8 - Genetic Complexity and Breeding

Question 1

What are some reasons that there might be a variation in chromosome #?

Answer 1

because of number of sets of chr - polyploidy in mammals is lethal
# of individual chr’s in a set

Question 2

What is aneuploidy

Answer 2

Total # of chr is not an exact multiple of a set
Monosome - 1 chr is missing (2n-1)
Trisomy - 1 extra chr (2n+1)
Can be an autosome or sex chr

Question 3

How might aneuploidy occur?

Answer 3

Usually results bc of non-disjunction during meiosis
A pair of chr fail to separate during anaphase I
A pair of chromatids do not separate during anaphase II

Question 4

What happens with monosomy?

Answer 4

Phenotypic changes due to monosomy depend on chr involved
lacking a sex chr is not lethel (turner syndrome (XO)
Missing autosomes is usually lethal
metabolic imbalance - only one unit of expression for one chr

Question 5

What happens with trisomy?

Answer 5

phenotypic outcome is generally not as severe as monosomy
visibility of trisomic animals vary - related to size of chr, larger sizes usually lethal, extra sex chr is not lethal
metabolic imbalances - three units of expression for one chr

Question 6

What are some examples of trisomy?

Answer 6

autosomal trisomy - canine trisomy 13 can cause malignant lymphoma, Trisomy 18 in cattle causes extreme brachygnathia and calves die shortly after birth
Sex chromosome trisomy - XXY or Klinefelter syndrome in cats

Question 7

What is pleiotropy?

Answer 7

A mutation in a single gene can have multiple effects on an individual’s phenotype

Question 8

How does pleiotropy occur?

Answer 8

expression of a gene can affect cell function in more than one way
gene can be expressed in a diff cell types
gene can be expressed at diff stages of development

Question 9

Give an example of pleiotropy about chickens

Answer 9

chickens that have the frizzle gene have feathers that curl outward rather than lying flat
but have trouble regulating body temp, have higher metabolic and blood flow rates, greater digestive capacity and lay fewer eggs

Question 10

Give a pleotropy example about cats

Answer 10

Approve 40% of white cats with blue eyes are deaf (white cats w/ one blue and one yellow eye often deaf on blue side)
White coat color is prod by an autosomal dominant allele (gene also affects iris color and deafness so the gene is called pleiotropic)
mechanism by which the gene affects hearing is being researched - may be related to a lack of ear canal fluod

Question 11

What are quantititative traits?

Answer 11

quantitative traits AKA complex, continuous, polygenic or multifactorial traits
Show continuous variation over a range of phenotypes, several genes contribute to the outcome of a trait, enviro has major impact and majority of traits in animals are quantitative traits

Question 12

What are some examples of quantitative traits?

Answer 12

milk prod, fleece weight, body weight, egg prod, speed, behaviour traits

Question 13

What is inbreeding? Give some examples of first and 2nd degree relatives

Answer 13

Breeding btw related individual
EX. 1st degree relatives (mother-son, daughter-fathers, sibs)
2nd degree (half-sibs, grandparents-grandkits, uncles/aunts to niece/nephews)

Question 14

What is line breeding?

Answer 14

sim to inbreeding but more distant relations (so not first or 2nd degree relatives)

Question 15

What is the result of inbreeding and line breeding?

Answer 15

reduction in heterozygosity and increase in homozygosity
increase in hmozy reveals recessive genes
increase in homo fixes genes so animals more likely to breed true

Question 16

Why might we inbreed?

Answer 16

to fix desirable characteristic
to determine whether an individual is carrier of a recessive allele
lab animals are inbred so lines are genetically identical

Question 17

What is inbreeding depression?

Answer 17

a genetic reduction in vitality and viability of inbred animals

Question 18

why might inbreeding depression occur?

Answer 18

bc of increased homozy and expression of deleterious rec genes
affects fertility and progeny survival

Question 19

What is line crossing/out crossing

Answer 19

mating individuals of the same breed bu diff pedigrees
best method of mating to preserve a breed

Question 20

What is crossbreeding?

Answer 20

mating from diff breeds to provide best genetic diversity
effects include increased heterozy, masking of rec genes, reduce likelihood of breeding true

Question 21

What is hybrid vigour (heterosis)

Answer 21

arises bc of masking of rec genes that depress the viability when homozy
hybrids often have superior performance compared to their parents (seen especially when two inbred lines of animals are mated)

Question 22

What is slective breeding?

Answer 22

refers to programs and procedures designed to modify traits in domesticated species (human driven, breeder chooses parents that possess traits desirable to humans)
selective breeding can dramatically modify traits
ex. dog breeds - all descended from wild wolf-like ancestor

Question 23

Why might we analyze pedigrees?

Answer 23

a method of selecting for eliminated dz-causing allels
can avoid breeding from a line that has shown dz trait in their pedigree
not all animals whose ancestors were affected will inherit the mutated gene, so may miss out on some beneficial traits as well

Question 24

Why might we perform molecular genetic screening?

Answer 24

as a method of selection for eliminated dz-causing alleles
AKA DNA testing
detecting a particular gene in a sample of DNA
can detect carriers and homozy individuals, useful for rec traits
Must know DNA sequence for the dz-causing gene or must ID DNA markers linked to the dz-causing locus
test for one breed may not be applicable to another
new mutations may occur