Monohybrid crosses


1. In dogs, wire hair (S) is dominant to smooth (s). In a cross of a homozygous wire-haired dog with a smooth-haired dog, what will be the phenotype of the F1 generation?
 

 
 
 

What would be the genotype?
 

 
 
 

What would be the ratio of wire-haired to smooth-haired dogs in the F2 generation ?
 


2. Woodrats are medium sized rodents with lots of interesting behaviors. You may know of them as packrats. Let's assume that the trait of bringing home shiny objects (H) is controlled by a single locus gene and is dominant to the trait of carrying home only dull objects (h). Suppose two heterozygous individuals are crossed. How many of each genotype would be expected if only 4 offspring were produced?
HH:
Hh:
hh:


 
 
 

How many of each phenotype?
 
Brings home shiny objects:
Brings home dull objects:


3. Saguaro cacti are very tall cylindrical plants that usually have two L-shaped arms, one on each side. Suppose you lived in southern Arizona where the Saguaro cactus is common and you happen to have one growing in your yard. Your Saguaro has two arms but one is longer than the other. Now, assume that arm length in these cacti are controlled by a single gene with arms of the same length (A) being dominant to arms of different lengths. What is the genotype of your cactus?
 

 
 
 

Could one of the parents of your cactus have had a phenotype with arms the same length?
 

 
 
 

If so, what would have been the genotype of that parent?
 

 
 
 

Suppose you cross your cactus with that of your neighbor which has arms of the same length. Your great grandchildren (it takes a Saguaro cactus a long time to mature) find that half of the resulting offspring have arms the same length and half have arms of different lengths. What was the genotype of your neighbor's cactus?
 


4. The common grackle is a species of robin-sized blackbirds that are fairly common (hence the name) over most of the United States. Suppose that long tails (L) were dominant to short tails in these birds. A female short-tailed grackle mates with a male long-tailed grackle who had one parent with a long tail and one parent with a short tail. What is the male's genotype?
 

 
 
 

How many of each genotype will be found in the F1 generation (assume 4 offspring)?
 
LL:
Ll:
ll:


 
 
 

How many of each phenotype will be found in the F1 generation?
 
Long tail:
Short tail:


5. The ability to curl your tongue up on the sides (T, tongue rolling) is dominant to not being able to roll your tongue. A woman who can roll her tongue marries a man who cannot. Their first child has his father's phenotype. What are the genotypes of the mother, father, and child?

Mother:
 

 

Father:
 

 

Child:
 

What is the probability that a second child won't be a tongue roller?
 


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