Biology [2 Mark Question Answer]

 

IDENTICAL TWINS	FRATERNAL TWINS
They are formed when a single fertilised egg   splits      and produces two individuals.	They are formed when two different eggs are fertilised   by      two different sperms.
They are exactly the same.	They are like normal brother or sisters.
They are of the same sex.	They may be of same sex or different.
They have similar genotype and phenotype.	They have different genotype and phenotype.

(i) Ovulation is the release of a mature egg from the ovary.
(ii) Fertilisation of the egg usually occurs in the fallopian tube.

Emerging from the warm and safe environment of the mother's womb, the new-born baby heralds its survival into the external world with a full-throated cry.
Cry is critical for its survival. It sweeps the first breath of air into the lungs of the baby, which until the moment of birth remain inactive and collapsed.

The ovum released by the ovary is swept into the uterine tube by the ciliary action of the fimbriae. The further movement of ovum along the oviduct is by:
• Ciliary action of the epithelium.
• Fluid currents in the oviduct.
• Peristaltic contraction of muscles of oviduct.

Gametes are reproductive cells which differ from other body cells is that they contain haploid (one half) chromosome number.
During spermatogenesis and oogenesis, the germ cells undergo meiosis in which the chromosome number is reduced to half, i.e., each cell (sperm or ovum) now has 23 chromosomes instead of 46 .