Modern Genetics Study Guide
Concepts to Know
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In DNA fingerprinting, a person’s DNA is cut into fragments, which are separated to form a
pattern.
The process of selecting a few organisms with desired traits to serve as parents of the next
generation is called selective breeding.
Cystic fibrosis is a genetic disorder in which the body produces abnormally thick mucus.
Sex-linked recessive traits are more common in males.
Three or more forms of gene that code for a single trait are called multiple alleles.
Inserting working copies of a gene directly into the cells of a person with a genetic disorder is
referred to as gene therapy.
A clone is an organism that is genetically identical to the organism from which it was produced.
In hybridization, breeders cross two genetically different individuals.
The goal of the genetic counselors has been to identify the DNA sequence of every human gene.
A (n) genome is all the DNA in one cell of an organism.
People with an extra copy of chromosome 21 have a disorder called down syndrome.
An abnormal condition that a person inherits through genes or chromosomes is a genetic
disorder.
In a pedigree, a square is used to represent a male.
The sex chromosomes determine if a person is a male or female.
A chart that tracks which members of a family have a particular trait is called a pedigree.
The transfer of genes from one organism to another is called genetic engineering.
The crossing of two individuals that have similar characteristics is referred to as inbreeding.
A genetic disorder in which a person’s blood clots very slowly if at all is hemophilia.
A person who has one recessive and one dominant allele for a trait is called a carrier.
An example of a human trait that is controlled by more than one gene is skin color.
Study about pedigree pgs.153 in your book
Essay
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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.
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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.
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.
Smile dimples are controlled by a dominate 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 simple dimples? Draw a Punnett square to show how you arrived at your
answer.
o The chance is 50 percent. Smile dimples are a dominant trait, so Alberto and Pedro both
have the dd genotype. Therefore, Whitney must be Dd, and 50 percent of the children
of a Dd x dd cross should have smile dimples.
Although all Janele’s hemoglobin 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 with 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 percent of the children should be normal (SS), 50 percent 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 Students should draw a Punnett square showing an IAIB x ii cross, with possible
offspring genotypes of IAi and IBi. From this, students should conclude that Janice could
have either type A blood or type B blood.