Genetics of Quantitative Characters

Question 1

What were the discoveries of Galton regarding human height?

Answer 1

• Compared heights of parents to their children
• Found tall parents had tall children vice versa
• Found regression toward the mean

Question 2

What is meant by a Regression toward the Mean?

Answer 2

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.

Question 3

What is meant by a Normal Distribution?

Answer 3

The characteristic bell shape curve, that is a statistical distribution . Shows the deviation of individuals from the mean is symmetrical.

Question 4

Give an example of a trait showing the Normal Distribution

Answer 4

Frequency of Cerebrovascular Incident (stroke) and blood pressure. BP is normally distributed, those over a certain threshold are likely to suffer.

Question 5

What is the formula for variance?

Answer 5

∑(x-¯x)^2/n

Question 6

Define Heritability

Answer 6

The proportion of the total variation in a population that’s due to genetic variation.

Question 7

What is the formula for Broad sense Heritability?

Answer 7

H^2 = Vg/ Vg + Ve + Vge

Question 8

What is the formula for Phenotypic Variance?

Answer 8

Vp = Vg + Ve + Vge

Question 9

What is the term Vge?

Answer 9

Vge takes into account the norms of reaction

Question 10

Give an example of Gene and Environment interaction.

Answer 10

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

Question 11

Give another example of Gene and Environment Interaction.

Answer 11

Maize- modern varieties grow much better than old ones with fertiliser but much worse in the absence of fertiliser.

Question 12

Define the term Norms of Reaction.

Answer 12

Describes the pattern of phenotypic expression of one genotype across a range of environments.

Question 13

Define Narrow Sense Heritability.

Answer 13

Narrow Sense describes the proportion of phenotypic variance that is due to Additive Variance.

Question 14

Define Additive Variance.

Answer 14

The genetic component of variance responsible for parent-offspring resemblance.

Question 15

Define Dominance Variance

Answer 15

The presence of a dominant allele causes an added variation- DD and Dd have the same phenotype.

Question 16

Define Interaction Variance

Answer 16

The variance caused by the interaction of one gene with another (effects are altered)

Question 17

What is the Formula for Narrow Sense Heritability?

Answer 17

H^2 = Va / Vg + Ve + Vge

Question 18

Why would a high additive variance be useful in agriculture?

Answer 18

High Va suggests a rapid response to selection- high resemblance of parents to offspring

Question 19

What is Pellagra an an example of?

Answer 19

An eg. of how a condition can be familial but NOT heritable- no genetic component. Caused by a deficiency in Vitamin B3 (niacin)

Question 20

Define Covariance

Answer 20

A measure of how much two variables change together.

Question 21

What is the formula for Covariance?

Answer 21

∑ (x-xM)(y-yM)

xM and yM are the means of the two variables

Question 22

What is the formula for Correlation Coefficient?

Answer 22

Covariance/ (SD of x)(SD of y)

SD = standard deviation

Question 23

Name three ways in which Heritability can be measured.

Answer 23

Correlation of Relatives, Selection Experiments, Twin Studies

Question 24

Outline how Correlation of Relatives can be used to measure Heritability .

Answer 24

Closely relatives used i.e. parents, offspring siblings- genetic component is greater so variation in phenotype cane be compared.

Question 25

Outline how Selection Experiments can be used to measure Heritibalility

Answer 25

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

Question 26

Outline how Selection experiments can be used to measure Heritability

Answer 26

The Domestication of the SIlver Fox by Belyaev. 15 generations of inbreeding docile individuals- reduced pigment (melanin) and floppy ears = docile foxes.

Question 27

Outline how Twin Studies can be used to measure Heritability.

Answer 27

The Concordance method- "How similar to each other for a particular characteristic are MZs compared to DZs? any addition similarity (concordance) is genetic

Question 28

What is the major effect of Obesity and what are the symptoms?

Answer 28

Diabetes Mellitus- glucose intolerance, affects 5-10% of westerners, glucose in urine, fatigue, thirst and frequent urination

Question 29

How has the environment played a part in the increase in diabetes?

Answer 29

- drop in the price of food - increase in the production of processed food - increase in the availability of transport

Question 30

What genes are involved in Obesity onset?

Answer 30

The Leptin gene and FTO gene

Question 31

What has the obese mouse model shown about the role of leptin?

Answer 31

Obese mice are leptin deficient. Leptin is expressed by adipose and received in HT- deficiency means inability to detect fullness (Jackson 1950)

Question 32

What effect does the FTO gene have on weight gain?

Answer 32

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)

Question 33

How does the Siamese Cat show gene-environment interaction?

Answer 33

- have a mutation in tyrosinase required for melanin production - mutated enzyme will only work in cooler regions (extremities) so melanin only made here.

Question 34

How does the Arctic Hare show gene-environment interaction?

Answer 34

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.

Question 35

How do Humans show gene-environment interaction?

Answer 35

Seasonal Affective Disorder (SAD) light intensity regulated depression. Possibly due to decreased serotonin transcription.

Question 36

How does the disease Phenylketonuria show Gene-Environment interaction?

Answer 36

PKU = inborn error in ability to metabolise Phenylalanine due to absence of PAH. Effects are completely absent if Pha free diet is applied.

Question 37

How can Age interact with genes?

Answer 37

Huntington's- disease only appears in 50+

Question 38

Give an example of incomplete penetrance.

Answer 38

White and black cats- all have same genotype but varying levels of black and white spots.