12.3: Linked Genes

Which genes are most likely linked?

• genes 1 & 2
• genes 2 & 3
• genes 3 & 4
• genes 1 & 4

The reason some linked genes may get separated during gamete formation is - - - 

• genes aren't on the same chromosome
• genes don't compliment each other well
• a crossing over event shuffles the genes
• an environmental impact forces the genes to shuffle

Given the crossover frequency of each of the following genes, construct a chromosome map.  
Gene    Frequency of Crossover
A-C            30%
B-C            45%
B-D            40%
A-D            25%

• A - B - C - D
• B - D - A - C
• B - A - D - C
• C - A - D - B

 CROSS I. Purebred lines of wild-type fruit flies (gray body and normal wings) are mated to flies with black bodies and vestigial wings.    F1 offspring all have a normal phenotype. 
 CROSS II. F1 flies are crossed with flies recessive for both traits (a testcross).
 Result. Offspring          Normal   Percent
 Gray body; normal wings  585     26.1
Black body; vestigial wings 581   25.9
Black body; normal wings  567    24.2
Gray body; vestigial wings  558   25.8
Based on the above information, choose the best answer for the following statement:
Vestigial wings are a recessive trait

• CROSS I results give evidence supporting the statement.
• CROSS I results give evidence against the statement.
• CROSS II results give evidence supporting the statement.
• CROSS II results give evidence against the statement.  

The recombination frequency between gene F and gene G is 10.4%, the recombination frequency between gene F and gene H  is 8.0%, and the recombination frequency between gene G and gene H is 18.4%. Which is the correct arrangement of these genes?  

• FGH
• FHG
• GHF
• HFG 

 CROSS I. Purebred lines of wild-type fruit flies (gray body and normal wings) are mated to flies with black bodies and vestigial wings.    F1 offspring all have a normal phenotype. 
 CROSS II. F1 flies are crossed with flies recessive for both traits (a testcross).
 Result. Offspring          Normal   Percent
 Gray body; normal wings  575     25.1
Black body; vestigial wings 571   24.9
Black body; normal wings  577    25.2
Gray body; vestigial wings  568   24.8
Based on the above information, choose the best answer for the following statement:
An F1 cross should produce flies that will fall into a Mendelian 9:3:3:1 ratio.  

• CROSS I results give evidence supporting the statement.
• CROSS I results give evidence against the statement.
• CROSS II results give evidence supporting the statement.
• CROSS II results give evidence against the statement.  

 CROSS I. Purebred lines of wild-type fruit flies (gray body and normal wings) are mated to flies with black bodies and vestigial wings.    F1 offspring all have a normal phenotype. 
 CROSS II. F1 flies are crossed with flies recessive for both traits (a testcross).
 Result. Offspring          Normal   Percent
 Gray body; normal wings  575     25.1
Black body; vestigial wings 571   24.9
Black body; normal wings  577    25.2
Gray body; vestigial wings  568   24.8
Based on the above information, choose the best answer for the following statement:
The genes for body color and wing shape are linked. 

• CROSS I results give evidence supporting the statement.
• CROSS I results give evidence against the statement.
• CROSS II results give evidence supporting the statement.
• CROSS II results give evidence against the statement.