Genotype and Phenotype Flashcards
How does development start?
We begin life as just one cell at the time of fertilisation. This cell contains two sets of genes (one from mother and one from father). The genes are packaged into 46 protein parcels called chromosomes.
A single cell divides, and the genes are copied so that every cell possesses the full complement of genetic material. In the human body there are approximately 10 trillion cells!
What are genes made out of?
Constructed of a chemical called DNA (about 2 metres). There are 300,000 genes across our DNA.
How many chromosomes do we have?
23 pairs, the 23rd pair are sex chromosomes
What are autosomes?
The first 22 pairs of autosomes, which are not sex chromosomes
Genotype definition
- Genotype refers to the specific genetic make‐up of an individual, in the form of DNA
- The term was first used by Danish geneticist Wilhelm Johannsen (1857‐1927) to describe the entire genetic or hereditary constitution of an organism
Types of chromosomal abnormalities
- Deletion
- Duplication
- Inversion
- Substitution
- Translocation
Deletion
A chromosome has less genetic information than normal
Duplication
A chromosome has more genetic information than normal
Inversion
The order of genetic information on a chromosome is changed
Substitution
Information from one chromosome goes into another chromosome
Translocation
Two different chromosomes swap their information
Trisomies definition
The presence of a third copy of a chromosome
Trisomies examples
Down syndrome and Kleinfelter syndrome
Monosomies definition
The absence of one chromosome in the pair
Monosomies example
Turner syndrome - only one X chromosome
Cri du chat syndrome / 5Pminus syndrome
Missing chromosome 5, severe developmental delays with hyperactivity, aggression and repetitive movements. Found in 1 in 20k-50k newborns.
Phenotype definition
The observable expression of characteristics and traits coded for by genes
Genotype + environment = phenotype
Phenotypic traits include obvious observable traits
* Physical phenotype – height, weight, etc…
* Cognitive phenotype – language, executive ability etc…
* Social phenotype – friendly, distant, outgoing etc…
Genotype and phenotype are NOT directly correlated
Do genes effect phenotype?
Some genes only express a given phenotype in certain environmental conditions
Conversely, some phenotypes could be the result of multiple genotypes
Karmiloff-Smith, Scerif, and Thomas (2002)
“heritability figures based on monozygotic twins for autism and dyslexia are 60% and 65%
respectively … suggesting that environmental factors play an important role”
Differential susceptibility definition
Susceptibility to environment differs depending on genes involved in responsivity to the environment (plasticity genes)
Epigenetic definition
The study of phenotype changes that do not involve changes to the DNA sequence (e.g. they affect gene activity or gene expression)
Genomic method definition
Identify individuals with a known genetic disorder. Study those individuals to build up a phenotype / phenotypes associated with the disorder (eg behaviours / psychopathology)
Phenomic method definition
Identify behavioural phenotypes. Explore possibly underlying genetic causes (eg the study of the prevalence/characteristics within families)
Diagnosis definition
The identification of a disease, disorder, syndrome, condition etc.
When does diagnosis happen?
- For most disorders diagnosis occurs after birth and may result from queries from parents, teachers, observable features / behaviours, medical problems
- Diagnosis may follow lengthy assessments of behaviours/ cognition/ the collection of information from parents / teachers etc.
Prenatal diagnosis for Down syndrome name
Nuchal translucency scans
When and how are the scans for Down syndrome completed?
- Performed routinely weeks 11‐13
- Assesses the collection of fluid under the skin at the back of a baby’s neck
Amniocentesis - pre-natal test for down syndrome
- Under ultrasound guidance, a needle is inserted through the abdomen to remove a small amount of amniotic fluid.
- The cells from the fluid are then cultured and a karyotype analysis (an analysis of the chromosomal make‐up of the cells) is performed
How is Williams Syndrome assessed (name and what happens)
A type of specialized chromosome analysis using fluorescent markers
