Ch 5 Genetic Disorders Study Guide
Concepts to Know





















An example of a human trait that is controlled by more than one gene is skin color
A person who has one recessive and one dominant allele for a trait is called a carrier
A genetic disorder in which a person’s blood clots very slowly if at all is hemophilia
The crossing of two individuals that have similar characteristics is referred to as inbreeding
The transfer of genes from one organism to another is called genetic engineering
A chart that tracks which members of a family have a particular trait is called a pedigree
The sex chromosomes determine if a person is a male or female
In a pedigree, a square is used to represent a male
An abnormal condition that a person inherits through genes or chromosomes is a genetic
disorder
People with an extra copy of chromosome 21 have a disorder called Down syndrome
A genome is all the DNA in one cell of an organism
Professionals who help couples understand their chances of having a child with a particular
genetic disorder are called genetic counselor
In hybridization, breeders cross two genetically different individuals
A clone is an organism that is genetically identical to the organism from which it was produced
Inserting working copies of a gene directly into the cells of a person with a genetic disorder is
referred to as gene therapy
Three or more forms of a gene that code for a single trait are called multiple alleles
Sex-linked recessive traits are more common in males
Cystic fibrosis is a genetic disorder in which the body produces abnormally thick mucus
The process of selecting few organisms with desired traits to serve as parents of the next
generation is called selective breeding
In DNA fingerprinting, a person’s DNA is cut into fragments, which are separated to form a
pattern
Smile dimples are controlled by a dominant allele on a single gene. Whitney has smile dimples
but her husband Alberto and son Pedro do not. What is the chance that Whitney and Alberto’s
next child will have smile dimples? Draw a Punnett square to show how you arrived at your
answer.
o The chance is 50%. Smile dimples are a dominant trait, so Alberto and Pedro both have
the dd genotype. Therefore, Whitney much be Dd, and 50% of the children of a Dd x dd
cross should have smile dimples
D
d
D
d
DD
Dd
Dd
dd
D


Although Janele’s blood is normal, her brother Randy has sickle-cell disease. Janele is worried
about having a child with the disease. Janele just found out that her husband Terence has one
allele for sickle-cell disease. As their genetic counselor, determine Janele and Terence’s
chances of having a child with sickle-cell disease. How would you explain the results of your
analysis to the couple?
o Janele and Terence have a zero percent chance of having a child which sickle-cell
disease. Janele is normal, so she has the SS genotype. Terence has sickle-cell trait, so he
is Ss. In an SS x Ss cross 50% of the children should be normal (SS), 50% should have one
allele for sickle-cell disease (Ss), and none could have sickle-cell disease (ss)
Janice’s mother has type AB blood, and her father has type O blood. What blood type (s) could
Janice have? Draw a Punnett square to explain your answer.
o





You need to draw a Punnett square showing an IAIB x ii cross, with possible offspring
genotypes’ of IAi and IBi. From this, you should know that Janice could have either type
A blood or type B blood.
IA
IB
ii
IAii
IBii
ii
IAii
IBii
What is cystic fibrosis, and what causes it?
o Cystic fibrosis is a genetic disorder in which the body produces abnormally thick mucus
in the lungs and intestines. It is caused by a recessive allele. The recessive allele is the
result of a mutation in which three bases have been removed from a DNA molecule
What useful information does DNA fingerprinting provide?
o DNA fingerprinting technology can be used to identify people and show whether people
are related
Why can a karyotype detect Down syndrome but not hemophilia?
o Down syndrome is caused by an extra copy of a chromosome, so it can be detected in a
karyotype, which is a picture of all the chromosomes in a cell. Hemophilia is caused by a
recessive gene on the X chromosome, which appears normal in a karyotype
Explain how bacteria can be genetically engineered to produce a human protein such as
insulin.
o Plasmids are removed from bacterial cells. Enzymes cut open the plasmid and also
remove the human gene from its chromosome. The human gene attaches to the open
ends of the plasmid. After some bacteria take in the plasmid, they begin to produce the
human protein
Why can’t a male be a carrier of colorblindness?
o A male cannot be a carrier of colorblindness because it is a sex-linked trait. Males have
only one X chromosome and therefore only one allele for the trait. A carrier is someone
with one normal allele and one allele for the trait
Make sure you understand what a Pedigree is and how to read one.