The sperm and the egg make different contributions to zygote. Which of the following statements about their contributions are true? (i) Sperm contributes most of the mitochondria. (ii) Egg contributes most of the cytoplasm. (iii) Both sperm and egg contribute haploid nucleus. (iv) Both sperm and egg contribute centrioles.

Question

The sperm and the egg make different contributions to zygote. Which of the following statements about their contributions are true? (i) Sperm contributes most of the mitochondria. (ii) Egg contributes most of the cytoplasm. (iii) Both sperm and egg contribute haploid nucleus. (iv) Both sperm and egg contribute centrioles. (A) (i) and (ii) (B) (ii) and (iii) (C) (iii) and (iv) (D) (i), (ii), (iii) and (iv)

Tardigrade Admin · Accepted Answer

The sperm is composed of different parts, namely, the head, neck, a middle piece, and the tail. The head of the sperm contains a haploid elongated nucleus which carries DNA (genetic material). The anterior portion of the sperm head is covered by a cap-like structure called the acrosome. It is filled with digestive enzymes that help in the lysis of the egg membrane during penetration. On the other hand, the secondary oocyte, which was arrested at the metaphase stage during ovulation, completes the second meiotic division when the sperm enters the cytoplasm of the egg cell. This gives rise to a haploid ovum and a second polar body, which fuses with the sperm cell to produce a diploid zygote.
Since the secondary oocyte retains a bulk of the nutrient-rich cytoplasm of the primary oocyte, the ovum formed is larger in size as compared to the sperm, and therefore, it contributes most of the cytoplasm during fertilisation. The sperm cell consists of very limited cytoplasm.
Due to its size, the egg cell also contributes to most of the mitochondria to the zygote. However, the centrioles are contributed solely by the sperm cell, as it consists of two types of centrioles in the neck region - proximal and distal.