Question 1

Why do carriers for sickle cell anemia have a genetic advantage in some situations over those who are not carriers?

Accepted Answer

Carriers of the sickle cell trait have a single copy of the sickle cell gene and a normal hemoglobin gene, which provides them with a selective advantage in malaria-endemic regions. The altered shape of red blood cells in carriers makes it harder for the malaria parasite to infect and survive in these cells, thus offering increased resistance to malaria.

Question 2

Figure 10-5 
-Which genetic condition is revealed in the karyotype display in Figure 10-5?

Accepted Answer

Down syndrome is characterized by an extra copy of chromosome 21, which would be visible in a karyotype as three copies of chromosome 21 instead of the usual two.

Question 3

Suppose you are a genetic counsellor, and a man and woman come to you with concerns that if they have a child together, it could have cystic fibrosis. Also suppose that genetic tests reveal that the woman is a carrier for cystic fibrosis but the man is NOT. Which of the following is the best advice you could give them?

Accepted Answer

Cystic fibrosis is an autosomal recessive disorder, meaning that a child must inherit two copies of the faulty gene (one from each parent) to develop the condition. If one parent is a carrier (has one copy of the faulty gene) and the other parent is not (has no copies of the faulty gene), their children cannot inherit two copies of the faulty gene and therefore cannot develop cystic fibrosis. However, each child has a 50% chance of inheriting the single faulty gene from the carrier parent, making them a carrier as well.

Question 4

Suppose that you are a genetic counsellor, and a couple comes to you with concerns that if they have a child together, it could have hemophilia. Suppose also that neither one of them has hemophilia, but the woman's biological father did have an X-linked recessive form of hemophilia. Which of the following is the best advice you could give them?

Accepted Answer

Hemophilia is an X-linked recessive condition. Since the woman's father had hemophilia, she must have one affected X chromosome (making her a carrier) because she inherited an X chromosome from her father. The man cannot pass an X chromosome to his sons (only Y chromosomes), so sons have a 50% chance of inheriting the affected X from their mother and having hemophilia. Daughters receive one X from their mother and one from their father, so they will not have hemophilia (since it requires two affected X chromosomes for a female to express the condition) but have a 50% chance of being carriers like their mother.

Question 5

A mutation in the human gene for a fibroblast growth factor receptor (FGFR) is related to cartilage formation. Which disorder does this mutation appear to be responsible for?

Accepted Answer

Achondroplasia is a disorder of bone growth that causes the most common type of dwarfism. It is indeed associated with mutations in the fibroblast growth factor receptor 3 (FGFR3) gene, which affects cartilage formation.

Question 6

Prenatal diagnosis techniques such as amniocentesis and chorionic villus sampling involve the removal of cells that were produced by an embryo. What are these cells then used for?

Accepted Answer

These cells are used to test for genetic disorders or chromosomal abnormalities in the fetus, such as Down syndrome or cystic fibrosis, by analyzing the DNA from the collected cells.

Question 7

Which genes are subject to cytoplasmic inheritance?

Accepted Answer

Genes found in mitochondria and chloroplasts are subject to cytoplasmic inheritance because these organelles have their own DNA and are inherited through the cytoplasm, usually from the mother.

Question 8

Most hospitals routinely test all newborns for an autosomal recessive disorder in which an enzyme in amino acid metabolism is NOT produced. In this disorder, lack of the enzyme leads to a buildup of compounds that damage brain tissue, possibly leading to mental retardation, unless a restricted diet is followed. What is the name of this disorder?

Accepted Answer

The disorder described is phenylketonuria (PKU), an autosomal recessive metabolic disorder characterized by the deficiency of the enzyme phenylalanine hydroxylase. This deficiency leads to a buildup of phenylalanine, which can cause brain damage and mental retardation if not managed with a strict diet.

Question 9

How does the age of the mother seem to correlate with the incidence of genetic birth defects?

Accepted Answer

The incidence of genetic birth defects tends to increase with the age of the mother. This is particularly noted with conditions such as Down syndrome, where the risk increases significantly as maternal age rises, especially after age 35.

Question 10

About 10% to 15% of African Americans are carriers of an autosomal recessive genetic disorder in which a defective version of hemoglobin is produced. What is the name of this disorder?

Accepted Answer

Sickle cell anemia is the disorder characterized by the production of a defective form of hemoglobin, which leads to the sickle shape of red blood cells. This condition is particularly prevalent among African Americans, with about 10% to 15% being carriers of the sickle cell trait.

