Week 4 Chapter 22: Medical Genetics

what causes cancer?

1. Gene mutations (such as oncogenes and tumor suppressors) 2. Environment 3. Viruses 4. Environmental agents/ chemical 5. Chemicals (e.g., from smoking), radiation, viruses, and heredity all contribute to the development of cancer by triggering changes in a cell's genes 5. Chemicals and radiation act by damaging genes, viruses introduce their own genes into cells, and heredity passes on alterations in genes that make a person more susceptible to cancer

key characteristics of cancer

1. Most cancers originate in a single cell 2. Cancer is usually a multi-step process that begins when a precancerous genetic change (benign growth) progresses to cancer cell growth. 3. An environmental agent that causes cancer is called a carcinogen such as the harmful chemicals in cigarettes that can cause lung cancer

list the seven observations that suggest a disease may have a genetic component

1. When an individual exhibits a disease, this disorder is most likely to occur in genetic relatives than in the general population 2. Identical twins (monozygotic twins) share the disease more often than non-identical (dizygotic) twins 3. The disease does not spread to individuals sharing similar environmental situations 4. Different populations tend to have different frequencies of the disease 5. The disease tends to develop at a characteristic age. This is also called the age of onset 6. The human disorder may resemble a disorder that is already known to have a genetic basis and an animal 7. A correlation is observed between a disease and a mutant human gene or chromosomal aberration

Colorblindness is an X-linked recessive trait. A phenotypically normal man and a colorblind woman have two sons. What is the probability that both of them are color blind? Assume no new mutations.

1/1

Hemophilia is an X-linked recessive trait. A heterozygous female is married to a phenotypically normal male. What percentage of their offspring is expected to have hemophilia?

50% of the sons, and 0% of the daughters

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

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

Which of the following accurately describes the genetic change(s) leading to malignancy?

A series of successive gene changes occurs, involving oncogene activation and inactivation of tumor-suppressor genes.

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

Autosomal recessive

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

What is the most common mode of transmission for genetic disorders involving defective enzymes?

Autosomal recessive inheritance

In what disease do genetic changes lead to uncontrolled cell growth?

Cancer

oncogenes

Cancer-causing Gene, promotes cell division genes whose PRESENCE in certain forms and/ or overactivity can stimulate the development of cancer

Which change from proto-oncogene to oncogene occurred by chromosomal translocation?

Creation of a new transcription factor through the fusion of chromosomal segments from two different chromosomes

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

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

Which type of growth has cells that can invade other tissues and migrate to other areas of the body to form secondary tumors?

Malignant growth

medical genetics

Medical genetics involves the application of genetics to medical care, including research on the causes and inheritance of genetic disorders, and their diagnosis and management Medical geneticists specialize in medicine that involves the interaction between genes and health. They are trained to evaluate, diagnose, manage, treat, and counsel individuals of all ages with hereditary disorders.

What 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. Someone with a diagnosis of retinitis pigmentosa has learned that there are family members in the preceding three generations who had the disease. Nephroblastoma is a cancer of the kidney that typically develops in children and is only rarely found in adults.

Which outcome is consistent with the genetic change that occurs when a cell loses both members of a homologous chromosome pair?

The loss of tumor-suppressor genes on these chromosomes causes the cell to grow uncontrollably.

Suppose a translocation occurs so that a portion of one chromosome is joined to another non-homologous chromosome. Which situation would cause the cell to grow uncontrollably as a result?

The sequence arrangement in the newly-fused chromosome leads to overactive expression of a proto-oncogene.

Cancer cells may carry gain-of-function mutations that increase the activity of an oncogene. In what ways could the expression of the protein encoded by the oncogene be altered by this type of mutation?

The structure of the protein is altered so that it is overly active. The amount of protein produced from the oncogene is significantly increased. The protein is expressed in a cell type where it is not normally found.

Cancer can result from inactivation of which type of gene?

Tumor-suppressor gene

Which of the following features are characteristic of autosomal recessive inheritance?

Two affected individuals must have affected children. The trait occurs in the same frequency in both males and females. An affected offspring can have two unaffected parents.

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

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

Hemophilia A is a(n) ______ disorder caused by a defect in the ______.

X-linked recessive ; clotting factor VIII

Consider the accompanying 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, what is the one possible genotype that is missing among the children of Beatrice and her husband, at the right of the figure?

