Download Name: Date Period Genetic Crosses Directions: Complete each

Name:
Date
Period
Genetic Crosses
Directions: Complete each Punnett square and list all possible genotypes, phenotypes and ratios for each
cross where needed.
Sickle-cell anemia is an autosomal recessive genetic disorder that causes red blood cells to change shape and
can cause the red blood cells to become stuck in blood vessels. This blocking can deprive tissues of oxygen and
cause organ damage like strokes. One benefit of it is that people who has one or two alleles of the sickle cell
disease are resistant to malaria since red blood cells are not conducive to parasites. Sickle-cell anemia also
exhibits incomplete dominance at which the individual who does not have the disease retains immunity to
malaria. Fill in the punnett square and determine the expected genotypic and phenotypic ratios from crossing
homozygous recessive and homozygous dominant parents.
Genotypes:
Genotypic Ratio:
Phenotypes:
Phenotypic Ratio:
Hemophilia A is a recessive sex-linked genetic disorder that prevents the blood from clotting. The effects of the
X chromosome disorder develop almost entirely in males even though the gene is inherited from one of the
mother’s X chromosomes. Fill in the punnett square and determine the expected genotypic and phenotypic
ratios from crossing a male with Hemophilia A with a female who is a carrier for hemophilia.
Genotypes:
Phenotypes and ratio:
Red-Green color blindness is a recessive sex-linked (X chromosome) genetic disorder where the middle (green)
or long (red-yellow) wavelength cones in the eyes have a partial or complete loss of function. Fill in the
punnett square and determine the expected genotypic and phenotypic ratios from crossing a normal male and a
female who is a carrier of color-blindness.
Genotypes:
Phenotypes and ratio:
Blood type A and B are dominant over type O. Fill in the punnett square and determine the expected genotypic
and phenotypic ratios from crossing a person who has heterozygous types B and a person who has heterozygous
types A.
Genotypes:
Phenotypes and ratio:
In Labrador retriever dogs, the gene B (dominant) produces black coat color (BB or Bb; black Lab), with the
homozygous recessive condition (bb) producing brown Lab. The dominant epistatic gene E controls the
presence of coat color. The homozygous recessive ee condition prevents the deposition of coat color, resulting
in a golden Lab (regardless of whether the coat color is black - BB or Bb or brown – bb). Complete the punnett
square for this cross BbEe x bbee.
Genotypes:
Phenotypes and ratio:
An aquatic arthropod called a Cyclops has antennae that are either smooth or barbed. The allele for barbs is
dominant. In the same organism, resistance to pesticides is a recessive trait. A Cyclops that is resistant to
pesticides and has smooth antennae is crossed with one that is heterozygous for both traits. Show the genotypes
of the parents. Set up a punnett square for the cross.
Genotypes:
Phenotypes and ratio:
In humans there is a disease called Phenylketonuria (PKU) which is caused by a recessive allele. People with this allele
have a defective enzyme and cannot break down the amino acid phenylalanine. This disease can result in mental
retardation or death. Let “E” represent the normal enzyme. Also in humans in a condition called galactose intolerance or
galactosemia, which is also caused by a recessive allele. Let “G” represent the normal allele for galactose digestion. In
both diseases, normal dominates over recessive. Set up a punnett square for the cross. If two adults were heterozygous
for both traits, what are the chances of having a child that is completely normal? Has just PKU? Has just galactosemia?
Has both diseases?
Genotypes:
Phenotypes and ratio: