Gametes are specialised sex cells that fuse at fertilisation. They are haploid, containing a single set of chromosomes (23 in humans), so that fusion of a male and a female gamete gives a diploid zygote.In most organisms the two types of gamete are very different in size and behaviour:
• Male gametes are small, produced in very large numbers and able to travel to the female gamete. In animals the male gamete is the sperm (spermatozoon), which swims using a tail (flagellum). In flowering plants the male gametes are nuclei carried inside the pollen grain and delivered to the ovule by a pollen tube.
• Female gametes are larger, produced in smaller numbers and do not move. In animals the female gamete is the egg cell, or ovum, which contains food reserves in its cytoplasm for the early embryo. In flowering plants the female gamete is the egg cell inside the embryo sac of the ovule.
This difference makes sense: many small, mobile male gametes raise the chance that one reaches an egg, while a few large female gametes each provide the cytoplasm, organelles and nutrients the zygote needs.Because gametes are made by meiosis, each one carries a different combination of alleles. A human can produce 223, about 8.4 million, different combinations of chromosomes from independent assortment alone, before crossing over is even considered.The two gametes do not contribute equally in every way: almost all the mitochondria in the zygote come from the egg, so mitochondrial DNA is inherited from the mother.
• Male gametes are small, produced in very large numbers and able to travel to the female gamete. In animals the male gamete is the sperm (spermatozoon), which swims using a tail (flagellum). In flowering plants the male gametes are nuclei carried inside the pollen grain and delivered to the ovule by a pollen tube.
• Female gametes are larger, produced in smaller numbers and do not move. In animals the female gamete is the egg cell, or ovum, which contains food reserves in its cytoplasm for the early embryo. In flowering plants the female gamete is the egg cell inside the embryo sac of the ovule.
This difference makes sense: many small, mobile male gametes raise the chance that one reaches an egg, while a few large female gametes each provide the cytoplasm, organelles and nutrients the zygote needs.Because gametes are made by meiosis, each one carries a different combination of alleles. A human can produce 223, about 8.4 million, different combinations of chromosomes from independent assortment alone, before crossing over is even considered.The two gametes do not contribute equally in every way: almost all the mitochondria in the zygote come from the egg, so mitochondrial DNA is inherited from the mother.