Gametogenesis

Gametogenesis

Male
1. produce spermatogonia (2n), these divide through several generations by mitosis.
2. Spermatogenesis involves production of sperm & requires meiosis
3. each spermatocyte undergoing meiosis produces 4 haploid (n) sperm cells
4. growth phase takes place prior to meiosis in the formation of the spermatocyte & differentiation into sperm takes place after production of 4 haploid spermatids
Female
1. numerous diploid oogonia grow & differentiate prior to meiosis to produce diploid primary oocyte
2. products of meiosis I are a haploid secondary oocyte & a haploid polar body (cannot be fertilised).
3. Fertilisation of oocyte results in primary oocyte finishing meiosis II producing a 2nd polar body & a fertilised diploid egg cell
4. egg cell very large, contains cytoplasm and mitochondria required by early embryo
Summary
1. Spermatogenesis partitions cytoplasm equally & produces 4 haploid sperm cells
2. Oogenesis accumulates cytoplasm in one egg cell & packages other haploid sets of genetic material into polar bodies
3. Cytoplasm contributes to zygote development following fertilisation
Genetic Imprinting
1. Humans cannot survive with two paternal or two maternal contributions one set of chromosomes from each
2. means we inherit only one working copy of some genes. Either copy from mum or the copy from dad is epgienetically silenced.
3. Silencing usually happens through the addition of methyl groups during egg or sperm formation
4. Also, some genes are only active when inherited from a female, others when inherited from the male - complex process that occurs in gametogenesis

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