Polygenic inheritance

Question 1

Define polygenic inheritance?

Answer 1

Inheritance of single train that is controlled by 2 or more genes

Question 2

Define multifactorial disease

Answer 2

Disease that has resulted from interaction of genetic & environmental factors

Question 3

E.g. of characteristics that follow polygenic inheritance?

Answer 3

Height

weight

skin colour

Question 4

If polygenic characteristic was plotted on a graph, what shape would the graph be? Why?

Answer 4

Continuous, normal distribution, bell shaped curve

Phenotype is determined by many genes at different lotion a chromosome- each alley has small additive effect

Leeds to different variations= continuous

Question 5

Define concordance rate

Answer 5

The probability that 2 people w/ shared genes will develop same disease

Used to examine how genetically linked disease is

High concordance rate= trait has strong genetic influence

Low concordance= high environmental influence i.e epigenetic

Question 6

How to interpret concordance rates?

Answer 6

MZ concordance higher than DZ concordance= disorder has genetic component

MZ concordance same or similar to DZ- disorder is environmentally caused

MZ concordance is 100%- disorder is genetically caused

MZ concordance is less than 100%- disorder has environmental component

Question 7

Common multifactorial diseases?

Answer 7

Diabetes- Type 1 &2

Hypertension

Heart disease- caused by coronary heart disease

Stroke

Breast cancer

Question 8

What is the concordance rate for MZ twins & DZ twins for Type 1 diabetes?

Answer 8

MZ= 30-70%- suggests diabetes 1 has significant genetic factor.

DZ= 5-10%

Question 9

Which alleles & genes are linked to causing Type 1 diabetes?

Answer 9

HLA class II alleles- involved in T cell recognition

Insulin gene- tandem repeat polymorphism in this gene affects transcription

Tandem repeat= sequence of.2 or more DNA base pairs that are next to each other

Question 10

What is concordance rate for MZ twins * DZ twins for Type 2 diabetes?

Answer 10

MZ= 35-60%

Mz is higher than DZ

Question 11

Which alleles & genes are linked to causing type 2 diabetes?

Answer 11

TCF7L2 gene- codes for transcription factor involved in secreting insulin

variant of this gene increases risk of type 2 by 50%

Question 12

What environmental factor plays role in Type 2 diabetes ?

Answer 12

Obesity- significant risk factor

influenced by diet & exercise levels

although genes can play role in obesity too

Question 13

What is the heritability estimate for hypertension w/in families? What does value suggest?

Answer 13

Heritability estimates= 30-50%

This is less than 100%= so environmental factors contribute to high blood pressure

Question 14

What environmental factors add to risk of getting hypertension?

Answer 14

Sodium intake

reduce physical activity

obesity

psychosocial stress

Question 15

What genetic factors lead to Increased risk of hypertension?

Answer 15

Blood pressure is regulated by many systems- kidney function, cellular ion transport & heart function- these systems are controlled by genes

more than 20 genes linked to hypertension- many affect reabsorption of water & salt in kidney, affects blood vol & pressur

Question 16

Give general heritability estimate for heart disease

Answer 16

Person w/ positive family history of CAD is X@ likely to suffer w/ CAD compared w/ someone with no history

Question 17

What environmental factors increase risk of heart disease?

Answer 17

Diet- obesity, cholesterol

Smoking

Hypertension

Question 18

What genetic factor adds to risk of getting heart disease?

Answer 18

LDL receptor gene mutations- doubles cholesterol levels in body

Condition called familial hypercholesterolemia

High levels of LDL lead to atheroma- causes blockages in coronary artery

Question 19

What is risk of having strokes if you have positive family history? Concordance rates?

Answer 19

Risk of having a stroke increases by x 2-3 if 1 parent has had a stroke.

Twin studies show concordance rate for MZ was 10% & for DZ twins it was 5%
- Suggests that environmental factors are important too

Question 20

What genetic factors add to risk of stroke?

Answer 20

More than 12 single-gene disorders can cause a stoke
- e.g. Sickle Cell Disease - caused by mutation of HBB gene - causes RBCs to get stuck in blood vessels.
- e.g. Haemophilia- mutation of F8 causes Heamophilia A which causes altered or missing coagulation factor VIII.

Question 21

What environmental factors can increase risk of stroke?

Answer 21

-Diabetes

Hypertension

Obesity

Question 22

What is risk of getting breast cancer is relative has it?

Answer 22

risk doubles

Question 23

What environmental factors influence cancer?

Answer 23

EF can induce mutations

Tobacco accounts for 1/3 of all cancer deaths in HIC

Radiation

chemicals- carcinogens

Question 24

What genetic mutations are linked to breast cancer?

Answer 24

Mutations in BRCA1 & BRCA2 genes- involved in DNA repair