Conservation Genetics

Question 1

Problems in conservation
genetics 1. Survival of small populations

Answer 1

E.g. Javan black rhinoceros (Rhinoceros sondaicus)
* 40-60 individuals of subspecies in Java
* Another population of <8 in Cat Loc reserve, Vietnam
* No individuals in captivity
* Brink of extinction

GENETIC INSTABILITY
* Not just animals
* Remote tribes of humans “uncontacted tribes”
* Often small populations, inbreeding can be a problem

Question 2

2. Survival of managed populations

Answer 2

E.g. Zoos
* Typically contain very small numbers of individuals of the
same species, subject to inbreeding
* Siberian tigers: ~300 left in the wild in Russia and China,
~200 in Zoos
* The issue is many of the “Zoo’s 200” have come from a
small number of individual founders

Question 3

3. Conservation of breeds

Answer 3

E.g. Domestic animals – dogs, cats, horses, cattle etc.
* Highly inbred
* Bred for particular traits e.g. high milk yield in dairy cows,
desirable characteristics in pet dogs
* Because of this inbreeding, they behave like small
populations and are subjected to inbreeding depression
Reduction in reproductive fitness
Reduction in survivability

Question 4

Inbreeding Depression
What happens in the next generation?

Answer 4

Reduced heterozygosity and reduced hybrid vigour

Question 5

Siberian Tigers
Inbreeding vs. Hybrid Vigour

Answer 5

• Siberian tigers: the Hengadoahezi tiger breeding centre
  (China) they bred >200 tigers in captivity since the 1980s
• They are derived from just eight founding individuals
• The observed inbreeding led to physical deformities in
  the offspring e.g. blurred striped pattern, general genetic
  degradation

Question 6

inbreeding vs. Hybrid Vigour in HUMANS

Answer 6

Founder effects example: Retinitis pigmentosa on
Tristan de Cuhna (night blindness)
* Island was first colonised in 1810 by 15 people
– Just one person had night blindness
– Current population today has a high frequency of the condition

Question 7

Inbreeding does two things:

Answer 7

1. Reduces the number of heterozygotes in the population
   (and therefore reduces hybrid vigour)
2. It encourages the accumulation of individuals with the
   double-recessive phenotype
   – If this phenotype is for a harmful trait, it increases the probability
   the harmful trait spreads through the population

Question 8

Measuring inbreeding

Answer 8

• Inbreeding coefficient (F) = probability of two alleles of a
  gene being identical, because they descended from the
  same copy of the alleles in an ancestor
• Between 0 to 1 (or 0-100%)
  F is the degree to which two alleles are more likely to be
  homozygous (AA/aa) than heterozygous (Aa) in an
  individual, because their parents are related

Question 9

1. Population size

Answer 9

• Effective population size Ne
• The key measure of population size is the number of
  individuals that are able to breed Ne
• If all the rhino’s were male, there would be no potential
  for breeding
• If all the rhino’s were too young/old to mate, there would
  be no breeding
• Ne accounts for sex ratio and population age structure

Question 10

2. Inbreeding

Answer 10

– Inbreeding coefficient F
Measuring inbreeding

Question 11

Conservation of populations
3 Situations

Answer 11

1. Unmanaged population – random breeding
2. Managed population – zoos, wildlife parks etc.
3. Wild animals – mate choice
   * E.g. Sorraia, a horse breed native to Portugal
   – During 1900s the breed was approaching extinction
   – In 1937 it was conserved: only 5 males, 7 females left
   – Horses were allowed to randomly interbreed
   – By 2001, 160 animals living derived from 7 females

Question 12

Ex situ conservation

Answer 12

– When you look at the family pedigrees, you see that
only families derived from two particular females had
survived to the current generation
– The remaining five died out, so the remaining
population is highly inbred
– Genetic bottleneck

Question 13

2. Managed population – zoos, wildlife parks etc.

Answer 13

• Pedigree
• Choose mates that maximise outbreeding
• Studbook (or electronic equivalent)

Question 14

3. Wild animals

Answer 14

Mate Choice

Question 15

How to measure genetic variation in populations?

Answer 15

1. Pedigree – not always available or known, more useful for
   captive populations
2. Genetic testing – techniques similar to DNA fingerprinting
   in humans using microsatellites or minisatellites
   Measuring genetic variation
   * Microsatellite DNA – repeat unit length of 1-7 bases
   – 5-100 repeats at each microsatellites
   – 1000s of different microsatellites, randomly scattered throughout
   genome
   Measuring genetic variation
   * Microsatellite DNA – repeat unit length of 1-7 bases
   – 5-100 repeats at each microsatellites
   – 1000s of different microsatellites, randomly scattered throughout
   genome
   * Minisatellite DNA – repeat unit length of 6-100 bases
   – 2-1000s repeats at each minisatellite
   – 1000s of different minisatellites, scattered throughout genome,
   but often clustered near the ends of chromosomes (telomeres)
   Measuring genetic variation
   * Microsatellite DNA – repeat unit length of 1-7 bases
   – 5-100 repeats at each microsatellites
   – 1000s of different microsatellites, randomly scattered throughout
   genome
   * Minisatellite DNA – repeat unit length of 6-100 bases
   – 2-1000s repeats at each minisatellite
   – 1000s of different minisatellites, scattered throughout genome,
   but often clustered near the ends of chromosomes (telomeres)