실험동물학

• Reasons why we often use mice in the lab:

  1. They're mammals and may replicate human biological system
  2. Easy to breed, feed, and house
  3. Can acclimatize to human touch
  4. Mice are genetically close to humans
• Taxonomy:

  1. Order
  2. Sub-Order
  3. Family
  4. Sub-Family
  5. Genus
  6. Species
• The majority of laboratory mice today have a genetic background that is a mix of European fancy mice and East Asian fancy mice. Genetic analyses have indicated that the maternal origin of most common laboratory mouse strains was the European Mus musculus domesticus subspecies group.
• Mouse and Human Genome Comparison:

  1. Both genomes are 2.5 to 3 billion bp long
  2. 99% of genes have homologs
  3. 95% of their genome is syntenic - occurs on the same chromosome.
• "Classical inbred strains":

  1. Have been inbred for at least 60 generations through brother-sister mating, making them highly homozygous and genetically indistinguishable from their siblings.
  2. Have become the standard strains used in most areas of mouse biology research. E.g., C5JBL/6J
  3. They all carry identical mitochondrial DNA from domesticus.
  4. Most are a mosaic of domesticus, musculus and castaneus - the most prominent being domesticus.
• Mouse and Rat:

  1. Both reach sexual maturity around week 6 to 8.
  2. Their estrus cycle lasts around 4 to 5 days.
  3. Mouse gestation (pregnancy) lasts around 19 to 21 days while rat lasts around 19 to 23 days.
  4. Both nurse their young for around 3 weeks.
• Life span of a mouse/rat is around 2 to 3 years.
• • Rats and mice are nocturnal animals
  • They mainly sleep during the daytime
  • Their hormones fluctuate considerably according to the time
• Ways rats and mice thermoregulate:

  1. They have no sweat glands, which means heat can't be dissipated by sweating or panting.
  2. In extreme situations, they would moisten their fur with saliva to cool down but this can lead to dehydration
  3. Amount of circulation is usually increased in hairless areas like tail and ears while areas with fur decrease their circulation.
• • Rats and mice eat their own feces in order to absorb undigested nutrients.
  • If coprophagy is decreased, their growth would be retarded by 10 to 20%
• • Pheromones are present in male mice's urine
• • Pheromones are present in male mice's urine
  • Lee-Boot Effect: Estrous cycles of female rodents are suppressed or prolonged when they are housed in groups and isolated from males.
  • Whitten Effect: Estrous cycles of female mice are synchronized when they are exposed to pheromones from male mouse urine.
  • Bruce Effect: Female mice terminate their pregnancy or fail to implant when they are exposed to the scent or presence of an unfamiliar male shortly after mating.
• Bruce Effect stops the female from wasting energy on babies that might get hurt by the new male, helping her have successful babies. Different animals might have slightly different reasons for it, but the main idea is the same: not having babies with a new male around.
• Ways to detect estrus in female albino mice:

  1. swollen vaginal tissue
  2. gaping vaginal opening
  3. moist tissues
  4. bright pink/purple mucous membrane

  
• Non-estrus in female albino mice:

  1. No swelling of the vaginal tissue
  2. Closed vaginal opening
  3. Dry vaginal tissues
  4. Pale mucous membranes

  
• The estrous cycle causes hormonal and physical changes in the female reproductive organs and these changes usually occur in a cyclical pattern, with the cycle typically lasting 4-5 days in mice and rats. In those 4-5 days, pregnancy is only viable for just a day.
• The presence of a copulatory plug is an indication of successful mating in mice. It is also most often referred to as the vaginal plug. It is made of several different components such as sperm, ejaculation fluid, and mucus. However, it does not guarantee that conception has occured.
• Rodent pup sexing:

  1. Males have twice the anogenital distance that females have.
  2. The nipple line on females is identifiable as early as day 8 or 9.
  3. Once hair is present on Day 9, the area between the testicles and anus is completely covered with hair; in females, the area is defined as a hairless line between the vaginal opening and anus.

