Human genetic in psy Flashcards
Phenotype
•Observable properties of an organism produced by the genotype and environmental influences
Down syndrome phenotype
–Sloping forehead –Protruding tongue –Short stubby limbs –Slightly flattened nose –Almond-shaped eyes –May have congenital eye, ear and heart defects
Chromosomes
•Most of our cells contain 46 chromosomes
•The 46 chromosomes are actually 23 pairs
–1 set from mother, 1 set from father
–except gametes: each contain only 23 chromosomes
–Gametes are the sex cells - sperm from male and ova from female
•Each chromosome pair carries genes of the same type
•These chromosome pairs match in size and the functions they serve
Karyotype
- The karyotype is a description of the chromosomal content of a cell
- The autosomes (non-sex chromosomes) are numbered 1 to 22
- The sex chromosomes are either X or Y
Variations in karyotype
47, X Y + 21 Down (cause mild to severe intellectual disability and physical abnormality) treat by surgery, specila intervention and education program. at 20, 1/1900, at 35 1/300 at 45 1/30
47, X X + 21 Down
47, X X Y Klinfer Extra X chromosome cause physical abnormality, treat by hormone therapy. one in 600
45, X Turner cause severe hormonal and intellectual issue, hormone therapy, 1/2500 female
47, X Y Y sydrome above averageheight, no treatment, 1/1000
Klinefelter syndrome
•XXY condition can affect development in 3 ways:
–Physical development: weak muscles and reduced strength. Lagging in physical development.
–Language development: Between 25 and 85% of XXY males have some language difficulties
–Social development: XXY males tend to be quieter and undemanding compared with XY males
Chromosomes role
- A chromosome carries the genetic information of the body
- Information is arranged in a linear sequence
- Chromosomes are made up of chromatin. Chromatin constitutes nucleic acids (DNA and RNA) and proteins (histones and non-histones)
- Chromosomes are only visible during cell division processes, called mitosis and meiosis. Otherwise, they unfold and uncoil into a diffuse network within the nucleus
Deoxyribonucleic acid
DNA
- Primary structure (sequence) of DNA is described by the order of the bases in a 5’ to 3’ direction
- Humans have ~ 3.3 x 109 bases
- The locus is used to describe a sequence of DNA situated on a specific region on a chromosome
- DNA is a double-stranded structure consisting of 2 nucleotides held together by hydrogen bonds between the bases in opposing strands
- DNA molecules are organized into stretches of sequence called genes
Genes
•Each gene has one or more specific effects upon the phenotype of the
organism.
•A gene can recombine with another gene
•A gene can mutate into different forms
•Genes are expressed at different time points in life
•A gene can only influence development when it is turned on and is
expressed
•For the DNA to impart information, it must first be transcribed
Transcription and
Translation
- The strand of DNA acts as a template for the synthesis of ribonucleic acid (RNA)
- Like DNA, RNA forms stable structures by base-pairing
- DNA information can be copied to RNA for transcription and translation and carried to other areas of the cell to create proteins
- Messenger RNA carries the instructions specifying sequences of amino acids
- Groups of three bases of mRNA serially code for each amino acid
- These groups of 3 bases are called codons
- There are potentially 64 possible codons, but in nature there are only 20 different amino acids
Areas of DNA
ORF: open reading frame
UTR: un-translated region
RBS: ribosome binding site
Promoter: region of DNA that initiates transcription of the gene
Operon: is a functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter
Polycistronic: codes for more than one protein
Proteins`
•20 different amino acids •Proteins are the end product of gene expression •Protein types: –Enzymes –Haemoglobin –Insulin –Collagen –Keratin –Histones –Actin and myosin –Immunoglobulins
Alleles
- About one-third of human genes have two or more different forms, called alleles
- An allele is one of two or more forms (or variations) of a gene
- The alleles of a given gene influence the same trait or characteristic
- E.g. eye colour
- The different allele forms result in different eye colours (green, brown, hazel, grey etc)
Gene Expression
- The dominant allele is the form of the gene that is expressed if present.
- The recessive allele is expressed if a dominant allele is absent.
