Lecture 19 - Selecting

Question 1

characteristics of outcrossing species

Answer 1

-difficult to inbreed and prone to inbreeding depression
-not typically selfed to produce homozygous lines
-treated as heterozygous/heterogenous populations (or hybrids)

Question 2

inbreeding depression

Answer 2

the reduction in performance associated with an increase in homozygosity (possibly due to unmasking of recessive alleles)

Question 3

effects of inbreeding depression

Answer 3

increased homozygosity, reduced height, seed set, disease resistance, increased lodging

Question 4

what is the main focus when breeding outcrossing crops

Answer 4

population rather than identification of superior individuals

Question 5

what does it mean if something does not breed true

Answer 5

there will be variability within each parent, so offspring will not be the same

Question 6

recurrent selection

Answer 6

cyclical selection scheme that is designed to concentrate desirable alleles by selecting best individuals in a population (mass selection plus intermating)

Question 7

types of recurrent selection

Answer 7

phenotypic and genotypic

Question 8

phenotypic recurrent selection

Answer 8

selection based on visual observation of traits (like mass selection)

Question 9

genotypic recurrent selection

Answer 9

insight into genotype based on potential of plant as a parent (selection based on performance of progeny or molecular markers)

Question 10

2 ways of gaining 2-parent control

Answer 10

-self plant and examine progeny (inbreeding is a concern)
-test cross to a known tester line and find expression of alleles

Question 11

combining ability

Answer 11

a measure of the ability of parental gametes to produce superior progeny

Question 12

general combining ability

Answer 12

the ability of a parental genotype to produce superior progeny in ANY cross

Question 13

specific combining ability

Answer 13

the ability of a parental genotype to produce superior progeny in ONE particular cross

Question 14

how is GCA and SCA measured

Answer 14

test or top cross so that 50% of parentage is well known

Question 15

GCA is a measure of ___________ gene action

Answer 15

additive

Question 16

SCA is a result of _______ gene action

Answer 16

non-additive

Question 17

heterosis

Answer 17

increased vigour and productivity shown by progeny in comparison to parental values

Question 18

2 main theories to explain heterosis

Answer 18

dominance and over-dominance

Question 19

overdominance theory of heterosis

Answer 19

heterosis results from heterozygous condition, suggesting a physiological or gene expression basis associated with heterozygosity

Question 20

dominance theory of heterosis

Answer 20

vigor is due to accumulation of favorable dominant alleles in an individual (dominant alleles at 5 loci>dominant alleles at 3 loci)