Genetics Part 2 Test Review
Codominance/Incomplete Dominance/Multiple Alleles/Polygenic Traits
1. What is Codominance? Give an example from the notes. _An organism will express both alleles for a trait
because they are both dominant. An example is how a chicken can have both black and white
feathers.________________________________________________________________________ ____
2. What is incomplete dominance? Give an example from the notes. _Both alleles are relatively weak and
neither is totally dominant to the other. A blending occurs in the offspring. An example of this is flower colors
(Blue and red parent flowers can make purple – think paint mixing)._________________________
3. Blood typing is a common example of codominance. Show a Punnett Square with a parent who has AA
blood and a parent who has BO blood.
4. In the Punnett Square above, what are the TWO dominant alleles? What is the recessive allele? ___A and B
are dominant alleles. O is a recessive allele.________________________________________
5. In the notes we looked at Snapdragons. Show a Punnett Square for a heterozygous (pink) snapdragon
crossed with a recessive (white snapdragon).
6. In the Punnett Square above, what percent of the offspring are white? What percent are pink? What is the
phenotypic ratio? _ White – 50%, Pink – 50%. Ratio – 2:2________________________________
7. What is the definition of the term multiple alleles? Give an example from the notes. ___There are more
than two alleles for a certain trait. Blood typing in humans is an example (and yes, it’s also an example of
codominance)._______________________
8. What is the definition of polygenic inheritance? Give an example from the notes. ___Multiple genes
influence the phenotype. Examples are height and skin color______________________________
9. When examining blood types, how many phenotypes do we find? (circle one)
2
3
4
Genetics Part 2 Test Review
Sex-Linked Traits
1. A sex-linked trait is usually found on which chromosome (circle one)
X
Y
2. Why do certain conditions have a higher incidence (more individuals have the condition) in males?
__Because the trait is carried on the X chromosome and males only have one X
chromosome.________________________________________________________________________
3. If a female is homozygous for a sex-linked trait, what will happen to her male offspring? __The males will
definitely have the trait._________________________________________________________
4. Colorblindness is a sex-linked trait. Show a Punnett Square for a mom that is heterozygous for colorblindness and a dad who is colorblind.
5. What percentage of their male children will be colorblind? ______50%_________________________
Karyotypes
1. What is a karyotype? __Pictures that show chromosomes in homologous pairs._______________
2. Why is a karyotype important? __It can show information about a fetus being healthy or having genetic
abnormalities._________________________________________________________
3. How can you see a Trisomy disorder on a karyotype? ___If there are three chromosomes present on any of
the pairs a child has a trisomy disorder (example: trisomy 18 is three chromosomes on what should be the
18th pair)________________________________________________________
Pedigrees
1. What is a pedigree? ___A chart that shows the occurrence of a certain trait in a
family.___________________________________________________________________
2. Why is a pedigree useful? __So people can see how traits move through generations.____________
3. What does a square represent in a pedigree? __A male ____________________________________
4. What does a circle represent in a pedigree? ___A female__________________________________
5. What does a shaded shape represent? ____An affected individual______________________________
Genetics Part 2 Test Review
Genetic Disorders
1. What is nondisjunction? __Homologous chromosomes fail to separate during meiosis.________
2. What can nondisjunction result in? __Incorrect numbers of chromosomes________________
3. Give an example of nondisjunction. ____Trisomy 21____________________________________
4. Could nondisjunction be identified on a karyotype? ___Yes__________
5. Where do genetic disorders occur? __In the chromosomes of an organism______________________
FLASHBACK SECTION:
Dihybrid Crosses/Gene Expression/Meiosis
Use the dihybrid cross below to answer the questions.
R = round, r = wrinkled, Y = yellow, y = green
RrYy x RRyy
1. What is the probability of an offspring being round? _____100%______________________
2. What is the probability of an offspring being yellow? _____0%______________________
3. What is the phenotypic ratio in this dihybrid? _____8:8______________________
Genetics Part 2 Test Review
4. What would the phenotypic ratio be if the cross was RrYy x RrYy? __9:3:3:1_____________________
5. Can the environment influence how genes are expressed? __YES. Temperature, light, and chemicals are all
examples of things that can influence gene expression in the environment.____________________________
6. What percentage of genes comes from mom? _______50% (EVEN IF A CHILD LOOKS MORE LIKE ONE
PARENT)________________
7. What percentage of genes comes from dad? ________50%_______________
8. Are the cells made in meiosis haploid or diploid? __haploid____________________
9. How do we note that? (circle one)
2n
n