Assisted Reproduction (Cambridge International A-Level Biology)

Spec point — 18.3.4 · describe methods of assisted reproduction used in the conservation of endangered mammals, limited to IVF, embryo transfer and surrogacy

Assisted reproduction

• Endangered mammals tend to have small and isolated populations

• Small populations are prone to inbreeding and inbreeding depression

  • Inbreeding depression is the reduction in fitness of a population due to breeding between closely related individuals and the resulting increased homozygosity

• When populations are isolated it can also be difficult for individuals to find suitable reproductive mates

• Previously large mammals were transported between zoos in captive breeding programs

  • Advantage: Humans were able to monitor the health of the mother and foetus
  • Disadvantage: It was highly expensive and unreliable as sometimes individuals would refuse to mate

• Science has come up with several solutions for inbreeding and the lack of reproductive mates in endangered mammals

IVF

• In vitro fertilisation involves the fertilisation of an egg outside of the female body

  • For example in a test tube or petri dish

• Method:

  • A needle is inserted into the female’s ovaries and eggs are extracted
  • The eggs are kept in a culture medium for a short amount of time
  • Male semen is mixed with the eggs so fertilisation can occur
  • Several zygotes form and develop into embryos
  • The embryos are placed in a culture for several days
  • The embryos are transferred either into the mother, or another female

• IVF is advantageous over natural mating because it allows humans to control and confirm fertilisation of the embryo

Embryo transfer

• Pregnancies are high risk for females; complications can arise which in some cases prove fatal

• Since the population numbers of an endangered species are already very low each reproductive female is of very high value and importance

• Embryo transfer can be used to avoid the risks of pregnancy for the vulnerable female so that she can provide many eggs for multiple offspring

• Method:

  • An egg belonging to a female of the vulnerable species is fertilised by the sperm belonging to a male of the same species
  • A zygote forms which develops into an embryo
  • After fertilization, the embryo is taken from the uterus of the female and transferred to a surrogate female
  • The embryo develops to full term and the offspring is born

• The surrogate mother can be from another non-vulnerable species

• This technique has been used to try and conserve populations of several different species of African antelope

Surrogacy

• A surrogate is any female that becomes pregnant with the embryo from another female and carries the embryo to full term

• Surrogate mothers require hormone treatment before they receive an embryo

  • The hormones ensure that her uterus is in the right condition for the embryo to embed

• There are multiple ways in which the embryo might have been conceived:

  • Naturally
  • Artificial insemination (semen from the male is injected into the uterus of the female)
  • IVF

• A surrogate female can be the same or different species to the biological mother of the embryo

  • If it is a different species it needs to be closely related to ensure compatibility of the embryo and uterus

Exam Hint IVF is most commonly discussed as a human technique for treating infertility. However, make sure to recognise its importance in conservation of endangered (non-human) species.