Biology

Human Genetics and Disorders

844 Questions

Human Genetics and Disorders covers the inheritance patterns, genetic mutations, and molecular basis of hereditary diseases. Topics include sex-linked traits, cancer genetics, and metabolic disorders. This section tests knowledge critical for biology exams and general science papers.

Genetic mutationsInherited disordersCancer geneticsGenetic testingMendelian inheritance

Human Genetics and Disorders Questions

Multiple choice

Which of the following is a major problem in uncovering the genetic basis of autism in terms of the conventional approach?

Directions: Answer the question based on the following passage.

Autism has a strong genetic component: With one identical twin autistic, the other has a 70 percent chance of having it, a risk 10 times that of fraternal twins. Yet great, unsuccessful effort has been spent looking for its genetics. To Wigler, the key lies in spontaneous mutations - novel alterations in the parental germ line of the offspring. Last year he formed a controversial theory for it. It suggests that females, who develop autism with a 1/4th frequency with which males do, may carry the genetic profile for it.

Wigler attributes the failure of conventional studies to their studies on families with more than one autistic child to search for differences in one genetic base. These differences could be any alteration in a base called SNPs.  Uncovering SNPs shared by affected people would uncover high-risk people. The problem is locating the same target: they have implicated loci on 20 of the 23 human chromosomal pairs.

In his first autistic research, Wigler, with Sebat, tried to determine the role of spontaneous mutations, called copy number variations. Before human genome sequencing, researchers thought an individual always had two copies of a gene. In 2004, the team showed that even in healthy individuals, they could go missing from (or be added to) the genome via genetic rearrangements. Studies on families with only one autistic member showed that up to 10 percent of non-inherited autism cases could be caused by these rearrangements. They found that the structural events were primarily deletions, leaving individuals with only one copy of a particular gene and leading, sometimes, to its functional disruption.

Later, Wigler unveiled a unified genetic theory, which he cobbled together by examining families with multiple autistic individuals and incorporating both hereditary and spontaneous events. Focusing on families with the first two children affected, he found that third-born male children have a 50 percent risk of acquiring the disorder, whereas the risk for third-born girls is closer to 20 percent. From there, Wigler developed a two-tiered hypothesis: The majority fall into the low-risk category, having spontaneous mutation. Contrarily, high-risk families - 25 percent of all, manifest the disease when an unaffected individual, mostly female, carries a sporadic mutation. In case of a male, the chances are roughly half.

Although Wigler’s model is seen as a simpler way to view the genetics of autism, others find it incomplete. Critics note that it does not explain observations of families with an autistic child in which either second- or third-degree relatives are also affected or in which first-degree relatives show mild symptoms. And the model fails to explain why girls do not get autism as frequently as boys. Wigler believes that more data might help prove him. For instance, the girl-boy discrepancy could be explained if the genetic modifiers are sex-specific, an effect that might become apparent if researchers look at cases in which a normal mother has an autistic daughter.

  1. Too many chromosomes are responsible for it.

  2. There is great, complex interaction among different chromosomes responsible for autism, which is not amenable to studies.

  3. There is no clarity as to which chromosome is responsible for autism.

  4. Not enough subjects are available for studies.

  5. It is difficult to determine the role of spontaniety.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Options (1) and (2) run contrary to what is given in the passage. Thus, they are not justified. There is nothing said about the subjects available for study even, thereby ruling out option (4). Nor is spontaniety a consideration here. Refer to the last lines of paragraph 2 for the correct answer: “The problem is locating the same target: they have implicated loci on 20 of the 23 human chromosomal pairs.”

Multiple choice

Haemophilia is a

  1. Deficiency disease

  2. Chronic disease

  3. Acute disease

  4. Congenital disease
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Ans - 4

Multiple choice

Sickle cell anemia has not been eliminated from the African population because

  1. it is not a fatal disease

  2. it provides adaptiveness against malaria

  3. it is controlled by dominant genes

  4. it is controlled by recessive genes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Sickle cell trait provides a survival advantage against malaria in heterozygous individuals. This balanced polymorphism keeps the sickle cell gene in the population despite the lethality of the homozygous condition.

Multiple choice

Polydactyly in man is due to

  1. autosomal dominant gene

  2. autosomal recessive gene

  3. sex-linked dominant gene

  4. sex-linked recessive gene
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Polydactyly means having more than five digits in hand or feet. It is an abnormal hereditary trait which occurs due to dominant defective autosomal genes. 

Multiple choice

Hemophilia is caused by the absence of

  1. Factor IX

  2. Factor VIII

  3. Factor V

  4. Factor XII
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Hemophilia A is caused by a lack of the blood clotting factor VIII; about 9 out of 10 people with hemophilia have type A disease. This is also referred to as classic hemophilia or factor VIII deficiency.

