3. Chapter 24 Medical Genetics

Fetus

Amniocentesis and karyotyping to detect chromosomal abnormalities

Which of the following characteristics of inheritance can be observed in the accompanying pedigree of a family affected by Tay-Sachs disease?

An affected offspring can have two unaffected parents. The trait occurs in both males and females. Affected individuals are offspring of heterozygous parents.

What is the inheritance pattern when a trait occurs with the same frequency in both sexes and an affected offspring can have two unaffected parents?

Autosomal recessive

Which type of mutation causes a dominant genetic disorder through the production of an altered protein that works against the action of the normal protein?

Dominant-negative

Which statement is true of X-linked dominant disorders such as Rett syndrome and Aicardi syndrome?

Males die at an early stage of development

Select human disorders inherited in an autosomal dominant fashion.

Marfan syndrome Aniridia Huntington disease

Which of the following characteristics of inheritance for hemophilia can be observed in the accompanying partial pedigree for the family of Queen Victoria and Prince Albert?

Mothers of affected males often have brothers with the disease. Males are more likely to be affected than females.

What tool do scientists use to follow a human pattern of inheritance from generation to generation?

Pedigree analysis

Which observations are consistent with a disease having a genetic basis? 2

Tay-Sachs disease can occur in 1/2500 births in a specific eastern European population while the frequency is 1/250,000 across Europe. A cancerous growth of immature nerve cells called neuroblastoma is associated with a deletion in a specific region of chromosome 11. The sleep disorder called narcolepsy has been related to an allele for a faulty neural receptor in dogs. Some humans also suffer from narcolepsy.

Adult

Test for carrier status if one belongs to a family with a history of a specific disease

Newborn baby

Test for excess phenylalanine demonstrating phenylketonuria (PKU)

Which of these is a common example of widespread genetic screening of newborns to identify certain disorders?

Test for excess phenylalanine indicating phenylketonuria (PKU)

Select observations that are consistent with a disease having a genetic basis.

The disease has a characteristic age of onset. Different populations tend to have different disease frequencies. The disease doesn't spread to individuals sharing similar environmental situations. A human disorder may resemble a disorder known to have a genetic basis in animals. There is a correlation between a human disease and a mutant gene or chromosomal alteration. Identical twins share the disease more often than non-identical twins. A person with a disease is more likely to have genetic relatives with the disease than are people in the general population.

In the accompanying pedigree, a filled symbol indicates an individual with Huntington disease while a clear symbol shows an unaffected individual. Which of the following characteristics of inheritance can be observed for this affected family?

The trait occurs in both males and females. An affected individual has at least one affected parent.

True or false: Identical twins share a genetic disease more often than fraternal twins.

True

Consider the accompanying partial pedigree showing inheritance of hemophilia in the family of Queen Victoria and Prince Albert. If Xh is the allele for hemophilia and XH is the allele for normal blood clotting, which genotypes are missing among the children of Alice of Hesse and her husband, in the middle of the figure?

X(^H) Y X(^H) X(^H)

What is the inheritance pattern for a trait that is more likely to occur in females when it is lethal to males?

X-linked dominant

What is the inheritance pattern for a trait that more commonly affects males than females and can often be observed in brothers or fathers of a woman who has affected sons?

X-linked recessive

Marfan syndrome, which is inherited in an autosomal dominant manner, is caused by a mutation in the gene for

fibrillin-1

A dominant genetic disorder can be caused by ______, a situation where one functional copy of an allele is not sufficient to produce a normal phenotype.

haploinsufficiency

Genetic testing is used to determine whether a(n) ______ has a disease-causing gene, while genetic screening is used to determine how frequently the gene is found in a(n) ______.

individual; population

Amniocentesis is a procedure for ______.

obtaining fetal cells in a sample from the fluid surrounding the fetus

A prion is a disease-causing agent made ______.

only of protein

When a human disease is caused by a mutation in a single gene, scientists follow the pattern of inheritance by analyzing charts called human

pedigrees

Monozygotic twins

share 100% of the same alleles

When a human disease is caused by a mutation in a single gene, the pattern of inheritance is called _____ Mendelian inheritance.

simple

When a defect in a single gene causes a human disease, the mutant gene often follows

simple Mendelian inheritance patterns

To study the distribution of disease-causing genes, genetic ______ refers to determining if an individual carries the faulty gene, while genetic ______ relates to assessing the presence of the gene throughout a population.

testing; screening

The autosomal recessive human disorder albinism (type I) is caused by a mutation in the gene for

tyrosinase

Select the human disorders that are inherited in an autosomal recessive fashion.