Question 11

About 4% of people of northern European descent are carriers for an autosomal recessive genetic disorder in which a defective membrane transport protein leads to abnormal chloride levels in extracellular fluids. What is the name of this disorder?

Accepted Answer

Cystic fibrosis is characterized by a defective membrane transport protein that affects chloride levels in extracellular fluids, common among people of northern European descent.

Question 12

Which of the following is most likely to happen to a human polyploid?

Accepted Answer

Polyploidy, the condition of having more than two complete sets of chromosomes, is often incompatible with life in humans. It frequently results in natural abortion (miscarriage) because the genetic abnormalities are too severe for the embryo to develop properly.

Question 13

Which of the following occurs in cells of human individuals with three or more X chromosomes?

Accepted Answer

In human cells, regardless of the total number of X chromosomes, only one X chromosome remains active in each cell. The additional X chromosomes are inactivated through a process called X-chromosome inactivation (XCI), ensuring that the cells have a normal dosage of X-linked genes. This process is crucial for the development and function of cells in individuals with more than one X chromosome, such as those with conditions like Triple X syndrome.

Question 14

Suppose you are a genetic counsellor, and a man and woman come to you with concerns that if they have a child together, it could have hemophilia. Also suppose that the woman has an X-linked recessive form of hemophilia, but the man does NOT. Which of the following is the best advice you could give them?

Accepted Answer

Hemophilia is an X-linked recessive condition. Since the mother has hemophilia, she has two affected X chromosomes (XX). The father, who does not have hemophilia, has a normal X and a Y chromosome. Male offspring receive an X chromosome from their mother and a Y chromosome from their father, meaning all male offspring will inherit the affected X from the mother and thus have hemophilia. Female offspring receive one X chromosome from each parent, so they will inherit one affected X from the mother and one normal X from the father, making them carriers but not affected by the condition.

Question 15

A woman with which of the following human conditions would exhibit normal physical features?

Accepted Answer

Triple-X syndrome, also known as 47,XXX, is a condition where a woman has an extra X chromosome. Most women with this condition have normal physical features and may not even know they have it unless they undergo genetic testing for other reasons.

Question 16

Suppose that you are a genetic counsellor, and a man and woman come to you with concerns that if they have a child together, it could have sickle cell anemia. Also suppose that genetic tests reveal that the man and woman are both carriers for sickle cell anemia. Which of the following is the best advice you could give them?

Accepted Answer

Sickle cell anemia is inherited in an autosomal recessive manner. When both parents are carriers (heterozygous for the sickle cell allele), their children have a 25% chance of inheriting two sickle cell alleles (one from each parent) and having sickle cell anemia, a 50% chance of being carriers like their parents (inheriting one sickle cell allele and one normal allele), and a 25% chance of inheriting two normal alleles.

Question 17

Which of these disorders has X-linked recessive inheritance?

Accepted Answer

Duchenne muscular dystrophy is an example of an X-linked recessive disorder, meaning it is linked to the X chromosome and typically manifests in males who have only one X chromosome.

Question 18

Suppose you are a genetic counsellor, and a man and woman come to you with concerns that if they have a child together, it could have hemophilia. Also suppose that the man has an X-linked recessive form of hemophilia, but the woman does NOT, and that genetic tests reveal the woman is NOT a carrier for hemophilia. Which of the following is the best advice you could give them?

Accepted Answer

Since the father has the X-linked recessive form of hemophilia and the mother does not carry the gene for hemophilia, all of their daughters will receive one X chromosome with the hemophilia gene from their father and one normal X chromosome from their mother, making them carriers. Their sons will receive the Y chromosome from their father and a normal X chromosome from their mother, so they will not have hemophilia.

Question 19

About half of all flowering plant species, including many important crop plants, belong to which category of chromosomes?

Accepted Answer

Polyploids have multiple sets of chromosomes, which is a characteristic of about half of all flowering plants, including many important crop species. This genetic trait can lead to greater variability and sometimes increased vigor or size, which are beneficial for agricultural purposes.

Question 20

Which autosomal dominant genetic trait associated with a gene on human chromosome 4 leads to a type of dwarfing due to defective cartilage formation?

Accepted Answer

Achondroplasia is an autosomal dominant genetic disorder caused by a mutation in the FGFR3 gene on chromosome 4, leading to defective cartilage formation and a type of dwarfism.

Quiz 10: Genetic Linkage, Sex-Linkage, and Other Non-Mendelian Inheritance Mechanisms