Genetic Basis of Disease (Lectures 9 – 11)

Question 1

Difference between sex-linked and autosomal inheritance

Answer 1

Sex-linked inheritance involves genes on the sex chromosomes (typically X). Disorders like red-green color blindness are X-linked and more common in males.
Autosomal inheritance refers to genes on non-sex chromosomes (autosomes). Disorders can be dominant (e.g., Achondroplasia) or recessive (e.g., Phenylketonuria).

Question 2

Meaning of dominance and recessiveness

Answer 2

A dominant allele expresses its trait with just one copy (heterozygous).
A recessive allele must be present in both gene copies (homozygous) to manifest the trait.
Achondroplasia = dominant example, PKU = recessive example.

Question 3

That mitochondria have genes

Answer 3

Mitochondria carry their own DNA, inherited maternally.
Mutations in mitochondrial genes affect energy production and can cause mitochondrial diseases.

Question 4

Difference between simple and complex genetic diseases

Answer 4

Simple (monogenic) diseases result from mutations in a single gene (e.g., CF, SMA).
Complex (polygenic) diseases involve many genes and environmental factors (e.g., obesity, schizophrenia).

Question 5

That cancer is a genetic disease

Answer 5

Cancer is driven by mutations in genes regulating the cell cycle, growth, and apoptosis.
Mutations in oncogenes or tumour suppressor genes disrupt normal control, leading to uncontrolled cell growth.

Question 6

Health and disease as an interaction between genes and environment

Answer 6

Traits like obesity or schizophrenia reflect an interaction: genetic predispositions + lifestyle/environmental influences.
Genetics loads the gun, environment pulls the trigger.

Question 7

Basic properties of the human genome

Answer 7

The human genome has ~20,000 genes across 23 chromosome pairs (22 autosomes + X/Y).
Genetic diversity arises from SNPs, alleles, recombination, and mutations.

Question 8

How disease-associated genes can be identified

Answer 8

GWAS (Genome-Wide Association Studies) identify genetic variants linked to diseases.
Polygenic Risk Scores sum risk alleles to predict disease susceptibility in complex traits.

Question 9

How understanding genes enables gene therapy design

Answer 9

SMA: Nusinersen promotes functional protein production.

CML: Imatinib blocks abnormal tyrosine kinase activity from the BCR-ABL fusion gene.