Genetics of Quantitative Characters Flashcards
What were the discoveries of Galton regarding human height?
- Compared heights of parents to their children
- Found tall parents had tall children vice versa
- Found regression toward the mean
What is meant by a Regression toward the Mean?
In the case of Galton and human height, the children will tend to be closer to the average height of the population than an intermediate between their parents height.
What is meant by a Normal Distribution?
The characteristic bell shape curve, that is a statistical distribution . Shows the deviation of individuals from the mean is symmetrical.
Give an example of a trait showing the Normal Distribution
Frequency of Cerebrovascular Incident (stroke) and blood pressure. BP is normally distributed, those over a certain threshold are likely to suffer.
What is the formula for variance?
∑(x-¯x)^2/n
Define Heritability
The proportion of the total variation in a population that’s due to genetic variation.
What is the formula for Broad sense Heritability?
H^2 = Vg/ Vg + Ve + Vge
What is the formula for Phenotypic Variance?
Vp = Vg + Ve + Vge
What is the term Vge?
Vge takes into account the norms of reaction
Give an example of Gene and Environment interaction.
Achillea- a yarrow plant different lines will grow preferentially at different heights above sea level. Very different response of genotype to height.- different norms of reaction
Give another example of Gene and Environment Interaction.
Maize- modern varieties grow much better than old ones with fertiliser but much worse in the absence of fertiliser.
Define the term Norms of Reaction.
Describes the pattern of phenotypic expression of one genotype across a range of environments.
Define Narrow Sense Heritability.
Narrow Sense describes the proportion of phenotypic variance that is due to Additive Variance.
Define Additive Variance.
The genetic component of variance responsible for parent-offspring resemblance.
Define Dominance Variance
The presence of a dominant allele causes an added variation- DD and Dd have the same phenotype.
Define Interaction Variance
The variance caused by the interaction of one gene with another (effects are altered)
What is the Formula for Narrow Sense Heritability?
H^2 = Va / Vg + Ve + Vge
Why would a high additive variance be useful in agriculture?
High Va suggests a rapid response to selection- high resemblance of parents to offspring
What is Pellagra an an example of?
An eg. of how a condition can be familial but NOT heritable- no genetic component. Caused by a deficiency in Vitamin B3 (niacin)
Define Covariance
A measure of how much two variables change together.
What is the formula for Covariance?
∑ (x-xM)(y-yM)
xM and yM are the means of the two variables
What is the formula for Correlation Coefficient?
Covariance/ (SD of x)(SD of y)
SD = standard deviation
Name three ways in which Heritability can be measured.
Correlation of Relatives, Selection Experiments, Twin Studies
Outline how Correlation of Relatives can be used to measure Heritability .
Closely relatives used i.e. parents, offspring siblings- genetic component is greater so variation in phenotype cane be compared.
Outline how Selection Experiments can be used to measure Heritibalility
Mice- inbred for many generations to produce distinct lines. It was found that these lines have varying willingness to drink from alcohol-supplemented water- bug genetic component in heritability of this trait
Outline how Selection experiments can be used to measure Heritability
The Domestication of the SIlver Fox by Belyaev. 15 generations of inbreeding docile individuals- reduced pigment (melanin) and floppy ears = docile foxes.
Outline how Twin Studies can be used to measure Heritability.
The Concordance method- “How similar to each other for a particular characteristic are MZs compared to DZs? any addition similarity (concordance) is genetic
What is the major effect of Obesity and what are the symptoms?
Diabetes Mellitus- glucose intolerance, affects 5-10% of westerners, glucose in urine, fatigue, thirst and frequent urination
How has the environment played a part in the increase in diabetes?
- drop in the price of food
- increase in the production of processed food
- increase in the availability of transport
What genes are involved in Obesity onset?
The Leptin gene and FTO gene
What has the obese mouse model shown about the role of leptin?
Obese mice are leptin deficient. Leptin is expressed by adipose and received in HT- deficiency means inability to detect fullness (Jackson 1950)
What effect does the FTO gene have on weight gain?
Switched on in HT. Those with AA genotype have SNPs on FTO and are 2.5 kg heavier than TT people (Dina et.al. 2007)
How does the Siamese Cat show gene-environment interaction?
- have a mutation in tyrosinase required for melanin production
- mutated enzyme will only work in cooler regions (extremities) so melanin only made here.
How does the Arctic Hare show gene-environment interaction?
When light intensity is high, melanopsin transcription is increased, HT and SCN receives stimulation and melanin production occurs, opposite occurs when light intensity is low.
How do Humans show gene-environment interaction?
Seasonal Affective Disorder (SAD) light intensity regulated depression. Possibly due to decreased serotonin transcription.
How does the disease Phenylketonuria show Gene-Environment interaction?
PKU = inborn error in ability to metabolise Phenylalanine due to absence of PAH. Effects are completely absent if Pha free diet is applied.
How can Age interact with genes?
Huntington’s- disease only appears in 50+
Give an example of incomplete penetrance.
White and black cats- all have same genotype but varying levels of black and white spots.
