4. Genetic disorders Flashcards
What did Watson et al (1953) discover? (Disorders B&B)
- DNA double helix structure
- Made of 2 complementary chains of phosphate and deoxyribose
- 4 nucleotide bases
What are the four nucleotide bases? (Disorders B&B)
- Adenine
- Thymine
- Cytosine
- Guanine
What are genes? (Disorders B&B)
Long sequences of base pairs, in the DNA, that code for proteins
What are genes turned on by and what do they do? (Disorders B&B)
- Transcription factors
- Activated during development or by intracellular signalling cascades from other parts of the cell
What is gene expression? (Disorders B&B)
When a particular part of the DNA unravels to allow for a transcription fact to bind to the gene
What is transcription? (Disorders B&B)
In the nucleus, the DNA sequence is copied onto mRNA
What is translation? (Disorders B&B)
- Ribosome attaches to mRNA and moves long
- mRNA reads each triplet codon
- tRNA is used to make a chain out of the amino acids, creating a protein
What are the characteristics of mitosis? (Disorders B&B)
- Somatic cells (daughter cells identical to parents)
- Diploid
What are the characteristics of meiosis? (Disorders B&B)
- Gametes (daughter cells contain half the number of parent chromatids)
- Haploid
What is homologous recombination? (Disorders B&B)
- Crossing over in meiosis
- Allows for genetic diversity
- This is the basis of natural selection
What are the characteristics of Huntington’s Chorea? (Disorders B&B)
- Dominant inheritance
- Degeneration of the stratum (brain)
- Deterioration in movement, cognition and temperament
What causes Huntington’s Chorea? (Disorders B&B)
- Autosomal dominant inheritance
- Single gene disorder on chromosome 4
- Excessive repeat of CAG bases
What is autosomal dominant inheritance? (Disorders B&B)
A single copy will be dominant, leading to the disease i.e. if one parent has hunting tons, 50% chance the offspring will
What are the characteristics of Phenylketonuria? (Disorders B&B)
- Recessive inheritance
- Mutation on the PAH gene
- Build up of phenylalanine (toxic) leading to learning difficulties and epilepsy
What is the offspring probability of getting a recessive disorder, if both parents are carriers? (Disorders B&B)
- 25% chance offspring will suffer
- 50% chance offspring are carriers
What are the three types of prenatal chromosomal abnormalities? (Disorders B&B)
- Monosomy
- Trisomy
- Downs syndrome
What is monosomy? (Disorders B&B)
Single copy of a chromosome (one chromosome lacks the matching partner)
What is trisomy? (Disorders B&B)
Three copies of the chromosome (extra copy present)
What is Downs syndrome? (Disorders B&B)
Trisomy on chromosome 21, where there is an error in the first meiotic division
What is an X-linked condition? (Disorders B&B)
The gene causing the condition is located on the X chromosome
What is the Y chromosome important for? (Disorders B&B)
- Very few genes
- Mostly govern male sex function
What is the X chromosome important for? (Disorders B&B)
- Many genes
- Play a vital role in both sexes
What happens in female X-innactivation? (Disorders B&B)
One X copy is switched off randomly (allowing the body to function normally)
What are the characteristics of RETT syndrome? (Disorders B&B)
- Almost exclusively to females
- Leads to mental impairment
What are the causes of RETT syndrome? (Disorders B&B)
- Mutation in the MeCP₂ gene
- Transcriptional repressor turns off the expression of unwanted genes during synaptic formation
- Not all the cells express the mutated gene so symptoms vary (due to x-innactivation)
