtYy ---Parents

	TY	Ty	tY	ty
TY	TTYY (tall, yellow)	TTYy (tall, yellow)	TtYY (tall, yellow)	TtYy (tall, yellow)
Ty	TTYy (tall, yellow)	TTyy (tall, green)	TtYy (tall, yellow)	Ttyy (tall, green)
tY	TtYY (tall, yellow)	TtYy (tall, yellow)	ttYY (dwarf, yellow)	ttYy (dwarf, yellow)
ty	TtYy (tall, yellow)	Ttyy (tall, green)	ttYy (dwarf, yellow)	ttyy (dwarf, green)

Phenotypes:

Tall, yellow = 9/16

Tall, green = 3/16

Dwarf, yellow = 3/16

Dwarf, green = 1/16

Phenotypes that are most common = tall, yellow (9/16).

Phenotypes that are least common = dwarf, green (1/16)

6). AaBbCcDD x AabbCCDd –Parents

Aa x Aa = AA (1/4), Aa (1/2) & aa (1/4)

Bb x bb = Bb (1/2) & bb (1/2)

Cc x CC = CC (1/2) & Cc (1/2)

DD x Dd = DD (1/2) & Dd (1/2)

· Phenotype Dominant A, Dominant B, Dominant C, and Dominant D = (AA+Aa) * Bb * (CC+Cc) * (DD+Dd) = ¾ * ½ * 1 * 1 = 3/8

· Phenotype Recessive A, Recessive B, Dominant C, Dominant D = aa * bb * (CC+Cc) * (DD+Dd) = ¼ * ½ * 1 * 1 = 1/8

· Phenotype Recessive A, Recessive B, Recessive C, Recessive D = aa * bb * cc * dd = ¼ * ½ * 0 * 0 = 0 (zero)

· Genotype aaBbCcDD = ¼ * ½ * ½ * ½ = 1/32

· Genotype AAbbCCDd = ¼ *1/2 * ½ * ½ = 1/32

· Genotype AabbCCdd = ½ * ½ * ½ * 0 = 0 (zero)