gene structure and chromosomal abnormalities Flashcards
what makes up the human genome?
Genes - exons and introns
intergenic regions
small DNA molecule in mitochondria
how many bases in whole human genome?
3.2billion
what is a gene
the basic physical and functional unit of heredity
how many genes in human genome
20,000-23,000
makes up 2% of genome
introns
AKA intragenic regions
non-coding regions found within genes
intergenic regions
do not contain protein-coding sequences - between the genes
contain regulatory elements involved in switching genes on and off
mitochondrial DNA
circular double-stranded DNA molecule
codes for 37 genes
inherited exclusively from oocyte - maternal pattern of inheritance
what makes up chromatin?
DNA
RNA
protein
what is the main protein in chromatin?
histones
formation of chromatin
DNA wound around histones to form nucleosomes which are organised into solenoids.
Solenoids loop up into structure of chromatin
types of chromatin?
euchromatin
heterochromatin
euchromatin
open chromatin and prevalent in parts of genome being regularly used - where genes are switched on
heterochromatin
condensed for of chromatin made up of tight loops - most abundant in parts of the genome where genes are switched off
what do the light and dark stained parts represent on chromosomes?
light = open chromosome structure, euchromatin dark = condensed chromosome, heterochromatin
what is the p arm?
short arm structure of chromosome
what is the q arm?
long arm of chromosome
where is centromere located?
constricted point of chromosome, closer to top of chromosome
how many DNA molecules are there in a chromosome?
1
what introduces variation during meiosis?
crossing over
independent assortment
errors/ mutations in replication
DNA damage in germline cells
changes cause heritable defects
DNA damage in somatic cells
changes cause non-heritable local changes
when does crossing over occur?
1st meiotic division
mutations
drive evolution but can be pathogenic, causing disease
when does crossing over occur?
1st meiotic division - prophase 1
when does independent assortment occur?
before crossing over in first meiotic division
what happens in crossing over
homologous chromosomes exchange genetic material at chiasma
introduces genetic variation
which enzyme corrects mistakes by RNA polymerase?
MMR excision
what is MMR excision
goes along newly made strand and looks for mistakes in base pairing by RNA polymerase - wrong bases and corrects them
mismatch repair
what happens independent assortment?
during anaphase 1
centromeres do not duplicate and divide so only one member of each pair of chromosomes migrate to each daughter cell - either maternal or paternal
mix of chromosomes is different from cell to cell
what is loss or gain of a chromosome called?
aneuploidy
what is loss of a single chromosome
monosomy
gain of one homologous chromosome
trisomy
gain of 2 homologous chromosomes
tetrasomy
what is addition of one or more complete haploid components
polyploidy
turner syndrome
monosomy X
nullisomic gametes
missing chromosomes
result in monosomic zygote
disomic gametes
double no. chromosomes
results in trisomic zygote
banding
looking at band pattern of homologous chromosomes to see if they are the same
what is the most common trisomy?
16
symptoms of downs syndrome
learning disorder
issues with social skills
shorter
heart defects
