Hereditary Handout
Term
Gene
Allele
Purebred (homozygous)
Hybrid (Heterozygous)
Dominant Trait
Recessive Trait
Genotype
Phenotype
Parental Generation (P)
First filial Generation (F1)
Second filial generation (F2)
Monohybrid Cross
Dihybrid cross
Law of segregation
Law of independent
assortment
Polygenic traits
Test cross
Autosomal traits
Incomplete dominant traits
Sex-linked traits
Punnett square
Pedigree
Codominant traits
Name: ________________________________ Date: _______ Pd: ______
Definition
Visual
1.
The contrasting traits for hair color in guinea pigs are black (B) and white (b). What are the geneotypes and phenotypes
possible for hair color?
2.
Green (G) is the dominant color for pods of pea plants. Yellow (g) is recessive. What are the phenotypes of the following
allele pairs:
GG=
Gg=
gg=
3.
Tall is dominant to short. What would the genotype look like for a man who is homozygous for tall?
What are the possible gamete combinations (i.e. What alleles could the father donate)?
4.
What would the genotype look like for a woman who is heterozygous for tall?
What are the possible gametes (i.e. What alleles could the mother donate)?
5.
If the male and female in numbers 3 and 4 were to have a child, what are the possible genotypic and phenotypic ratios?
Show the punnett square.
6.
A family has four daughters. What is the probability that a fifth child could be a female? Show the punnett square.
7.
Use a punnett square to determine the possible genotypes of the F1 generation when a heterozygous black (Bb) rabbit is
crossed with a homozygous brown (bb) rabbit.
8.
White (W) hair is dominant over black (w) hair in sheep. A white male and a black female sheep are parents of a black
lamb. What is the probability that their next lamb will be white? Show the punnett square.
9.
The offspring of two short-tailed cats have a 25 % chance of having no tail, a 25% chance of having a long tail and a 50%
chance of having a short tail. What can you hypothesize based on this information about the genotypes of the parents.
10. What gamete combinations are possible when the following groups of alleles separate in meiosis?
AABB
AABb
AaBb
Aabb
11. What is a polygenic trait? Give two examples.
12. 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, is 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. Show the cross if two adults were heterozygous for both traits (EeGg).
a.
EeGg x EeGg Diagram the cross:
b. What are the chances of having a
child that is completely normal?
_________________________
c. What are the chances of having a
child that has just PKU?
_________________________
d. What are the chances of having a
child that has just galactosemia?
_________________________
e. What are the chances of having a
child that has both diseases?
_________________________
13. The diagram shows the possible allele combinations for
two traits when the sperm of an AaBb father is crossed
with the eggs of an AaBb mother. What is the
genotype of the zygote that is produced when the Ab
sperm is crossed with the AB egg? Fill in the entire
table.
AB
Ab
aB
AB
?
AB
Ab
AB
14. A tall pea plant sprouts up in a garden away from the
rest of the pea plants. You want to know if the pea
plant is heterozygous (hybrid) or homozygous
dominant (purebred). Explain how you would be able
to differentiate between a heterozygous and a
homozygous dominant individual with the same
phenotype (pg 183).
aB
S
Short-haired fur
s
Long-haired fur
ab
15. In snapdragons, flower color is controlled by incomplete dominance. The two alleles
are red (R) and white (W). The heterozygous genotype is expressed as pink.
a. What is the phenotype of a plant with the genotype RR? ___________
b. What is the phenotype of a plant with the genotype WW? ___________
c. What is the phenotype of a plant with the genotype RW? ___________
A pink-flowered plant is crossed with a white-flowered plant. What is the probability
of producing a pink-flowered plant? _________%
16. A homozygous red horse is mated with a roan horse (codominant = red and white hairs). What is the possibility of
producing another roan horse?
ab
17. Human blood types are determined by genes that follow the CODOMINANCE pattern of inheritance. There are two
dominant alleles (IA and IB) and one recessive allele (iO). Write the genotype for each person based on the description:
Homozygous for the “B” allele______
Type O ______
Heterozygous for the “A” allele______
Type “A” and had a type “O” parent______
Type “AB” ______
18. Two parents think their baby was switched at the hospital. Its 1968, so DNA fingerprinting technology does not exist yet.
The mother has blood type “O,” the father has blood type “AB,” and the baby has blood type “B.”
Mother’s genotype: _________
Father’s genotype: _________
Baby’s genotype: ________ or _________
Was the baby switched? Use a Punnett square showing all possible genotypes for children produced by this couple.
19. In mice, there is a lethal mutation that causes embryos with the homozygous dominant genotype YY to die before birth. Baby mice
with the genotype YG appear yellow, and GG mice are gray.
If two gray parent mice mate, what % of their offspring would be expected to die before birth?
20. In codominance, an organism that has both alleles of a gene displays both phenotypes at the same time. For example, a
cross between a black cat and a tan cat results in a tabby cat.
A tabby cat (BT) is crossed with a black cat (BB)
What is the pattern of inheritance in this example?
What is the genotypic ratio?
What is the phenotypic ratio?
21. A normal male (XHY) and a female (XHXH) who is a carrier of hemophilia marry. What is the probability of a child produced
by these two individuals would be born with the disease? Is this autosomal or sex-linked?
22. A man that is red-green colorblind (XnY) has a child with a woman (XNXN) that does not carry the colorblind gene. What is
the probability of a child produced by these two individuals is colorblind? Is this autosomal or sex-linked?
23. Eye color is a sex-linked trait in drosophilia. Red eyes are dominant over white eyes. Use a punnett square to determine
the possible genotypes and phenotypes of a cross between a white-eyed female and a red-eyed male.
24. Cystic fibrosis is an autosomal recessive disorder. If two phenotypically normal parents have a child with cystic fibrosis,
what are the genotypes of the two parents, and the child?
25. ______ If a human baby boy inherits a recessive allele from his mother, in which circumstance would he most likely show
the trait coded for by the recessive allele?
A. The baby inherits the dominant allele from his father
B. The allele is on the X chromosome.
C. The allele is on an autosomal chromosome and the baby is a twin D. The allele is on the Y chromosome.