Human Interventi

on in Evolution

Advantages of Artificial Selection

• Specific individuals selected to contribute to next generation for:– Economic reasons– Aesthetic reasons

Reproductive Technologies

• Artificial insemination• Multiple ovulations and embryo transfer

(MOET)• Sex selection through sperm sorting• Oestrus synchronisation

Artificial Insemination

• Via artificial insemination one ejaculate can fertilise 10 females.

• Semen can be snap frozen in liquid nitrogen and stored for many years

• Semen is collected from male and transferred to females• Advantage is yield: normally in a single mating there is the

potential for one female to be inseminated

Artificial Insemination

Advantages• Can fertilize many

females• Can fertilize distant

females• Can fertilize beyond the

lifespan of the male• Prized male can make

larger genetic contribution

Disadvantages• Loss of genetic diversity• As one allele is

favoured, alternatives are completely lost

• Whilst breeding for a particular trait, others may be unintentionally gained or lost

Artificial Insemination in plants

• Cover stigma• Remove stamen• Collect pollen

from anthers• Expose to stigma

of many other plants

Artificial Insemination in plants

• When one species is used to fertilize another, a hybrid is produced

• As chromosomes are non-homologous, hybrid is sterile

• Treatment with certain chemicals will cause doubling of chromosomes in all cells, thereby producing a fertile hybrid

Wheat(Triticum)

WW

x Rye(Secale)

RR

Sterile hybridWR

Fertile hybrid(Triticosecale)

WWRR

Treatment with

colchicine

Multiple ovulations and embryo transfer (MOET)

• Valued females can also make a larger genetic contribution.1. Inject with FSH (stimulates super-ovulation)2. Inject with GnRH (all eggs mature

simultaneously)3. Fertilise eggs through in-vitro fertilisation4. Implant eggs in to surrogate female

• MOET will usually increase the yield of a valued female by a factor of 7

Sex selection through sperm sorting

1. Add a harmless fluorescent dye to sperm2. Dye attaches to DNA3. X chromosomes contain more DNA4. Sperm containing X chromosome will

fluoresce more brightly5. Select these sperm

Oestrus synchronisation

• All females in herd are effectively “put on the pill” by being given progesterone.

• If all are taken of progesterone at the same time, ovulation will occur simultaneously.

• Makes herd easier to manage

Cloning

• Technique #1 – Embryo splitting– Pryor to blastocyst formation (>32 cells), the cells

of the zygote can be divided with a very fine needle and implanted in to a surrogate.

• Technique # 2 – Nuclear transfer– Can be performed via somatic cell fusion– Can be performed via fusion with a donor embryo

cell

Somatic cell fusionFusion with a donor embryo

Dolly was created via nuclear transfer (somatic cell fusion)

Some cloning successes

CC Snuppy with the “mother” from which she was

cloned

Snuppy with her surrogate mother

The downside to cloning

• Many unsuccessful attempts– CC (cat): 87– Snuppy (dog): 123– 2nd Chance (bull): 189– Dolly (sheep): 277

• This does not apply to plants as cloning occurs naturally– (cuttings, runners,

rhizomes)

• Shortening telomeres– Every time a cell divides

it loses some DNA from its telomeres (ends of the chromosomes)

– Implies that clones are born with “old” DNA

• Recent studies have indicated that this may not be the case– Clones had loner

telomeres than original

Transferring genes

• A gene transferred to bacteria is transformed– eg. human insulin grown in bacterial colony

• A gene transferred to another species is transfected– eg. Spider gene in goat allows silk to be harvested

from goat’s milk• Gene therapy involves the replacement of a

faulty allele with a working one

Stem Cells

• The source of the stem cell will determine how far-reaching its adaptive abilities are.

Harvesting Stem Cells

• Pluripotent stem cells are taken from the inner cell mass of a blastocyst.

• Stem cells can be used to replace damaged or diseased cells in almost any part of the body

Therapeutic (non-reproductive) cloning

• Embryos can also be cloned from the healthy cells of a diseased patient to create stem cells of the appropriate blood and tissue type.

Ethical Issues

• Extraction of stem cells destroy what may have been a perfectly healthy embryo.

• Current legislation states that stem cells may only be taken from embryos deemed to be “in excess” during IVF procedures.

• Embryos cannot be created simply for the purpose of harvesting stem cells

Overcoming Infertility

• Infertility problems are usually 50% female, 30-40% male and 10-20% incompatibility.

• Solutions:

1. Donor Sperm– Legally the child belongs to the mother and her

husband at the time of birth

Overcoming Infertility2. IVF (In-vitro fertilisation)– Treats• Low sperm count• Poor swimmers• Damaged fallopian tubes• Hostile mucous• Problems associated with implantation of egg in to

uterine wall

In-vitro fertilisationa) Egg incubated

with sperm in culture fluid

b) Protective band of cells removed from around fertilized egg

c) Embryo returned to mother’s uterus at either the 2 or 4 cell stage

Overcoming Infertility

3. IVF with donor egg4. Surrogacy– Implant IVF fertilised egg in to the womb of another

female

5. GIFT (gamete intrafallopian transfer)– Sperm and eggs unable to meet can be collected and

placed together in the fallopian tube

6. Intracytoplasmic sperm injection– Sperm unable to naturally penetrate egg are injected

In Conclusion

• IVF ethical issues:– What happens to frozen egg, sperm or embryos

after the death of one parent?– On request of the family, can sperm / eggs be

collected from someone after an untimely death?

• Chapter review questions:– Ch. 16: 3-5,7,8,11