Heredity Study Guide – ANSWER KEY
1. Define the following terms:
a. Autosomes: Chromosomes 1-22 that hold genetic information for self
b. Sex chromosomes: chromosomes X & Y that code for sex of individual
c. Sex-linked trait: genes that are only in the X or Y chromosomes
d. Sex influenced trait: traits that are influenced by hormones in the body
e. Pedigree: diagram that shows how a trait in inherited over generations
f. Mutation: a change in a sequence of a gene, can be beneficial or harmful
g. Nondisjunction: type of disorder when a chromosome fails to split
during meiosis and sex cells a different in number
2. What are some examples of linked genes?
Some examples of linked genes would be hair and eye color, hair color and
freckles, and pea color and pod shape.
3. What can you learn from a chromosome map?
A chromosomal map can determine where a gene is including which
chromosomes a disorder is found on.
4. What is a karyotype used for? How many chromosomes are in a normal karyotype?
A karyotype is used to determine the sex of an individual and whether or not
there is a chromosomal disorder. There are 46 chromosomes in a normal
karyotype.
5. Be able to read and analyze a pedigree.
a. What symbol represents female? circles
b. What symbol represents male? squares
c. What does it mean if a symbol is colored in? the person will exhibit that
trait and express it
d. What do horizontal lines between symbols represent? A marriage or if
there were offspring between the couple
e. How many children do parents 5 & 6 have? 3 children, 2 girls and 1 boy
6.
7. Analyze the following karyotypes. Determine the sex of the individual and if there is
a chromosomal disorder.
Sex: male
Chromosomal disorder? no
If yes, which chromosome?
Sex: female
Chromosomal disorder? no
If yes, which chromosome?
Sex: female
Chromosomal disorder? yes
If yes, which chromosome? 1 X
Sex: female
Chromosomal disorder? yes
If yes, which chromosome? 3 #21
Sex: female
Chromosomal disorder? yes
If yes, which chromosome? 3 #13
Sex: female
Chromosomal disorder? yes
If yes, which chromosome? 3 #18
8. Explain why males determine the sex of their offspring in humans.
Males can create sperm cells that can offer either an X or Y chromosome.
Females can only offer an X chromosome. Depending on whether an X or Y
sperm cell fertilizes an egg cell will determine if the child is a boy or girl. If XX
then it will be a girl. If XY then it will be a boy.
9. Use the karyotype above to answer the following question. The individual above is a
suspect in a crime and new evidence shows that from DNA analysis the killer is a
carrier for an X-linked disorder known as Duchenne muscular dystrophy. Could this
individual possibly be a carrier for Duchenne muscular dystrophy? Name the
genetic disorder that is individual has that could allow a male to be a carrier for an
X-linked trait and whether they would be considered innocent of the crime.
Yes, it is possible for this person to be a carrier for Hemophilia because they
have 2 X chromosomes and therefore can be a carrier if one is affected. This
person has Klinefelter’s syndrome, which is XXY syndrome. They are males
but have an extra X chromosome.
10. In humans, colorblindness is a recessive, sex-linked trait. What is the probability
that the children of a woman heterozygous for colorblindness and a man with
normal color vision will be colorblind? Explain your answer.
The probability that the child of a woman that is heterozygous for
colorblindness and a man with normal vision is 25%. This child will be a male.
There is a 25% chance they will have a female that is a carrier.
X
XC
X
XX
XXC
Y
XY
XCY