A child is born with an extra chromosome in each of its cells. This condition is usually the result of

A) Nondisjunction

B) Crossing over

C) Segregation

D) Hybridization

Correct Answer: Option A – Nondisjunction

Nondisjunction is the result of the paired homologous chromosomes separating unequally during meiosis. So instead of one of a particular chromosome going to each of the D resulting sex cells, one cell gets two chromosomes of that type. Then during fertilization that zygote gets three of that particular chromosome instead of the normal two, resulting in one extra chromosome. That zygote then undergoes mitosis, resulting in all the cells of that organism containing one extra chromosome.Hence, option A is the correct answer.

Crossing over of chromosomes occurs during the formation of gametes, but this iss not responsible for an additional chromosome in a cell.Hence, option B is incorrect.

Segeregation is separation of the replicated chromosomes to form B new cells – this occurs in asexual reproduction.Hence, option C is incorrect.

Hybridization is the process of combining B different varieties of organisms to produce a hybrid organism.

Hence, option D is incorrect.

Mutations can be considered as one of the ingredients of evolution since, they

A) Are beneficial to the organisms in which they appear

B) Contribute to variations in organisms

C) Cause the extinction of an organism

D) Are related to the environment in which they occur

Correct Answer: Option B – contribute to variations in organisms

Mutations usually happen randomly and lead to increase in variety of organisms. This variety in the organisms helps them to survive in the changing environment, hence, leading to evolution.

Hence, option B is the correct answer.

Mutations are beneficial since they support evolution. But this statement does not provide the reason why mutations are beneficial. Hence, option A is incorrect.

Mutations do not cause the extinction of an organism and are not related to the environment in which they occur.

Hence, options C and D are incorrect.

Which combination represents the combination of a homozygous condition?

A) Bb

B) bb

C) Ab

D) Cb

Correct Answer: Option B – bb

Humans possess 2 genes for every trait that are located on homologous chromosomes. 1 homozygous genotype means that an individual has the same genes for a particular trait on the homologous chromosomes. We represent genes as letters and for any one trait we must use the same letter, a capital letter meaning the dominant gene while a lower case letter meaning a recessive gene.

Hence, option B with the combination bb is the correct answer.

Answers A, C and D are incorrect since they have a combination of a dominant gene denoted by a capital letter and a recessive gene denoted by small letter.

The presence of DNA is important for cellular metabolic activities because:

A) It directs the production of enzymes

B) It directly increases the solubility of nutrients

C) It is a major component of the cytoplasm

D) It is a structural component of the cell wall

Correct Answer: Option A – It directs the production of enzymes

DNA directs the production of enzymes and these enzymes in turn guide the metabolic activities of the cell.

Hence, option A is the correct answer.

DNA does not increase the solubility of the nutrients; it is neither the major component of the cytoplasm nor the structural component of the cell wall.

Hence, options B, C and D are incorrect.

Which statement best explains the significance of meiosis in the process of evolution within a species?

A) Gametes produced by meiosis ensure continuation of any particular species by asexual reproduction.

B) Equal number of eggs and sperms are produced by meiosis

C) Meiosis produces similar eggs and sperms

D) Meiosis provides for variation in the gametes produced by an organism

Correct Answer: Option D – Meiosis provides for variation in the gametes produced by an organism

When meiosis occurs, random variations in the gametes formed lead to the changes that help survival of organisms and their evolution. Hence, option D is the correct answer.

Gametes do not help in asexual reproduction.

Hence, option A is incorrect.

Meiosis does not ensure equal number or similar eggs and sperm cells.

Hence, options B and C are incorrect.

Which hormone regulates the sexual reproductive cycles of the human males?

A) Testosterone

B) Estrogen

C) Progesterone

D) Insulin

Correct Answer: Option A – Testosterone

Testosterone is hormone produced in the testes of human males. This hormone regulates the sexual cycle of the human males.

Hence, option A is the correct answer.

Estrogen and progesterone are produced by the ovaries and are responsible for the regulation of the sexual cycle of the human females.

Hence, options B and C are incorrect.

Insulin is produced by the pancreas and it regulates the blood sugar level in humans.

Hence, option D is incorrect.

Removing the nucleus from the body cell of one organism and placing it in an egg cell which had its nucleus removed, leading to the production of an organism which is genetically alike is known as:

A) Fertilization

B) Cloning

C) DNA production

D) Biological adaptation

Correct Answer: Option B – cloning

Cloning involves production of B organisms which are genetically alike by inserting the nucleus of the body cell of an organism to be cloned into an egg cell and then growing this egg cell.

Hence, option B is the correct answer.

Fertilization is the union of B gametes to form a zygote which grows into an organism.

Hence, option A is incorrect.

Biological adaptations occur naturally in the process of evolution. And DNA is not produced but exists in the nucleus of cells.

Hence, options C and D are incorrect.

Body cells of a fruit fly contain 8 chromosomes. In some cells there are only D chromosomes. This condition in a fruit fly occurs due to:

A) Mitosis

B) Meiotic cell division

C) Embryonic differentiation

D) Fertilization

Correct Answer: Option B – Meiotic cell division

Meiotic cell division leads to haploid cells containing half the number of chromosomes of the parent cell.

Hence, option B is the correct answer.

Mitosis leads to the formation of daughter cells with the same number of chromosomes as the parent cell.

Hence, option A is incorrect.

Embryonic differentiation refers to the process by which specialized structures arise during the development of an embryo.

Hence, option C is incorrect.

Fertilization is the process of union of B gametes to form a zygote. This does not lead to reduction in the number of chromosomes in a cell.

Hence, option D is incorrect.

Heavy cigarette smoking during pregnancy increases the likelihood of:

A) Birth of twins

B) Birth of male baby

C) Baby being born with viral infection

D) Baby being born with medical problems

Correct Answer: Option – D – baby being born with medical problems

Cigarettes have chemicals which can lead to medical complications in the new born baby.

Hence, option D is the correct answer.

Cigarette smoking during pregnancy does not lead to the birth of twins or a male baby, since these occur by the combination of gametes and cannot be guided by cigarettes.

Hence, options A and B are incorrect.

Viral infections generally occur once the baby is born and cigarette smoking during pregnancy is not a reason for this condition.

Hence, option C is incorrect.

Name one of the early steps in the formation of both egg and sperm cells

A) Yolk accumulation

B) Chromosome pairing

C) Polar body formation

D) Unequal division of cytoplasm

Correct Answer: Option B – Chromosome pairing

Both egg and sperm cells are formed by the process of meiosis. In the early stages of meiosis chromosome pairing occurs.

Hence, option B is correct.

After pairing of chromosomes, polar body formation occurs. Hence, option C is not the earliest step in the process of formation of sperm and egg cells.

Hence, option C is incorrect.

Yolk is the fertilized part of an egg.

Hence, option A is incorrect.

Cytoplasm is divided equally after the nucleus divides into B daughter nuclei.

Hence, option D is incorrect.