XHXH

A benign tumor is

a localized growth with a precancerous genetic change.

A carcinogen is

an environmental agent that causes cancer.

During the initial stage of cancer development, cells with a precancerous genetic change form a(n)

benign growth

A malignant tumor

can invade nearby healthy tissue. can form secondary tumors after spreading to other locations. has cells with cancerous mutations leading to uncontrolled growth.

Chemicals in the environment that cause cancer are called

carcinogens.

Ewing's sarcoma is a cancer of the bone and soft tissues where a new transcription factor is produced from the fusion of the coding regions of two different proteins. The ews gene of chromosome 22 is joined to the fli1 gene of chromosome 11. Neither the ews nor the fli1 gene individually causes cancer. This change from proto-oncogene to oncogene occurred as a result of

chromosomal translocation.

Most cancer cells are descendants of an original cell that acquired genetic changes. Therefore, cancerous growths are considered to be ______ in origin.

clonal

Hemophilia A, or classical hemophilia, is an X-linked recessive disorder caused by a defect in the gene that encodes the protein ___ ___ VIII

clotting factor

In cancer biology, transformation is the process of

converting a normal cell into a malignant cell.

The tumor-suppressor gene p53 has a significant role in

detecting DNA damage in a cell.

tumor suppressor genes

encode proteins whose normal activities inhibits cell division normal genes whose ABSENCE can lead to cancer.

True or false: Genetic disorders that are caused by defective enzymes are typically inherited in an autosomal dominant fashion.

false

An oncogene is typically formed by a _______ mutation in a normal gene called a(n) _______

gain-of-function ; proto-oncogene

The ERBB2 receptor normally plays a role in promoting cell division. Cells from many breast cancer patients show an increase in the number of ERBB2 receptors available on the plasma membrane. The type of mutation that contributed to cancer development in these cases would be called a ______-of-function mutation in a(n) ______

gain; oncogene

A cancer cell is a cell that

has accumulated genetic changes that allow it to grow uncontrollably.

A cancer-causing change occurs when a tumor-suppressor gene is

inactivated

A series of genetic changes, involving oncogene activation and tumor-suppressor gene inactivation, leads to

malignancy.

The ability of cancer cells to migrate to other parts of the body where they can cause secondary tumors is referred to as

metastasis.

Cancer cells can migrate to other parts of the body and cause secondary tumors. This property is called

metastatic

If a disorder has a genetic component, a pair of monozygotic twins is

more likely to exhibit the disorder than are dizygotic twins.

An oncogene is formed when a proto-oncogene gains a

mutation that causes its expression to be abnormally active.

A mutant gene that is over-expressed and contributes to the formation of cancer is termed a(n)

oncogene

A gene that promotes cancer is called a(n)

oncogene.

Cancerous growths are clonal in origin because cancer cells

originate from a single cell that has accumulated genetic changes during cell division.

Which gene plays a significant role in detecting DNA damage in a cell?

p53

A tumor-suppressor gene codes for a protein that normally

prevents cancerous growth.

For chronic myelogenous leukemia, a chromosomal translocation leads to

production of a BCR/ABL fusion protein that promotes division of white blood cells.

A normal, nonmutated gene that has the potential to become an oncogene is called a(n) ___ -oncogene.

proto

A normal gene that when mutated becomes an oncogene is called a(n)

proto-oncogene.

Suppose a cell gains an extra copy of one chromosome. Overactive expression of ______ on that chromosome and its related homologues can cause the cell to ______.

proto-oncogenes; grow uncontrollably

Cancer cells may carry gain-of-function mutations that increase the activity of an oncogene. In which of the following ways could the expression of the protein encoded by the oncogene be altered by this type of mutation?

the structure of the protein is altered so that it is overly active. The protein is expressed in a cell type where it is not normally found. The amount of protein produced from the oncogene is significantly increased.

The process of converting a normal cell into a malignant cancer cell is called

transformation

Chronic myelogenous leukemia is due to production and overexpression of a BCR/ABL fusion protein caused by

translocation of the portion of chromosome 9 carrying the abl gene to the area of chromosome 22 with the bcr gene

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

true

A gene that codes for a protein that prevents cancerous growth is a(n)

tumor-suppressor gene.