Three Point Linkage Problems
1. Purebred male white mice with short tails and big ears are crossed to purebred black mice
with long tails and small ears. All of the progeny are black, with short tails, and big ears.
These progeny are crossed with white mice with long tails and small ears. The results of
this second cross are given below.
Fur color
White
White
White
White
Black
Black
Black
Black
Tail length
Short
Short
Long
Long
Short
Short
Long
Long
Ear size
Big
Small
Big
Small
Big
Small
Big
Small
Number of Progeny
666
14
6
314
314
6
14
666
a. Define the inheritance pattern of each trait
Fur color: Dominant = _______________
Recessive = ________________
- Represented by the letter __________
Tail Length: Dominant = _______________
Recessive = ________________
- Represented by the letter __________
Ear size: Dominant = _______________ Recessive = ________________
- Represented by the letter __________
Using the letters you just assigned:
What are the parental chromosomes?
Which chromosomes represent the double crossovers?
Which gene is in the center of the other two?
Draw a map of your chromosome below. Then use the data to calculate the distances between
each gene. SHOW YOUR WORK.
2. In garden peas, the following cross was made between purebred plants.
tall, red flower, round seed
X short, white flower, wrinkled seed
The progeny were all medium height, pink flowered, wrinkled seed. These progeny peas were
crossed to short, white flowered, round seed peas. The results of this cross were:
Height
Color
Seed
Number of Progeny
Short
White
Wrinkled
340
Short
Pink
Wrinkled
340
Medium
White
Round
340
Medium
Pink
Round
340
Medium
White
Wrinkled
160
Medium
Pink
Wrinkled
160
Short
White
Round
160
Short
Pink
Round
160
b. Define the inheritance pattern of each trait
Fur color: Dominant = _______________
Recessive = ________________
- Represented by the letter __________
Tail Length: Dominant = _______________
Recessive = ________________
- Represented by the letter __________
Ear size: Dominant = _______________ Recessive = ________________
- Represented by the letter __________
What type of cross was done to get the F2 generation?
What are the expected ratios of phenotypes?
Are these genes linked? Explain. If so, map out your genes and calculate the distance
between them.
3. In warthogs, the following autosomal map has been determined.
Tusk
5 m.u.
hair______10 m.u.
Face
The trait variations for the genes are as followed:
Tusk: points up or out
Hair: long or short
Face: ugly or uglier
A purebred up tusked, long haired, ugly boar is crossed with a purebred out tusked, short
haired, uglier sow. The piglets have upturned tusks, medium hair, are uglier. What are the rules
of expression (inheritance patterns) for these genes? (which is dominant, which is recessive)
The piglets grow up, and someone is foolish enough to let them breed. 80 offspring are
produced. What gametes are made and in what frequency? (in other words, work backwards.
You are filling numbers into the data chart that we usually give you!)
4. In the flowering plants called Four O'clocks, there is a single gene controlling flower color,
another controlling leaf color, and a third controlling height. The following cross is done.
Purebred White flowers, green leaves, short plants
X
Purebred Red flowers, purple leaves, tall plants
F1
Pink flowers, purple leaves, tall plants
The F1 plants were crossed to short plants with red flowers, green leaves. The progeny of this
cross are:
Flower
Leaves
Height
36% Red
purple
tall
36% Pink
green
short
9% Red
green
9% pink
purple
short
4% Red
green
short
4% pink
purple
tall
1% red
1% pink
purple
green
tall
short
tall.
A. Define the rules of expression for these alleles of these genes. Make sure you define your
symbols clearly.
B.
Define the linkage relationships for these genes.