PCB 3063 Exam 2 Review
Chapter 24: Medical Genetics
1. Be able to explain why it is important to understand genes and the interaction of genes
with the environment both for normal health and disease. Be able to explain that under
healthy conditions, genes encode proteins that play important roles and perform
important functions to maintain normal cellular processes. Mutations in genes (leading to
loss of function, gain of function, etc) may lead to diseased states.
● PKA
2. Be familiar with the seven characteristics that are associated with diseases that have a
genetic basis. Given a list of statements, pick the statement/statements that support or do
not support genetic disease.
● An individual who exhibits a disease is more likely to have genetic relatives with
the disorder than is someone in the general population.
● Identical twins share the disease more often than nonidentical twins.
○ Monozygotic (MZ) twins are genetically identical to each other because
they were formed from the same sperm and egg.
○ Dizygotic (DZ) twins, aka as fraternal or nonidentical twins, are formed
from separate pairs of sperm and egg cells.
○ Fraternal twins share, on average, 50% of their genetic material.
○ Concordance: the degree to which a trait or disorder is inherited,
determined by how many pairs of twins both exhibit it.
● The disease does not spread to individuals sharing similar environmental
situations.
● Different populations tend to have different frequencies of the disease.
● The disease tends to develop at a characteristic age.
● The human disorder may resemble a disorder that is already known to have a
genetic basis in an animal.
● A correlation is observed between a disease and a mutant human gene or a
chromosomal alteration.
○ We may be able to identify the altered genes or chromosomes that occur
only in people exhibiting the disorder to see if the disease has a genetic
basis.
3. Define concordance and what are the theoretical values for different types of disorders
(assuming certain parental genotypes)
, ● Concordance: the degree to which a trait or disorder is inherited, determined by
how many pairs of twins both exhibit it.
● For diseases caused by a single gene, concordance among identical twins should
be 100%. For fraternal twins, concordance for dominant disorders is
expected to be 50%, assuming only one parent is heterozygous for the disease.
For recessive diseases, concordance among fraternal twins is expected to be
25% if we assume both parents are heterozygous for the disease.
4. Be able to explain factors that make the study of inheritance of human diseases difficult.
How is inheritance of genetic disease best studied currently?
● Controlled matings are not possible.
● Sibship sizes are relatively small.
● Complete penetrance is sometimes lacking (the symptoms associated with the
disorder are not always produced). Penetrance refers to the proportion of people
with a particular genetic variant (or gene mutation) who exhibit signs and
symptoms of a genetic disorder.
● Degrees of expressivity sometimes vary.
Inheritance of genetic disease is best studied through pedigrees. These are diagrams
that show the relationship among members of a family, as well as their status with
respect to a particular hereditary condition.
5. Be able to list the five major inheritance patterns of traits or diseases controlled by single
genes. Be able to list examples of each as given in the in book (need not worry about
specific gene names or chromosomal locations)
● Autosomal dominant
○ Trait usually present in every generation
○ Members of both sexes affected equally
○ Unaffected parents produce unaffected offspring
○ Two affected parents can produce unaffected offspring
○ On average, half the children of an affected parent will be affected
○ The homozygous for the disease-causing allele is generally more severely
affected than the heterozygote
○ Examples:
, ● Autosomal recessive
○ Trait tends to skip generations
○ Members of both sexes affected equally
○ Unaffected parents can have an affected child
○ Two affected parents cannot have an unaffected child
○ Traits are more likely to occur in consanguineous marriages
○ Examples:
Chapter 24: Medical Genetics
1. Be able to explain why it is important to understand genes and the interaction of genes
with the environment both for normal health and disease. Be able to explain that under
healthy conditions, genes encode proteins that play important roles and perform
important functions to maintain normal cellular processes. Mutations in genes (leading to
loss of function, gain of function, etc) may lead to diseased states.
● PKA
2. Be familiar with the seven characteristics that are associated with diseases that have a
genetic basis. Given a list of statements, pick the statement/statements that support or do
not support genetic disease.
● An individual who exhibits a disease is more likely to have genetic relatives with
the disorder than is someone in the general population.
● Identical twins share the disease more often than nonidentical twins.
○ Monozygotic (MZ) twins are genetically identical to each other because
they were formed from the same sperm and egg.
○ Dizygotic (DZ) twins, aka as fraternal or nonidentical twins, are formed
from separate pairs of sperm and egg cells.
○ Fraternal twins share, on average, 50% of their genetic material.
○ Concordance: the degree to which a trait or disorder is inherited,
determined by how many pairs of twins both exhibit it.
● The disease does not spread to individuals sharing similar environmental
situations.
● Different populations tend to have different frequencies of the disease.
● The disease tends to develop at a characteristic age.
● The human disorder may resemble a disorder that is already known to have a
genetic basis in an animal.
● A correlation is observed between a disease and a mutant human gene or a
chromosomal alteration.
○ We may be able to identify the altered genes or chromosomes that occur
only in people exhibiting the disorder to see if the disease has a genetic
basis.
3. Define concordance and what are the theoretical values for different types of disorders
(assuming certain parental genotypes)
, ● Concordance: the degree to which a trait or disorder is inherited, determined by
how many pairs of twins both exhibit it.
● For diseases caused by a single gene, concordance among identical twins should
be 100%. For fraternal twins, concordance for dominant disorders is
expected to be 50%, assuming only one parent is heterozygous for the disease.
For recessive diseases, concordance among fraternal twins is expected to be
25% if we assume both parents are heterozygous for the disease.
4. Be able to explain factors that make the study of inheritance of human diseases difficult.
How is inheritance of genetic disease best studied currently?
● Controlled matings are not possible.
● Sibship sizes are relatively small.
● Complete penetrance is sometimes lacking (the symptoms associated with the
disorder are not always produced). Penetrance refers to the proportion of people
with a particular genetic variant (or gene mutation) who exhibit signs and
symptoms of a genetic disorder.
● Degrees of expressivity sometimes vary.
Inheritance of genetic disease is best studied through pedigrees. These are diagrams
that show the relationship among members of a family, as well as their status with
respect to a particular hereditary condition.
5. Be able to list the five major inheritance patterns of traits or diseases controlled by single
genes. Be able to list examples of each as given in the in book (need not worry about
specific gene names or chromosomal locations)
● Autosomal dominant
○ Trait usually present in every generation
○ Members of both sexes affected equally
○ Unaffected parents produce unaffected offspring
○ Two affected parents can produce unaffected offspring
○ On average, half the children of an affected parent will be affected
○ The homozygous for the disease-causing allele is generally more severely
affected than the heterozygote
○ Examples:
, ● Autosomal recessive
○ Trait tends to skip generations
○ Members of both sexes affected equally
○ Unaffected parents can have an affected child
○ Two affected parents cannot have an unaffected child
○ Traits are more likely to occur in consanguineous marriages
○ Examples:
