Sexual Redroduction: Sperm and Ova structures, meiosis and life cycles

Edited by Jamie (ScienceAid Editor), SpellBot, Taylor (ScienceAid Editor)

Sexual reproduction is a way of producing offspring where the DNA of two parents mix to make a genetically different offspring (this is what mammals do). This is opposite to asexual reproduction where clones are made, like with bacteria.

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A gamete is the scientific term for sex cells that contain the DNA that is going to be passed on to the offspring. Males and females have different gametes, and here we will look at the human sperm and ovum.

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human gametes: the ovum and sperm
  1. 1
    Some key parts of the ovum are the yolk droplets in the cytoplasm that provide energy to the developing fetus until it connects to the mother by the umbilical chord. And the polar body is the other half of the ovum produced because it doesn't divide evenly.
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  2. 2
    Key parts of the sperm cell include: acrosome that contains enzymes that break down the jelly coat so it can enter. And the middle piece contains a lot of mitochondria that provide energy for the tail to flick about to move it.
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Now we've looked at differences in the structures, we'll look at some other key differences.

Ovum Sperm
Size Over 100μm in diameter. About 25μm long
Number produced Relatively few and aren't replenished. Trillions produced in a lifetime, and 400 million per ejaculate, constantly being developed.
Mobility The ovum gets moved along the Fallopian tube by cillia. The sperm move themselves with the tail.


For more about meioisis see: Variation and Meiosis.

We won't go into too much detail about this process. But it's similar to [biology/cell/cycle.html|mitosis], in that it goes from a diploid cell to a haploid by dividing so that a cell with pairs of homologous chromosomes divides. Each new cell has one chromosome from each homologous pair. Meiosis is important because it produces haploid gametes so when the two fuse, the resulting zygote has got a diploid number of chromosomes. This is maintained from generation to generation.

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Life Cycle

A life cycle shows how haploid (n) and diploid (2n) vary over time.

life cycle of organism

The life cycle of the above organism may seem a bit odd, but the only rules you need to remember are that meiosis halves the chromosome number but mitosis maintains it. And that fertilization doubles the number; and you should have no problem.

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Categories : Genetics

Recent edits by: SpellBot, Jamie (ScienceAid Editor)

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