Genetics in psychology Flashcards
Karyotype
Number form and size of chromosomes
p
Short arm of a chromosome
q
Long arm of a chromosome
Genotype
Describes our genetic makeup
Phenotype
Describes the observable characteristics that are joined to genetic makeup and environment
X-linked disorder
A disorder resulting from a genetic abnormality on the X chromosome. e.g. Fragile X syndrome which is dominant, X-linked disorder
Dominant disorder
A single copy of one abnormal gene is sufficient to cause a genetic condition – 50% risk of inheriting the gene for the disorder e.g. Huntington’s Disease
Recessive disorder
Two copies of the abnormal gene are needed to produce the disorder (so both parents must be carriers with one copy each) - 25% risk of inheriting the gene for the disorder e.g. Cystic fibrosis
Gender effects of X-linked disorders
Generally the heritability of x-linked disorders is greater for boys because, unlike girls, the have no second unaffected X chromosome as a ‘back up’. There is a ‘buffering’ effect in girls
Complexities in the effects of inherited genetic disorders
- Gene-gene interactions
- Gene protein levels
- Inherited set of unaffected genes & their impact
- Environmental factors
Allele
Variant form of a given gene
Heterozygous genotype
Describes a genotype with different alleles
Homozygous genotype
Describes a genotype with the same alleles
Fragile-X syndrome
World most common caused of inherited mental retardation. Cause of developmental delay, inhibitory control, repetitive speech. Only gene disorder known to cause autism.
Silencing of fMR1 gene causes the loss of the FMRP protein, resulting in Fragile-X phenotype.
X-linked, dominant gene disorder (50% chance of passing on)
Occurs in 2 stages dependent on number of CCG repeats. Large expansion [over 200] = fully affected, OR medium expansion [>55 repeats] = carrier. Carrier males can only pass on the medium expansion
Behavioural phenotype
Observable characteristics that occur more often in individuals with a specific genetic syndrome than individuals without that syndrome.
Williams syndrome
Rare neurodevelopmental disorder occurring in 1/7,500 to 20,000 births
Occurs from a micro-deletion of approx. 28 genes on long arm of Chromosome (7q11.23)
Missing the gene elastin, which results in disorders of the circulatory system and heart
Distinct facial phenotype (small upturned nose, wide mouth and spaced teeth, full lips)
Characterised by problems with visual-spatial and motor skills and attention skills. Hypersociability early, but heightened levels of generalised anxiety in later years, , unusual attraction to faces and affinity for music.
ADHD
Neurodevelopmental disorder that generally becomes apparent in the preschool and early school years and affects boys and girls. Affects about 5% of children (3 males to 1 female) and 4% of adults (1:1 m:f)
Believed to be linked to dopamine deficieny and often treated with Ritalin
Characterised by poor attention to detail, difficulties in maintaining attention over a sustained period of time, moment-to-moment variability throughout task performance
Inattentiveness is consistent across ages, however impulsivity and hyperactivity are considered to reduce with age.
Neuroimaging demonstrates problems in frontal lobe (attention), parietal lobe (visual-spatial information) and cerebellum (timing and coordination)
ADHD is considered 75-90% heritable
Candidate gene approach
Approach that selects genes of interest based upon knowledge of the disorder
Dopamine
An important neurotransmitter that is produced in many parts of the brain and plays a critical role in reward, cognition and emotion