  
• The Three Laws of Heredity:

  1. Law of Dominance
  2. Law of Segregation
  3. Law of Independent Assortment
• Forward genetics (phenotype -> genotype):

  1. Starts with an observed phenotype and aims to identify the genes that is influencing the phenotype.

  Reverse genetics (genotype -> phenotype):

  1. Starts with a known gene or genetic sequence and aims to determine its function by analyzing the resulting phenotype.
• • homozygote = having two identical alleles of a particular gene, e.g. AA
  • heterozygote = having different alleles of a particular gene, e.g. Bb
  • hemizygous =  the condition of having only a single allele of a gene or chromosome (isn't the same as haploinsufficiency)

  
• Loss of functional alleles come in three types:

  1. null (amorph) = complete loss of function, produces no gene product
  2. hypomorph = partial loss of function, some gene product or activity is present but less than wild-type
  3. Antimorph (dominant-negative) = troublemaking mutation that's strong enough to mess things up even when there's a normal version of the gene around.
• Gain of functional alleles comes in two types:

  1. Hypermorph = increase in function, produces higher levels of gene product or gene product with increased activity or unregulated activity. Usually dominant.
  2. Neomorph = gaining of a new function, produces gene product with a new activity. Cab be dominant or recessive
• What is polymorphism in biology?


  Polymorphism in biology refers to the presence of different versions or looks within one group of animals or plants.
• How does polymorphism differ from mutation?

  Mutation refers to a change in a single individual, while polymorphism is about the whole group having different options.
• What are the sources of polymorphism?

  The differences can come from genes (like inherited traits) or from the environment (like diet or climate).
• Penetrance is about how likely it is for a gene to show its effect, and it can vary from everyone showing it to only some people showing it.
• What is complete penetrance?

  Complete penetrance occurs when everyone who has a specific gene shows the associated trait or disease.
• Can you give an example of reduced penetrance?

  Sure, the BRCA1 mutation increases the risk of breast cancer, but not everyone with the mutation will develop the disease, showing reduced penetrance.
• What does non-penetrance mean?

  Non-penetrance happens when some people with a certain gene don't show the associated trait or disease at all.
• Haploinsufficiency describes a situation where having only one functional copy of a gene is not enough to maintain normal function.
• What is co-dominance in genetics?

  Co-dominance in genetics is when neither allele is dominant over the other, so both alleles have equal influence on the trait's appearance.
• An example of co-dominance?

  The ABO blood groups in humans are a classic example of co-dominance. If someone has both A and B alleles, their blood type is AB, and they have both A and B antigens.
• How does co-dominance differ from incomplete dominance?

  In co-dominance, both alleles are equally strong, so you see both traits distinctly. In incomplete dominance, the traits blend together, creating an intermediate trait.
• Why is co-dominance considered non-Mendelian?

  Co-dominance doesn't follow the simple dominant-recessive patterns described by Gregor Mendel because both alleles are expressed fully, rather than one being dominant over the other.
• What is epistasis in genetics?

  Epistasis in genetics is when one gene's actions depend on whether another gene is present or not, like one gene masking or altering the effects of another.
• How does epistasis differ from Mendel's genetic rules?

  Epistasis doesn't follow Mendel's simple dominant-recessive patterns. Instead, it's about one gene overriding or hiding the effects of another.
• How would you explain epistasis in simpler terms?

  Epistasis is like one gene saying, "Hey, I'm in charge here!" and masking the effects of another gene, affecting how traits show up in living things.
• • A phenocopy is an environmentally-induced phenotype that is identical or similar to a genetically-determined phenotype but without the underlying genetic change.
  • They're not passed down to kids because they're not from genes.
  • Examples include rabbits whose fur changes color because of temperature and flies that turn yellow because of chemicals.
• What is gene dosage and X-chromosome inactivation?

  Gene dosage and X-chromosome inactivation are processes that ensure both males and females have similar amounts of certain genes, despite having different sex chromosomes.