Week 5 - topic 3

Question 1

Twin studies

Answer 1

• Twin studies provide a powerful method for estimating the influence of heredity on particular traits
• > Compare Monozygotic (identical) and Dizygotic (fraternal) twins
• > Monozygotic twins have identical genotypes—that is, their chromosomes, and the genes they contain, are identical
• > Dizygotic twins have a genetic similarity of around 50%

Question 2

Twin studies and disorders

Answer 2

• If both twins are diagnosed with same condition, they are concordant
• If only one is diagnosed, they are discordant
• If a disorder has a strong genetic basis, the percentage of monozygotic twins who are concordant for the diagnosis will be higher than that for dizygotic twins.

Question 3

Adoption studies

Answer 3

• All behavioural traits are affected to some degree by hereditary factors, environmental factors (physical, social and biological), and an interaction between these factors
• Compare people adopted early in life with biological and adoptive family members
• If people strongly resemble biological parents, trait is probably influenced by genetic factors

Question 4

Chromoses, DNA and genes

Answer 4

• Organisms have cells which contain chromosomes
• Chromosomes consist of long strands of DNA which contain instructions for producing proteins, important for cellular functioning
• Gene = functional unit of the chromosome, which directs synthesis of one or more proteins

Question 5

Genomes and alleles

Answer 5

• Genome = Complete set of genes that compose DNA of particular species
• Mutations in genes occur over generations, so no two people have the same genetic information (apart from MZ twins)
• Allele = the particular form of an individual gene

Question 6

Genomic studies

Answer 6

Genomic studies attempt to determine the location in the genome of genes responsible for various physical and behavioural traits

Question 7

Linkage studies

Answer 7

• identify families whose members vary in a particular trait (e.g. presence/absence of Huntington’s Disease)
• Markers = sequences of DNA whose locations are already known
• Compare markers across members of the family

Question 8

Genomewide association studies

Answer 8

compare all or portions of the genomes of different individuals to determine whether differences in the people’s genomes correlate with the presence or absence of diseases (or other traits)

Question 9

Benefits of genome-wide association studies

Answer 9

• Identify novel variant-trait associations (e.g. anorexia nervosa, major depressive disorder) which might have important clinical applications.
• Lead to the discovery of novel biological mechanisms (e.g. GWAS discovered that autophagy (how cells degrade and recycle components) plays a role in Crohns’ disease).
• GWAS data is easy to share and publicly available data allows for further discoveries and advancement

Question 10

Limitations of genome-wide association studies

Answer 10

• GWAS usually only estimate a modest amount of the heritability of a given trait meaning it can have limited clinical predictive value.
• Correlation does not equal causation - GWAS do not necessarily pinpoint causal variants and genes