Polygenic Inheritance
•When traits are governed by more than one
gene
•Applies to most traits and behaviors of interest
to behavioral scientists
Mutations
•Mutation is the process of change in the sequence of DNA
•Mutations are the source of genetic variation and the basis for natural selection
•Mutations have a wide range of effects on organisms, depending on the type and location of mutation
•They can occur spontaneously or be induced by external factors such as exposure to chemicals and radiation
•There are four main types of mutations
–Base substitutions
–Deletions of DNA
–Insertions of DNA
–Whole or partial chromosomal abnormalities
Genetic origins of disease
•Over 5,000 human diseases and disorders are mpresently known to have genetic origins
Recessive gene: PKU, sickle-cell anemia, Tay-Sachs mdisease, cystic fibrosis
Single dominant gene: Huntington’s disease, neurofibromatosis
Polygenic inheritance: cancer, heart disease, asthma, mpsychiatric disorders, behavior disorders
Sex-Linked inheritance: red-green color blindness, hemophilia, Duchenne muscular dystrophy, fragile-X syndrome
Chromosomal anomalies: Down syndrome (trisomy 21), Klinefelter syndrome (XXY), Turner syndrome (XO)
Regulator gene defects: genetic male with female genitalia
Tay-Sachs disease
- A fatal, autosomal recessive neurodegenerative disease of infancy and early childhood
- Rare in most populations
- Caused by mutations of HEXA gene on chromosome 15q23-q24.
- First identified in 1969
Tay-Sachs disease vunerable pop
•Population studies and pedigree analyses suggest that mutations may have arisen from small founder populations:
–Carrier frequency is 1:25 in Ashkenazi Jews
–Same mutation is found in Cajun population in southern Louisiana
–Two different mutations are common in French Canadians
–Higher carrier frequency in Irish-American and Pennsylvania Dutch communities compared with general population
•Incidence in unscreened Jewish populations is 1 in 3,900 births
•Internationally, screening has reduced the incidence of Ashkenazi Jews with TSD-affected children by more than 90%
Tay-Sachs disease education in australia
•Australian high-school-based preconception genetic screening programs help young people through screening and education
–Choosing a partner not at risk
–IVF, donor gametes, adoption
–Selective terminations
–Child-free
•Aim is to optimize reproductive and life choices for participants.
Huntington’s disease
- Progressive neurodegenerative disorder
- Autosomal dominant
- Huntington gene isolated in 1993, on chromosome 4 at 4p16.3
- > 40 repeats of CAG (cytosine, adenine, guanine) trinucleotide in coding region of gene
- Mean onset ~40 yrs, death 12-15 years afterwards
- Prevalence 5-10 per 100,000 people
- Symptoms include cognitive deterioration, personality change, memory loss and depression, and choreic and slow movement
- The gene contains an expanded trinucleotide repeat (CAG) that ranges from 9-35 in healthy adults, and from 36 to 180 in Huntington’s disease.
- Alleles with 36-39 repeats show “reduced penetrance”- only some individuals will go on to develop clinical symptoms.
- Individuals with juvenile-onset (Westphal variant) usually have expansions >55 repeats and develop Huntington’s disease before 20 years.
- Onset appears to be earlier when the transmission is from the father.
Chorea and bradykinesia
characterise movement
control in HD
Voluntary
• Bradykinetic
• Inconsistent and inefficient movement
-Abnormal co-contractions of muscles
-Prolonged EMG bursts
-Less efficient and more variable movements in handwriting
• Sequential and simultaneous movement difficulties
Involuntary
• Involuntary ‘dance-like’ choreic movement
• Abates in advance stages of disease, when akinetic and mbradykinetic movements become mclearer
Broad sub-cortical and cortical damage in HD
- Neuronal and astrocyte loss in the basal ganglia (caudate, putamen, global pallidus and other areas)
- Selective degeneration of GABAergic neurons of striatum
- As disease progresses, greater cortical atrophy occurs
Schizophrenia
•Fundamental and characteristic distortions of thinking, perception and affect that are inappropriate or blunted
•Psychopathological thoughts
–Hallucinations, paranoid or bizarre delusions, and disorganised speech and thinking leading to significant social and occupational dysfunction
•Onset typically occurs in young adulthood
•Affects ~ 0.5% of population
•Course of schizophrenic disorders can be continuous or episodic
•Not due to depression or manic symptoms unless it is clear that schizophrenic symptoms antedate the affective disturbance; not due to drug intoxication or withdrawal