1. Since they are attached to the same chromosome they would segregate together as a group. This would explain why individuals with red hair usually are prone to have freckles. In the example above if allele "R" is linked to "l" than where ever the "R" allele goes the "l" must go. When working problems concerning linked genes you would use the same method that you used in solving monohybrid problems. You will have no more than two different types of gametes..
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2. How many genes make up the human genome?
Several thousands. How many different types of chromosomes are present
in human cells? There are 46 chromosomes which are in pairs; therefore,
there are 23 different types of chromosomes on which these thousands of
chromosomes must be attached. If you were to choose two genes to
study, the chances are pretty good that they will be linked.
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AaBb x AABb
3. Both parents have red hair and facial freckles (phenotype). One parent is heterozygous for both traits and the other is homozygous for hair color and heterozygous for the presence of facial freckles.
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4. In parent 2, where allele "A" goes allele "b" will go and where allele "A" goes "B" goes.
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5.
| /////////////////////////////////////////////// | A
|
| B | |
a |
| b | |
|
A |
| b | |
A
|| A
|| b || B |
A || a
|| b || b |
|
A |
| B | |
A
|| A
|| B || B |
A || a
|| B || b |
Note the top row and first column are haploid and the four cells inside are diploid.
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6. Cell 1 has the genotype AABb, cell 2
has the genotype AABB, cell 3 has the genotype Aabb and cell four has the
genotype AaBb.
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7.
C | | c
c | | c
| |
x
| |
D | | d
d | | d
Parent 1
Parent 2
| /////////////////////////////////////////////// | c |
| d | |
c |
| d | |
|
C |
| D | |
C || c
|| D || d |
C || c
|| D || d |
|
c |
| d | |
c || c
|| d || d |
c || c
|| d || d |
The phenotype ratio for these two parents would be 1 CcDd to 1 ccdd. or one half of the offspring would have the dominant trait for both genes (widow's peak and middigital hair) and and one half would have the recessive trait for both genes (straight hairline and no middigital hair).
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8. Parents:
CcDd X ccdd
| ///////// | CD | Cd | cD | cd |
| cd | CcDd | Ccdd | ccDd | ccdd |
| cd | CcDd | Ccdd | ccDd | ccdd |
If these alleles were not linked their would b four different types of phenotypes:
1 would be CcDd or widow's peak and middigital hair, 1 would be Ccdd or widow's peak and no middigital hair, 1 would be ccDd or straight hairline and middigital hair and 1 would be ccdd or straight hairline and no middigital hair. Place the correct answer in your notes.
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9. The ratio when these genes are located on the
same chromosome is 1 CcDd to
1 ccdd.
The ratio when these gene
are not located on the same chromosome is 1 CcDd
to 1 Ccdd
to 1 ccDd to 1 ccdd.
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10. The genotype of the individual
would be:
C | | c
||
d || D
diploid
The genotypes of the non crossover gametes would be:
C |
| c
| and
|
d |
| D
haploid
The genotypes of the
crossover gametes would be:
C |
| c
| and
|
D |
| d
haploid
The ratio of the gametes
produced by this individual would be:
C |
| c
C |
c |
46% =
| 46% = |
4% = |
4% = |
d |
| D
D |
d |
Draw these in you notes and study.
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Created by the Center for Learning Technologies, Academic Technology Services.
Last modified October 22, 1997.