For an explanation, see the main splats page
SPLATS about reproduction
The principles of reproduction
- Sexual reproduction begins with a diploid zygote forming when nuclei from two haploid gametes fuse, but that only sets the scene for more complex development.
- Sexual reproduction provides for a more efficient mixing of genes in the offspring that result, giving them an advantage in terms of natural selection.
- Sexual reproduction requires a reduction division or meiosis to reduce the number of chromosomes before the gametes fuse and restore the total.
- The male part of a flower is the stamen, which contains the anthers that actually produce pollen grains. The ovary is located at the centre of most flowers.
- Asexual reproduction results in almost identical 'daughter' offspring being produced: this form is assumed to lead to slower evolutionary changes.
- Asexual reproduction provides quick and easy reproduction, especially in cases where it may be hard for one individual to find a mate or breeding partner.
- Many grasses and rosette plants spread by sending out runners into any vacant space and by trying to overgrow other plants, or to beat them to bare space.
- Higher plants reproduce in many ways, using seeds, cuttings, runners, and grafts, though some of these methods may be of more use than others.
- Self-pollination is a form of sexual reproduction, even though there is only one 'parent'. Most plants have mechanisms to favour 'outside' pollen.
- In many animals, the sex of offspring is determined by the presence or absence of a sex chromosome, but there are several variations on the basic plan.
- Pollen fertilizes a flowering plant when a pollen tube grows down, carrying a haploid nucleus to a point where that nucleus can fuse with one in the ovum.
- Pregnancy in human beings can be prevented or avoided by using different types of barriers to keep sperm cells away from ova, such as diaphragms and condoms.
- Pregnancy can be prevented by stopping women from ovulating (that is, producing ova). This is the way the more common forms of 'The Pill' operate.
- Pregnancy can be prevented by stopping men producing sperm cells, typically by means of a vasectomy, which prevents sperm cells entering the semen.
- Pregnancy in humans can be ended by abortion which may be caused either by natural conditions (spontaneous abortion), or mechanical or chemical interference.
- Pregnancy can be prevented by stopping or disrupting implantation of a fertilized ovum (some forms of 'Pill', including the 'morning-after' Pill).
- The health of a fetus may be checked by amniocentesis, which uses a needle to sample cells of the fetus that have been sloughed off into the amniotic fluid.
- In 1974, the first test-tube babies were conceived in vitro, after which they were implanted artificially, developed normally, and were born normally.
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