All Free Biology MCQs with Answers

• A. Deletion
• B. Point mutation
• C. Insertion
• D. Aberration

Explanation: The change in the number of chromosomes, either an increase or a decrease from the normal diploid number, is referred to as chromosomal aberration.

• A. Chemicals
• B. Radiations
• C. Water
• D. None of the above

Explanation: Water is not considered a mutagen. Mutagens are agents that can induce mutations in DNA, potentially leading to changes in the genetic material of an organism. Examples of mutagens include certain chemicals, radiation (such as UV radiation or X-rays), and some biological agents.

• A. Insertion
• B. Point mutation
• C. Deletion
• D. Transposition

Explanation: Sickle cell anemia is indeed caused by a point mutation in the gene that codes for the beta-globin subunit of hemoglobin. This point mutation results in the substitution of a single nucleotide in the DNA sequence, leading to the replacement of a glutamic acid residue with a valine residue in the resulting protein.

• A. Sickle cell anemia
• B. Diabetes
• C. Phenylketonuria
• D. None of the above

Explanation: Phenylketonuria is a genetic disorder caused by a mutation in the gene responsible for producing the enzyme phenylalanine hydroxylase (PAH). This enzyme is crucial for the breakdown of the amino acid phenylalanine. When PAH is deficient or nonfunctional, phenylalanine levels in the blood can become elevated, leading to various symptoms, including intellectual disability (formerly referred to as mental retardation), seizures, behavioral problems, and other neurological issues if left untreated.

• A. Genes are present on DNA
• B. Genes are present on chromatids
• C. Genes are present on chromosomes
• D. All of the above

Explanation: The chromosomal theory of inheritance suggests that genes, the units of heredity, are located on chromosomes. This theory proposes that chromosomes, which contain DNA and associated proteins, carry the genetic information that determines an organism's traits. It also explains how traits are passed from parents to offspring during the process of cell division, such as during meiosis and mitosis.

• A. There are more chromosomes but less gene
• B. There are more gene but less chromosomes
• C. Each chromosome carry only one gene
• D. None of the above

Explanation: The objection was: If Mendelian characters are determined by genes located on the chromosomes, and if the independent assortment of Mendelian traits reflects the independent assortment of chromosomes in meiosis, why does the number of characters that assort independently in a given kind of organism often greatly exceed the number of chromosome pairs the organism possesses?

• A. All the male were red eyed
• B. All the female were white eyed
• C. Neither of female white eyed
• D. All of the above

Explanation: The strange result observed by T.H. Morgan during his experiments with fruit flies (Drosophila melanogaster) was the absence of any female flies with white eyes. In his experiments, Morgan observed that while male fruit flies with white eyes (a recessive trait) could be produced, no female fruit flies with white eyes were observed, despite the fact that according to Mendelian genetics, both males and females should inherit traits in a similar manner.

• A. Transforming activity continues after destruction of protein
• B. Transforming activity continues after destruction of lipids
• C. Transforming activity continues after destruction of DNA
• D. Transforming activity continues after destruction of carbohydrates

Explanation: In the experiments conducted by Avery, MacLeod, and McCarty in 1944, they demonstrated that when DNA was destroyed using enzymes that specifically targeted DNA (DNase), the transforming activity responsible for converting non-virulent bacteria into virulent ones ceased. This provided strong evidence that DNA, rather than protein or RNA, was the substance responsible for carrying genetic information. Therefore, the correct statement should be that transforming activity ceases after destruction of DNA.

• A. DNA is double helix
• B. Base paring is purine and pyrimidine
• C. DNA is composed of parallel strands
• D. Base pair are plainer

Explanation: Explanation for this question will be added soon!

• A. Both strands are synthesized
• B. None of the strands is synthesized
• C. Only one strand is synthesized
• D. None of the above

Explanation: Explanation for this question will be added soon!