Human Intervention in Evolution

Answering exam questions For each intervention ask yourself: How does it effect natural selection (are alleles being passed on that normally wouldn’t be? Are new alleles appearing in the population?)? How does it effect genetic variation (does it increase and therefore increase the chances of survival of a species with new selection pressures, or does it decrease)?

Selective Breeding Also called artificial selection Choosing which organisms breed together based on desirable traits Decreases genetic diversity (alleles for desired traits increase in frequency and alleles for non-chosen trait decrease in frequency in successive generations) Shortens time for development of desirable traits within organisms/species Maintains alleles (traits) in a gene pool that might not usually be retained (don’t contribute to survival or reproduction)

Examples of features maintained only by artificial selection can be seen in domesticated animals, such as: Jacobin pigeons, whose distinctive arrangement of neck feathers forms a ruff that masks their faces, except from immediately in front hairless cats and dogs English bulldogs, whose greatly shortened muzzles result in breathing problems

May lead to new species….

Artificial Insemination Artificially introducing gametes from a male with desired traits, into a female with desired traits Semen collected from male and injected into female reproductive tract Inserting sperm into a cow

Multiple Ovulation Administering hormones to mammals so they release multiple, mature ovaries instead of only 1 each cycle These eggs can be removed and fertilized, then the embryos inserted into surrogate mothers Increases the number of individuals with desired traits over a short period of time (compared with natural selection) Decreases frequency of undesired alleles

Artificial Pollination Humans pollinate plants with desired traits together Increase frequency of desired alleles Can also create new species by breeding together plants that would normally remain reproductively isolated

Cloning Asexual production of genetically identical organisms Decreases genetic diversity Cloned organisms are all equally as vulnerable to new selection pressures (therefore more susceptible to possible extinction)

Gene Transfer Between Species Introducing foreign genes into a species (transgenic organisms) Increase genetic diversity within a species May increase some organism’s chances of survival with particular selection pressures (therefore they survive to pass their alleles to successive generations, whereas normally they would not have)

Gene Therapy, Stem Cell Therapy Gene therapy introduces non-faulty genes into cells that have faulty copies of that gene Stem Cell therapy – replaces faulty cells with functional cells Both therapies increase the chances of the organism’s survival and therefore their ability to pass on alleles that may not have normally been passed onto future generations (e.g. the allele coding for the faulty gene in gene therapy patients will now continue in the population)

Genetic Screening Testing for genetic disorders in potential parents or in a pregnant woman before birth, by extracting DNA from the embryo (or the fluid surrounding the embryo) May result in decision not to have a child that would otherwise be born May result in decision not to reproduce Alleles not passed onto successive generations that might have been passed on otherwise (contraceptives have the same effect)

Collection of amniotic fluid with cells of embryo (and therefore it’s DNA)

Overcoming Infertility in Humans There are many different ways in which infertility can be overcome, in order to allow couples to conceive. Some examples are: Donor insemination(donor sperm used) IVF (multiple eggs fertilised and implanted) Donation of eggs (if woman can’t produce viable eggs of her own…uses partner’s sperm) Surrogacy (use surrogate mother’s uterus) Gamete intrafallopian transfer (increase chance of successful fertilisation)

Effects on evolution: All of these techniques result in pregnancies that may not normally occur This results in alleles being passed onto successive generations which may not have normally been passed on Some of these methods also result in allele combinations that might not normally have occurred