qualitative genetics

Question 1

qualitative traits

Answer 1

discrete
typically strong genetic component
controlled by single gene - monogenic
eg - coat colour

Question 2

quantitative

Answer 2

counted or measured
influenced by non-genetic components
controlled by many genes - polygenic
eg = litter size, milk production, disease resistance

Question 3

basic types of gene action

Answer 3

• additive gene action = co-dominant
  phenotype = genotype
  alleles have equal dominance
• non additive gene action
  phenotype does not equal genotype
  alleles either dominant or recessive

Question 4

Mendel’s Laws

Answer 4

law of dominance - some alleles dominant/some recessive
law of segregation - pass on one allele to offspring
law of independent assortment - genes of different traits inherited independently of each

Question 5

non - additive gene action - incomplete (partial) dominance

Answer 5

heterozygous phenotype closer to homozygous dominant phenotype
eg = double muscling

Question 6

linkage

Answer 6

if alleles exist randomly to each other in a population = linkage equilibrium
if alleles do not exist randomly to each other in a population = linkage disequilibrium

Question 7

haplotypes

Answer 7

stretch of DNA (eg several genes) that are inherited together
get shorter over generations

Question 8

other types of gene action

Answer 8

• sex-linked = gene on sex chromosome (opposite = autosomal)
• sex-limited = autosomal gene but phenotype only present in one sex eg milk production
• sex-influenced = phenotype more common in one sex
• genomic imprinting = phenotype depends on the sex of the parent that contributes gene

Question 9

sex-linked genes

Answer 9

usually X-linked - more genes on x chromosome than y
females xx = sex-linked traits similar to autosomal
males xy = single x-traits can affect phenotype even if recessive allele - no paired allele can override

Question 10

x-inactivation

Answer 10

females do not need twice as many x products as males
one copy of the x chromosome becomes inactive in each cell early in embryo development = x-inactivation
the specific x chromosome turned off in each cell is random

Question 11

epistasis

Answer 11

allele at one locus masks or enhances the effect of an allele at another locus - there is an interaction between alleles at different loci

Question 12

pleiotropy

Answer 12

allele at a single locus affects multiple characteristics
one gene = more than one phenotype

Question 13

incomplete penetrance

Answer 13

only a proportion of animals with genotype display phenotype

Question 14

variable expressivity

Answer 14

different degrees of the same phenotype

Question 15

mitochondrial genes

Answer 15

mitochondrial DNA only passed from the mother - affected males cannot pass on condition.