All Free Biology MCQs with Answers

• A. 93
• B. 330
• C. 331
• D. 993

Explanation: Codon consists of three nucleotides, and each codon corresponds to a single amino acid. A stop codon, however, does NOT code for an amino acid; they signal the end or termination of the polypeptide chain. Hence, out of the 993 nucleotides, the last three correspond to a stop codon and hence 990 nucleotides are to be considered. 990 nucleotides correspond to 330 codons (990 divided by 3), and since each codon codes for a single amino acid, 330 codons will code for 330 amino acids, hence, the answer is B.

• A. Dispersive idea
• B. Conservative idea
• C. Disruptive idea
• D. Semi-conservative idea

Explanation: It is 'dispersive replication', which involves each daughter strand containing both parental and new DNA, as the old DNA is broken up and randomly dispersed into each daughter strand.

• A. Nucleus
• B. Chromosome
• C. Chromatin body
• D. Chromatid

Explanation: In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.

• A. Alzheimer's disease
• B. Parkinson's disease
• C. Anemia
• D. Hemolytic anemia

Explanation: Mutations probably include a combination of age-related changes in the brain along with genetic, environmental, and lifestyle factors. Parkinson's disease is caused by a loss of nerve cells in the part of the brain called the substantia nigra. Dietary deficiency-lack of iron, vitamin B12, or folic acid in the diet-causes anemia.

• A. 34 nanometer
• B. 3.4 Angstrom
• C. 3.4 nanometer
• D. 34 micrometers

Explanation: At a distance of 3.4nm, the double helix DNA produces one full turn. Each full turn of DNA consists of 10 base pairs. Pitch is the term for the distance covered by a DNA molecule in one full turn.

• A. Uracil, Cytosine and Thymine
• B. Cytosine, Guanine and Uracil
• C. Adenine and Guanine
• D. Cytosine, Adenine and Thymine

Explanation: The pyrimidines, Thymine, Cytosine and Uracil, are smaller and have a single ring, while the purines, Adenine and Guanine, are larger and have two rings.

• A. 2
• B. 4
• C. 6
• D. 8

Explanation: Humans have 2 pairs of chromosomes. So for each pair, there are two options available. 2C1 x 2C1= 2 x 2 = 4 When two pairs of chromosomes undergo meiosis, the different combinations of maternal and paternal chromosomes lead to four different types of gametes. This is due to the independent assortment of homologous chromosomes during meiosis I. Each homologous pair aligns independently during metaphase I, leading to a random distribution of maternal and paternal chromosomes into the resulting gametes. As a result, four different combinations of alleles are possible for each pair of chromosomes.

• A. Homozygous
• B. X chromosomes
• C. Y chromosomes
• D. Heterozygous

Explanation: Correct option is D. Humans have two sets of chromosomes. Homozygous and heterozygous are terms that are used to describe allele pairs. Individual organisms bearing different alleles (Rr) are known as heterozygous.

• A. Migration
• B. Mutation
• C. Genetic drift
• D. Selection

Explanation: Random mutations are the ultimate source of genetic variation. Mutations are likely to be rare and most mutations are neutral or deleterious, but in some cases, the new alleles can be favoured by natural selection.

• A. Polymorphic
• B. Heteromorphic
• C. Homomorphic
• D. Automorphic

Explanation: The 23rd pair in man is heteromorphic and defines the gender of the person.