Biology

Genetics Problems

        
                   
   

     
               
                         

Objectives for today:

* Use a Punnents square to determine probability of traits in offspring given traits of both the parents.
                 
    Monohybrid Cross: a cross concerned with only one trait.    
                         
     

Monohybrid sample problem:

* In roses, red is dominant over white.
* Use R for the red gene.
* Use r for the white gene.
* Cross two heterozygous red roses, Rr X Rr

* From the Punnett Square,

* describe the phenotype of the offspring.

* 3/4 Red
* 1/4 White

* describe the genotype of the offspring.

* 1/4 RR
* 1/4 rr
* 1/2 Rr

     
   
     
       
 
Dihybrid Cross: a cross concerned with two traits.      
       
 

Dihybrid sample problem:

* In mice, black is dominant over tan and short tails are dominant over long.

* Use B for black and b for tan.
* Use S for short and s for long.

* Write the genotype for a heterozygous black, short-tailed mouse.


* Cross two of these individuals.


* From the Punnett Square, describe the phenotype of the offspring.

* 9/16 Black - Short
* 3/16 Black - Long
* 3/16 Tan - Short
* 1/16 Tan - Long

   
 
   
       
         
 

 

20. Which of these Punnett Squares represents a cross involving incomplete dominance?

A. 1
B. 2
C. 3
D. 4

 

 
         
       
 

 

Hear your paper Unit 4 Day 5 Dihybrid Cross Practice.

Draw the Punnett Square required for each problem, then answer the questions about the offspring.


1 . Dihybrid cross:
In certain bacteria, an oval shape is dominant over round and thick cell walls are dominant over thin. Cross a heterozygous oval, thick cell walled bacteria with a round, thin cell walled bacteria. Describe the phenotype of the offspring.


2 . Dihybrid cross:
In guinea pigs, black coat color is dominant over white, and rough coat is dominant over smooth. Show the Punnett Square for a cross between a homozygous black, rough coat guinea pig and a homozygous white, smooth coat guinea pig. What do the offspring look like?