Neurogenetics 1 Flashcards
How many chromosomes do we have?
46 chromosomes in total, have the same in every cell. This is carried in DNA. DNA helix is wrapped around protein (condensed tightly to DNA).
How is DNA structured?
Ladder structure – rungs of latter are pairs, and the way they bind together is specific. Have a genetic code which is a chain of letters of these nucleotide’s. When unravel this can see what the gene is encoding.
What is the relationship between genes and protein?
Approx. 23,000 genes on human chromosomes. Genes are long sequences of base pairs in the DNA that encode proteins. Can recgonise a gene by transcription factor – proteins that are able to bind to one specifc gene. Cascade of activity begins with transcription factors.
What happens in gene expression
The DNA partially unravels, allowing a transcription factor to bind to the gene. Transcription: In the nucleus, the gene’s DNA sequence is copied into messenger RNA (mRNA). Translation: A ribosome attaches to the mRNA and moves along the mRNA, reading each triplet codon (3 bases) and using transfer RNAs (tRNA) to put together the amino acid chain to make a protein. RNA signle rather than double stranded DNA, translated by ribosome’s. Ribosome looks at triplet codes and then makes a chain out of amino acids. This converts information in the DNA into functional proteins.
What happens in cell division (mitosis and meiosis)?
Your DNA in every cell should be identical. Gametes make genetic information that will be passed on to the next generation. Duplicate, line up together and a recombination occurs. This means when it divides instead of having identical chromosomes, will have a mixture of original parent and chromosomes. Gametes (egg cells of sperm cells) creates one half of chromosome so when combined it creates a chromosome pair. This is what gives us our individual difference.
What happens with genetic inheritance (meiosis)?
Homologous recombination or “crossing over”. Allows genetic diversity (natural selection and evolution). Offspring all share 50% of each parents genes, but a different 50%. Provides genetic diversity that allows us to deal with the envionrment and allows us to survive as a species.
What is Mendel’s law? (Mendelian Inheritance)
Gene is in one of two forms (known as
alleles) – either tall or dwarf. 2 copies of the gene in each parent pea. 1 copy is carried to each of the offspring. Height: Tall (T) is dominant. Dwarf (d) is recessive. If the genes are identical (TT or dd): homozygous
If the genes are not identical (Td): heterozygous.
What is an example of dominant inheritance?
Huntington’s chorea - movement, temperament and cognition. Autosomal dominant inheritance: single copy will be dominant and lead to the disease (if 1 parent has Huntington’s, 50% of the offspring will develop Huntington’s). Single gene disorder on chromosome 4. Due to an excessive repeat of CAG bases (normal chromosome has 11-34 copied, Huntington’s has excess of 40 copies). If one parent has it, 50% chance that the child will develop the mutated gene.
What is an example of recessive inheritance?
Phenylketonuria - caused by mutation in the PAH gene (phenylalanine hydroxlase). Gene encodes a protein. Function of the enzyme breaks down dietyr phenylalanime. If don’t break this down, get build up of amino acid and this is toxic to the developing brain and can result in a number of symptoms, e.g. epilepsy and learning difficulties. Recessive – need two bad copies to have this disorder. Can change the phenotype (two can have bad copies, but one person that has had a changed diet is going to show no abnormal phenotype). Same phenotype, but interplay of phenotype and environment can change consequence.
What is the result of chromosomal abnormalities?
Things going wrong during meiosis causing chromosomal abnormalities. Monosomy: single copy of a chromosome. Spontaneous abortion in early pregnancy. Trisomy: three copies of a chromosome. Very high rate of spontaneous abortions. Downs syndrome = trisomy in chromosome 21. If have trisomy of other chromosome pairs, this is so bad that the fetus doesn’t develop properly and results in miscarriage. Only because chromosome 21 has such minor effects can the fetus still develop.
What are x-linked conditions?
The wrong number of chromosomes impacts normal development reflecting importance of gene dosage e.g. Downs syndrome. But males have XY and females have XX, therefore major variation in gene dosage between sexes. Y chromosome - very few genes, mostly governing male sexual function. X chromosome - many genes that play vital roles in both sexes. Need to ensure that cells function normally with either one or two X chromosomes. X inactivation in females switches off one copy of X chromosome during embryogenesis. X-linked disorders vary in their penetrance according to sex. Half have maternal x active, half have paternal x active.
What is Rett syndrome?
X linked disorder. Progressive neurodevelopmental disorder almost exclusively affecting females, leading to profound mental impairment. Rare condition: 1in 10,000. Mutation in the gene MeCP2. This “transcriptional repressor” turns off the expression of unwanted genes during synapse formation. X-linked – gene on one copy of X chromosome (often spontaneous mutation rather than inherited). X – inactivation means that not all cells will express mutated MePC2 gene, therefore variable penetrance, sometimes see milder symptoms. (Affected males do not have a “good copy” of MePC2. Much severer phenotype, embryonic lethal or die soon after birth).
What is fragile X?
X-linked - most common inherited form of mental retardation. Relatively common: 1 in 4000 males, 1 in 6000 females. X-linked: symptoms predominantly in males.
