18.3.417-18 · Selection, Evolution, Classification and Conservation
Assisted Reproduction — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions
5 min read 10 parts Lesson 34 of 36 Unit quiz
Lesson summary
18.3.4 Assisted Reproduction — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe IVF, embryo transfer and surrogacy and explain their use in conserving endangered mammals.Endangered mammals tend to have small, isolated populations.Small populations are prone to…
- Inbreeding depression
- Artificial insemination
- Cryopreservation
- Whole ecosystems
- Conservation
- Extinction
Part 1 of 8The problem for endangered mammals
Endangered mammals tend to have small, isolated populations.
Inbreeding depression
Small populations are prone to inbreeding and inbreeding depression.
- Inbreeding depression
- reduced fitness of a population due to breeding between close relatives and the resulting increased homozygosity.
Isolation makes it hard for individuals to find suitable mates.
Large mammals were once moved between zoos for breeding.
- Advantagethe health of mother and foetus could be monitored.
- Disadvantageit was highly expensive and unreliable because individuals sometimes refused to mate.
Part 2 of 8In vitro fertilisation (IVF)
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A needle is inserted into the female's ovaries to extract eggs.
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The eggs are kept briefly in culture medium.
3
Male semen is mixed with the eggs so fertilisation occurs.
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Several zygotes form and develop into embryos.
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The embryos are cultured for several days.
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The embryos are transferred into the mother or another female.
Part 3 of 8Advantages of IVF
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It lets humans control and confirm fertilisation, unlike natural mating.
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It is useful when animals will not mate or are far apart.
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Embryos can be frozen for later use.
4
IVF is best known as a human technique for infertility, but is important for conserving non-human species too.
Part 4 of 8Embryo transfer
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An egg from a female of the endangered species is fertilised by sperm from a male of the same species.
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A zygote forms and develops into an embryo.
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After fertilisation the embryo is taken from the female's uterus.
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It is transferred to a surrogate female.
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The embryo develops to full term and the offspring is born.
Part 5 of 8Why embryo transfer is used
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Pregnancy is high risk for females and complications can be fatal.
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Each reproductive female of an endangered species is very valuable because numbers are low.
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Embryo transfer spares the vulnerable female the risks of pregnancy, so she can provide eggs for many offspring.
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The surrogate can be of a non-vulnerable species, e.g. in conserving African antelope species.
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Females may be given FSH to stimulate several follicles (superovulation).
Part 6 of 8Surrogacy
Surrogate
- Surrogate any female that becomes pregnant with another female's embryo and carries it to full term.
Surrogates need hormone treatment first so the uterus is ready for the embryo to embed.
Artificial insemination
The embryo may have been conceived naturally, by artificial insemination or by IVF.
- Artificial insemination
- semen from the male is injected into the uterus of the female.
A surrogate can be the same or a different species.
- A different species must be closely related to ensure compatibility of embryo and uterus.
Part 7 of 8Other techniques and limitations
Cryopreservation
- Cryopreservation gametes and embryos stored in liquid nitrogen at −196 °C in gene banks.
Cloning
- Cloning somatic cell nuclear transfer gives identical animals but no new genetic variation.
Limitations: low success rates, high cost, species-specific techniques and surrogate availability.
They do not address the cause of decline, such as habitat loss.
Captive-raised offspring may lack behaviours needed to survive in the wild.
Part 8 of 8More from the specification
More from the specification
Conservation in national parks and marine parks
- Conservation in national parks and marine parks preserving endangered wildlife species within national parks and marine parks includes storing botanical seeds in seedbanks.
Native species
- A species that naturally lives in an ecosystem.
National park
- Government-protected area with controlled human access.
Marine park
- Protected area of water set up for marine conservation.
Conservation
- Protecting species and habitats.
Extinction
- Loss of every member of a species.
Biodiversity
- The number of different species in an area.
Competition
- Two organisms needing the same limited resource.
Extinct
- No longer existing anywhere.
Invasive species
- A species introduced to a habitat where it spreads and causes damage.
Genetic diversity
- The range of alleles within a population.
Climate change
- Long-term changes in temperature and weather patterns.
Whole ecosystems
- Whole ecosystems conserving them,
- such as rainforests and coral reefs threatened by development, pollution and exploitation, is essential for species survival.
Key terms
| Term | Meaning |
|---|---|
| Inbreeding depression | Reduced fitness from breeding between close relatives and increased homozygosity. |
| IVF | Fertilisation of an egg outside the female body. |
| Embryo transfer | Moving an embryo to the uterus of a surrogate female. |
| Surrogate | Female that carries another female's embryo to full term. |
| Artificial insemination | Injecting semen into the uterus of a female. |
| Cryopreservation | Storing gametes or embryos at very low temperatures. |
Avoid these mistakes
1
Saying IVF happens only in humans — it is also used to conserve endangered species.
2
Saying the surrogate can be any species — it must be closely related.
3
Forgetting hormone treatment of the surrogate — her uterus must be ready for implantation.
4
Saying assisted reproduction solves habitat loss — it only helps numbers and genetic mixing.
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