Plant Breeding - Guido Flashcards
What are the three phases of crossing genotypes to produce a progeny
- Identify populations / collections of germplasm characterized by genetic variability
- Select individuals with superior phenotypic characteristics
- Develop improved varieties from these individuals
What is a quantitative character
a measurable character, with a continuous distribution of phenotypes (polygenic, multifactorial or complex
characters)
Phenotypes are produced by
the action of many genes and their interaction with the environment
What is QTL - Quantitative Trait Loci
Genomic regions containing genes associated with a quantitative character are known
Can different genotypes have the same phenotype
Yes, Many different genotypes can have the same phenotype
The greater the number of loci involved in
determining a character, the________the
number of possible genotypes
greater
Inheritability is defined as the relationship between
phenotypic variation, due to environmental and genetic causes
Inheritance refers to the process by which genetic information is passed from parents to their offspring
heritability refers to the proportion of the variation in a particular trait within a population that can be attributed to genetic factors. It is a statistical measure that estimates the extent to which differences in a trait among individuals can be attributed to genetic variation
Why cant the influences on the phenotype be broken down into genetic
and environmental components
because the expression of the genotype depends on the environment in which the plant grows
total phenotypic variance equation
VP = VG + VE + VGxE
VP: variance in phenotype
VG: genetic variance
VE: environmental variance
VGxE: genetic variance x environ. variance
phenotype
plant traits, everything you can see, until you can prove it is genetics inherited
another word for genotype propagation
cloning
additive genetic variances (VA)
additive effects that can be added to determine the overall effect on
the phenotype
Genetic variance due to dominance (VD)
genes with a dominant component - the effect of an allele depends on the identity of the other allele for the same locus
Genetic variance due to interaction (VI)
genes that interact with each other having epistatic (completely new) effects - which is not present when the action is limited to single genes
genetic variance equation
VG = VA + VD + VI
VG: variance in genetics
VA: additive genetic variances
VD: genetic variance due to dominance
VI: genetic variance due to interaction
phenotypic variance (VP)
attributed to differences between the population genotypes
environmental variance (VE)
due to non-genetic factors, such as different amounts
of light
The variance due to the genotype - environment interaction (VGE)
occurs when the effect of a gene depends on the specific environment in which it is found
The total phenotypic variance equation
answer: VP = (VA + VD + VI) + VE + VGxE
because:
VP = VG + VE + VGxE
VG = VA + VD + VI
VP: variance in phenotype
VG: genetic variance
VE: environmental variance
VA: additive genetic variances
VD: genetic variance due to dominance
VI: genetic variance due to interaction
Broad sense inheritability (H2 or hb2)
-equation
-definition
-ranges
H2 = VG / VP
-the portion of phenotypic variance determined by total genetic variance
-H2 ranges from 0 to 1
VG: genetic variance
VP: variance in phenotype
Explain the range for broad AND narrow sense inheritability and what it means
0 = differences due solely to environment
1 = differences due solely to genetics
closer to 1 the greater the genetic component
narrow sense heritability (hn2)
-equation
-definition
-ranges
hn2 = VA / VP
-phenotypic variance directly transmitted from parents to offspring
-always less than or equal to broad-sense heritability.
Broad-sense heritability accounts for total genetic variance (additive, dominant/recessive, and interactive), while narrow-sense heritability only accounts for additive genetic variance.
-ranges 0-1 (The closer to 1, the greater the Additive genetic component)
How can you estimate inheritability in a broad sense - through variance decomposition
by eliminating one of the components of the
variance; make VG or VE 0
VG = 0 by cultivating genetically identical individuals (preferred)
VE = 0 by all individuals cultivated in the same environmental
conditions (NOT possible)