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Answer

Human is a diploid organism. Diploid means having two sets of chromosomes. There are 23 pairs of chromosomes out of which 22 pairs are autosome(a chromosome i.e, not sex chromosome) and 1 pair is sex chromosome. Human males are heterogamatic (xy) produce two types of gametes(sperms) x and y. Human females are homogametic, produce single type of gamete(egg) x. Sperms determine the sex of offspring (child). When a sperm carrying y chromosome fertilize with egg then a diploid zygote(xy) is produced leading to a male child. When a sperm carrying x chromosome fertilize with egg then a female child is produced.

In case of birds there are 76 pairs of autosomes and 1 pair of sex chromosome. Ovum determines the sex of the offspring. Female is heterogamatic (zw) whereas male is homogametic (zz). Here z chromosome is larger like x chromosome and w is smaller as compared to z chromosome.