Neurgenetics Flashcards
How many pairs of chromosomes do humans have?
23
What is the structure of DNA?
a double helix consisting of 2 chains of phosphate and deoxyribose
What are the 4 nucleotide bases?
adenine, thymine, guanine and cytosine
What are the bonds between nucleotides?
a weak hydrogen bond
T-A and C-G
What are genes?
long sequences of base pairs in the DNA that encode proteins
How are genes activated?
by a transcription factors
What happens when a gene is activated?
the gene is transcribed into messenger RNA
How does a transcription factor work?
DNA partially unravels allowing the transcription factor to bind to the gene
What is transcription?
the genes on a DNA sequence are copied into mRNA
What is translation?
mRNA coding for an amino acid
What happens during translation?
a ribosome attaches to mRNA and reads each triplet codon
What is mitosis?
cell division creating somatic cells
What are somatic cells?
cells which are identical to the parent cell
What is meiosis?
cell division creating gametes
What are gametes?
cells which contain half the number of chromosomes as the parent cell
What happens during meiosis?
when the chromosomes have duplicated chiasma takes place and the DNA of the parent chromosomes is mixed up
What is the outcome of meiosis?
genetic diversity and offspring sharing 50% of DNA with parents (but a different 50%)
What is it called when the DNA gets mixed up during meiosis?
homologous recombination
What is a dichotomous trait?
one that only has two outcomes (no in between e.g. tall or short)
What are homozygous genes?
identical genes
What are heterozygous genes?
non-identical genes
What is Mendel’s Law?
genes can be either dominant or recessive
What is a dominant gene?
one that is carried AND expressed
What is a recessive gene?
on the is carried but NOT expressed
What is an allele?
a version of a particular gene
What is Huntington’s Chorea?
degeneration of the brain (striatum) leading to progressive deterioration of movement, temperament and cognition
How is Huntington’s Chorea inherited?
autosomal dominant inheritance; a single copy will be dominant and lead to the disease
What genetic mutation is associated with Huntington’s Chorea?
An excessive repetition of CAG bases, normal has 11-34, a Huntington’s chromosome has excess of 40
What is Phenylketonuria?
defect of an enzyme causing phenylalanine not to be broken down leading to learning disabilities, behavioural difficulties and epilepsy
How is Phenylketonuria inherited?
recessively; both parents must be carriers to get the disease
What is monosomy?
only one copy of chromosome is made leading to an early spontaneous abortion
What is trisomy?
three copies of a chromosome are made leading to a very high rate of spontaneous abortion
What can be caused by a trisomy of chromosome 21?
Down’s Syndrome, an over expression of certain genes causes symptoms
Why does trisomy occur?
due to an error in the first meiotic division
What does the Y chromosome code for?
Few genes but mostly governing male sexual function
What is Rett Syndrome?
a progressive neurodevelopment disorder leading to profound mental impairment only affecting women
What is Fragile X?
an inherited form of mental retardation most prevalent in males
What causes Fragile X?
an excessive repeated of CGG
When does X inactivation take place?
during embryogenesis
What are epigenetics?
changes in an organism due to the expression of a gene rather than the genetic code itself
What is genomic imprinting?
the silencing of a gene based on which parents gene is imprinted
How are genes switched of?
methylation of DNA which makes it harder to unravel for transcription
Is genetic imprinting passed on to the next generation?
Not always as it is reversible
How can a silenced paternal gene become active in the next generation?
if it is inherited maternally then the silencing is switched off
Which genes are active if paternal genes are imprinted?
maternal genes
Which genes are active if maternal genes are imprinted?
paternal genes
Where does genomic imprinting take place?
chromosome 15 between 4-5 million base pairs
When can spontaneous deletion of part of a chromosome take place?
during meiosis
What causes Prader-Willi syndrome?
the combination of paternal chromosome deletion and maternal imprinting
What is Prader-Willi syndrome?
intellectual disability, decreased muscle tone, short stature, emotional lability and insatiable appetite
What causes Angelman syndrome?
the combination of maternal chromosome deletion and paternal imprinting
What is Angelman syndrome?
delayed development, severe language impairment, movement and balance problems, epilepsy, small head, sociable behaviour and frequent smiling
What effect on gene expression can maternal care have?
maternal care switches on serotonin which affects the expression of the glucocorticoid receptor
What has an absence of maternal care been shown to cause in rats?
methylation of promoters, low levels of glucocorticoid receptor, high corticosterone levels and high anxiety
What evidence is there for transgenerational epigenetics?
parental environment can disrupt histones in sperm cells leading to an altered RNA profile in offspring and grand offspring
