Bio 209, Dr. Fernandez.




1.      Your ability to roll your tongue is controlled by two alleles that segregate according to Mendel’s segregation principle. The allele for being able to roll your tongue (R) is dominant. The allele for not being able to roll your tongue (r) is recessive. In a cross between two parents who are both heterozygous for the tongue-rolling trait, what will the phenotypic ratio of the offspring be?


2.      Large Kings (W) is a dominant trait in dragons. Small Kings (w) is recessive. If both parents are heterozygous for wing size, what is the probability that an offspring will have small wings?


3.      In a gene for cystic fibrosis, CF+ represents the dominant healthy allele and CF- the recessive disease allele. Human eye color is usually inherited as if the allele for brown eyes (B) is dominant and the allele for blue eyes (b) is recessive. In a cross in which both parents are heterozygous for cystic fibrosis and eye color, what would the phenotypic ratio for the offspring be if the alleles sorted independently?


4.      Red eyes (R) is dominant trait in dragons; green eyes (r) is recessive. Large wings (W) is a dominant trait; small wings (w) is recessive. If the alleles for eye color sort independently, what phenotypic ratio of offspring will be produce by this cross?


5.   For each of the individuals with genotypes below list all the different (and only different) possible gametes. Do not use unneeded lines.

a) AABb

______ ______ ______ ______ ______ ______ ______ ______

b) aaBbtt

______ ______ ______ ______ ______ ______ ______ ______

c) DdEeGg

______ ______ ______ ______ ______ ______ ______ ______

d) MmNNRrYy

______ ______ ______ ______ ______ ______ ______ ______



6.     You have two bean plants from truebreeding stocks. One plant has red flowers and is short. The other has white flowers and is very tall. Using the letter “R” (both upper and lower case) for flower color, and “T” (upper and lower case) for tallness, write out the genotype of the two parent plants and the genotype and phenotype of the F1 offspring.


a) If red is dominant to white, and tall is dominant to short.

Parent 1:

Parent 2:



b) If red is incompletely dominant to white. In this case a plant heterozygous for the R genes will be pink. Tall is still dominant.

Parent 1:

Parent 2:



c) Do a Punnett square showing the genotypes and phenotypes for the F2 generation from b).


















7.  Joe is genotype Ee for an enzyme found in blood. He is phenotypically normal. However, chemical analysis of Joe’s blood shows that he has less of the enzyme than Vincent, who is genotype EE and is also phenotypically normal. Is the production of this enzyme a trait that shows complete or incomplete dominance? Explain your answer


8.   Recall that widow’s peak and free earlobes are dominant traits. Latoya has a widow’s peak and free earlobes. Dennis has a widow’s peak and attached earlobes. They have two children: one has a widow’s peak and attached earlobes, and the other has a straight hairline and attached earlobes.

What are the genotypes of Latoya and Dennis?


Considering earlobes only, what fraction of their children would be expected to have free earlobes?


Does the fact that they have no children with free earlobes mean that earlobe inheritance is not a simple Mendelian trait? Explain.


9.     Congenital night blindness is caused by a dominant autosomal allele B.  A man is heterozygous for night blindness.  What is his genotype?____________ Is he night blind?___________.  His wife is normal for the trait.  What is her genotype__________.  What is the probability that their first-born child will have night blindness? __________. What is the probability that their second born child will have night blindness?_________. 


10.   The ABO blood system in humans is governed by three alleles: IA is the blood type A allele, IB is the blood type B allele, and i is the blood type O allele. IA and IBare codominant, while i is recessive. In a family of four children, one has Type O blood, one has Type AB blood, one has Type B blood, and one has Type A blood. Do a Punnett square showing the possible genotypes of the parents.

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