Cystic fibrosis Phenylketonuria Sickle cell disease

True or false: Comparing someone with a genetic disease to another person in the general population, the person with the disease is more likely to have a family member with the same disease.

True

What is the inheritance pattern for a trait that more commonly affects males than females and which will occur in about 50% of the sons born to the unaffected daughter of an affected male?

X-linked recessive

The disease hemophilia is caused by a deficiency in any one of three blood clotting factors. Two of these factors are encoded by genes on the X chromosome and the other clotting factor gene is located on an autosome. Since mutations in more than one gene can cause hemophilia, this represents ______.

locus heterogeneity

Simple Mendelian inheritance is a pattern observed when a human disorder is caused by ______.

mutation in a single gene (Reason: Simple Mendelian inheritance also applies to diseases caused by recessive alleles.) (Reason: Simple Mendelian inheritance also applies to diseases caused by dominant alleles.)

Chorionic villus sampling is a procedure for ______.

obtaining a sample of the fetal part of the placenta

Suppose a disease-causing allele shows autosomal recessive inheritance. How could a carrier of this disease-causing allele be identified?

Carriers often show reduced activity for the enzyme encoded by the allele.

True or false: Dizygotic twins share a genetic disease more frequently than monozygotic twins.

False

Approximately how many human diseases have a genetic basis?

Thousands

Twins that are genetically identical to each other are called ______ twins.

monozygotic

What is the inheritance pattern for a trait that occurs with equal frequency in both sexes and will be inherited, on average, by 50% of the offspring of an affected individual who had only one affected parent?

Autosomal dominant

What is the inheritance pattern for a trait that occurs with the same frequency in both sexes and two affected heterozygous individuals have, on average, 25% unaffected offspring?

Autosomal dominant

What is the inheritance pattern when the trait occurs with the same frequency in both sexes and two unaffected heterozygotes have, on average, 25% affected children?

Autosomal recessive

Which observations are consistent with a disease having a genetic basis?

One family in the neighborhood has one parent and several children with severe hearing loss. No one in any of the other nearby families has deafness. Nephroblastoma is a cancer of the kidney that typically develops in children and is only rarely found in adults. Someone with a diagnosis of retinitis pigmentosa has learned that there are family members in the preceding three generations who had the disease.

The abnormal form of a prion protein causes a neurodegenerative disease by ______.

catalyzing the conversion of the normal protein form to the abnormal form

Preimplantation genetic diagnosis is a method testing for genetic diseases in ______.

embryos produced by in vitro fertilization

In the accompanying pedigree, a filled symbol indicates an individual with Huntington disease while a clear symbol shows an unaffected individual. Considering the symbol for individual II-5, you conclude that her father, I-1 is ______ allele for Huntington disease.

heterozygous for the autosomal dominant

Embryos produced by in vitro fertilization can undergo genetic testing by ______.

preimplantation genetic diagnosis

Consider the children of II-6 and II-7 in the accompanying pedigree for a family affected by Tay-Sachs disease. What is one genotype that could have been produced by these two parents but was not observed?

Unaffected homozygote (Reason: A heterozygote would be unaffected by Tay-Sachs disease.) (Reason: 11-6 and 11-7 are unaffected heterozygotes.) (Reason: Only one parent carries the Tay-Sachs allele.)

Which type of catalytic activity occurs in prion-caused diseases?

The abnormal form of the prion protein catalyzes a reaction that converts normal proteins to misfolded ones.

Tay-Sachs disease is inherited with an autosomal recessive allele that leads to a defect in the enzyme hexosaminidase A. When cells are collected from patients, cells with different genotypes exhibit different amounts of enzymatic activity. Rank the amount of enzymatic activity that would be detected in a biochemical assay on cells from patients of these genotypes, with the genotype producing the LEAST amount of enzymatic activity on top.

homo r hetero homo d

The use of information about a patient's genotype in order to select a medication or therapy that is specifically suited to the patient is called

personalized medicine

Personalized medicine can be used to select a

therapy preventative measure medication