Multiple choice

Which ONE of the following is NOT a cause of polycythaemia?

  1. Mutation of JAK 2

  2. Renal failure

  3. Congenital heart disease

  4. Haemoglobin abnormality

  5. Iron overload
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Iron overload is an excess iron in the body. Excess iron in vital organs, even in mild cases of iron overload, increases the risk for liver disease like cirrhosis, cancer , heart attack or heart failure, diabetes mellitus, etc.,  but it is not a cause of polycythaemia.

Multiple choice

In human, the ABO blood groups are determined by a multiple allelic system where IA and IB are co-dominant and dominant to IO. A newborn infant is type A, whose mother is type O. Possible phenotypes of the father are

  1. A, B or AB

  2. A, B or O

  3. O only

  4. A or AB
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Possible genotypes of the father are A or AB, as IA allele is required from one of the parent, as mother does not have IA allele, thus father should have IA allele.

Multiple choice

A husband and wife have normal vision but fathers of both of them were colourblind. Probability of their first daughter to be colour blind is

  1. 25%

  2. 50%

  3. 75%

  4. 0%
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A husband and wife have normal vision but father of both of them were colourblind. Probability of their first daughter to be colour blind is 0. Colour blindness is a sex linked recessively inherited disorder. Normal man has normal x and y chromosomes. Carrier female have one normal x and one abnormal x chromosome.The probability of their son to get colour blindness is 50%.

Multiple choice

Skin colour inheritance in man is

  1. monogenic

  2. polygenic

  3. sex-linked

  4. multiple allelic
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Skin colour inheritance in man is not monogenic, but it is polygenic, controlled by many genes like AABBCC, aabbcc, etc.

Multiple choice

Which of the following is a major problem in uncovering the genetic basis of autism in terms of the conventional approach?

PASSAGE – I

The passage is followed by a question based on its content. Answer the question on the basis of what is stated or implied in the passage.

Autism has a strong genetic component: With one identical twin autistic, the other has a 70 percent chance of having it, a risk 10 times that of fraternal twins. Yet great, unsuccessful effort has been spent looking for its genetics. To Wigler, the key lies in spontaneous mutations — novel alterations in the parental germ line of the offspring. Last year he formed a controversial theory for it. It suggests that females, who develop autism with a 1/ 4th frequency with which males do, may carry the genetic profile for it.

Wigler attributes the failure of conventional studies to their studies on families with more than one autistic child to search for differences in one genetic base. These differences could be any alteration in a base called SNPs.  Uncovering SNPs shared by affected people would uncover high-risk people. The problem is locating the same target: they have implicated loci on 20 of the 23 human chromosomal pairs.

In his first autistic research, Wigler, with Sebat, tried to determine the role of spontaneous mutations, called copy number variations. Before human genome sequencing, researchers thought an individual always had two copies of a gene. In 2004, the team showed that even in healthy individuals, they could go missing from (or be added to) the genome via genetic rearrangements.  Studies on families with only one autistic member showed that up to 10 percent of non-inherited autism cases could be caused by these rearrangements. They found that the structural events were primarily deletions, leaving individuals with only one copy of a particular gene and leading, sometimes, to its functional disruption.

Later, Wigler unveiled a unified genetic theory, which he cobbled together by examining families with multiple autistic individuals and incorporating both hereditary and spontaneous events. Focusing on families with the first two children affected, he found that third-born male children have a 50 percent risk of acquiring the disorder, whereas the risk for third-born girls is closer to 20 percent. From there, Wigler developed a two-tiered hypothesis: The majority fall into the low-risk category, having spontaneous mutation. Contrarily, high-risk families — 25 percent of all, manifest the disease when an unaffected individual, mostly female, carries a sporadic mutation. In case of a male, the chances are roughly half.

Although Wigler’s model is seen as a simpler way to view the genetics of autism, others find it incomplete. Critics note that it does not explain observations of families with an autistic child in which either second- or third-degree relatives are also affected or in which first-degree relatives show mild symptoms. And the model fails to explain why girls do not get autism as frequently as boys. Wigler believes that more data might help prove him. For instance, the girl-boy discrepancy could be explained if the genetic modifiers are sex-specific, an effect that might become apparent if researchers look at cases in which a normal mother has an autistic daughter.

  1. Too many chromosomes are responsible for it.

  2. There is great, complex interaction among different chromosomes responsible for autism, which is not amenable to studies.

  3. There is no clarity as to which chromosome is responsible for autism.

  4. Not enough subjects are available for studies.

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Options (1) and (2) run contrary to what is given in the passage. Thus, they are not justified. There is nothing said about the subjects available for study even, thereby ruling out option (4). Please refer to the last lines of paragraph 2 for the correct answer. The problem is locating the same target: they have implicated loci on 20 of the 23 human chromosomal pairs.