Ch 5-7: Experimental Standardization, Nutrition, Genetic Standardization

Question 1

Sources of between- and within-experiment variation

Answer 1

• the animal itself (age, body weight, number of litter mates…)
• differences in genotype
• fluctuations in (micro)biological, physical, chemical, and social environmental factors
• genotype + primary milieu = phenotype
• phenotype + secondary milieu (pre-experiment conditions) = dramatype
• dramatype + tertiary milieu (experimental procedures) = variation in final outcome

Question 2

Types of diets for lab animals:

Answer 2

• natural-ingredient diets: oats, corn, soya bean, etc.
• chemically defined diets: individual amino acids and specific sugars; expensive,
• purified diets: natural ingedients + pure chemicals and ingredients of varying degrees of refinement; inexpensive, stable;

Question 3

Rat changes in energy requirements under various physiological conditions (daily intake of metabolizable energy in MJ):

Answer 3

• maintenance: 0.45 x body weight^0.75
• growth: 1.20 x body weight^0.75
• pregnancy: 0.6 x body weight^0.75
• lactation: 1.3 x body weight^0.75

Question 4

Coefficient of inbreeding:

Answer 4

• F - the fraction of the original heterozygous genes that have become fixed in a homozygous state during the breeding process.
• delta F (increase in F per generation) depends on the degree of consanguinity of the ancestors

Question 5

A strain can be defined as inbred after…

Answer 5

• 20 gen of either brother-sister mating or mating between offspring & the youngest parent
• at that point F will be 98.4%, meaning that 98.4% of the originally heterozygous loci have become fixed in a homozygous state

Question 6

Negative phenotypical characteristics of inbreeding:

Answer 6

• decreased vigour

- negative effects on growth, survival, fertility

Question 7

The Tryon-effect

Answer 7

• F1 hybrids (resulting from a cross between two different inbred strains) show less uniform responses than those of individuals from the parental strains for certain tasks, which may be due to the improved ability of F1 hybrids to adapt
  (generally, however, they show more uniform responses when morphological/physiological responses are being measured, and less uniform responses for behavioral measures)

Question 8

What is a co-isogenic strain?

Answer 8

• a strain that differs form the established inbred strain by only one differentiating gene (as a result of a mutation).
• very useful for comparisons between two isogenic strains that only differ at the locus of interest
• nomenclature: full strain & substrain designation followed by hyphen and mutant gene symbol (e.g. BALB/cRij-nunu)

Question 9

What is a congenic strain?

Answer 9

• a strain with a genetic trait which has been introduced by repeated backcrossing

Question 10

What is a consomic strain?

Answer 10

(a chromosome substitution strain)

- a whole chromosome is exchanged in an inbred strain by a homologous chromosome of another inbred strain

Question 11

What is a recombinant inbred strain?

Answer 11

• produced by brother sister mating from F2 generation of a cross between two unrelated inbred strains
  (recombinant congenic strains are the same, however those are produced by backcrossing from the second or third generation of two unrelated strains followed by b x s mating)

Question 12

Reasons for using mice instead of other species two create transgenic animals

Answer 12

• many genetically uniform strains available
• a lot of knowledge about genetics, reproduction, in vitro fertilization, embryo manipulation, and transplantation
• good breeder
• lines of ES cells (most frequently used for targeted mutagenesis) are only available for the mouse

Question 13

Describe transgenesis:

Answer 13

• most commonly: adding DNA to the genome by microinjecting DNA-constructs into fertilized oocytes (zygotes)
• one or more copies of the injected DNA will integrate at random sites of the genome, usually as head to tail concatemers
• DNA construct needs to contain promoter sequence, coding sequence, and 3’ translated region of the gene including transcription stop signals
• promoter can be universal, tissue-specific, strong or weak

Question 14

How can multi-copy transgenes be transferred into single-copy transgenes?

Answer 14

• by adding loxP sites to the DNA constructs and crossing the mice carrying multiple copies with mice which are transgenic for Cre recombinase. The enzyme recognises loxP sites and deletes or inverts intermediate DNA sequences

Question 15

What is a mosaic?

Answer 15

• an animal in which a transgene is expressed in only a part of the body’s cells
• they arise when a transgene has integrated into the genome after the first cell division

Question 16

Targeted gene transfer (targeted mutation)

Answer 16

• technique for generating knockout mice
• changed DNA seq is integrated by homologous recombination in ES cells
• transfected ES cells are injected into normal blastocyst
• if ES donors have different fur color than blastocyst donors, the appearance of chimeric animals will signify contribution from the ES cells