human genome and chromosomes Flashcards
what phase does DNA replication occur in?
S phase
what is a karyotype?
complete set of chromosomes in a species
what is a kayogram?
an actual photograph of chromosomes arranged in homologous pairs
what phase are karyograms usually taken in?
metaphase - chromosomes condense
what is the short arm of the chromosome called?
the p arm
what is the long arm of the chromosome called?
the q arm
what are telomeres?
protective DNA and protein cap with repeating DNA which caps the end of the chromosome
what happens to telomeres over time?
they shorten
what does the centromere do?
keeps sister chromatids together
attaches to microtubules
repetitive DNA
what is the G light band
light band of the DNA
gene rich
GC rich
early replication
what is the G dark band?
gene poor
AT rich
late replicating
what are the autosomes
chromosomes 1-22
what are the sex chromosomes
chromosomes 23
what is the haploid chromosome number?
23
what is the diploid chormosome number?
46
define aneuploidy
an abnormal number of chromosomes
define pseduogene
non-functional copy of a gene
genes get duplicated and mutated
what is disomy?
two copies of a chromosome
what is polyploidy
gain one or more haploid sets of chromosomes
what is translocation?
when one part of a chromosome breaks off and joins onto another chromosome
what is a Robertsonian translocation?
two chromosomes joining at their centromere
what causes down’s syndrome?
trisomy 21
robertsonian translocation (extra chromosome 21)
mosaicism
give some features of downs syndrome
distinct facial expression muscle hypotonia congenital heart malformations lower IQ - learning difficulties distinct facial feature may have single palm crease
what causes Edwards syndrome?
trisomy 18
what are some features of Edwards syndrome?
clenched hands with overlapping fingers
distinct feet and facial paterns
what causes Patau syndrome?
trisomy 13
what causes Klinefelter’s syndrome?
extra X chromosome in males
XXY
what are features of Klinefelter’s?
infertility
poorly developed secondary sexual characteristics
tall
what causes Turner’s syndrome?
only 45 chromosomes
missing an X chromosome in females
what are some features of Turner’s syndrome?
dont have periods - primary amenorrhoea short poorly developed breasts low hairline congenital heart disease
name some methods of prenatal diagnosis
amniocentesis
chorionic villus sampling - testing placenta tissue
non-invasive techniques e.g. ultrasound
what is lyonisation?
X chromosome inactivation
why is lyonisation needed?
so that female somatic cells only have one function X chromosome
what are pseudoautosomal regions?
genes found on both X and Y regions
what is the Barr body?
inactivated X chromosome
what is the SRY?
sex determining region of the Y chromosome
what is g banding?
A technique where you take a metaphase spread of chromosome on a glass slide, add trypsin and digest away some of the proteins so you’re left with some reproducible bands
what are coding sequences?
encode proteins
what are non-coding sequences?
intergenic regions and introns
what are exons?
regions of genes that encode protein sequences
what are introns?
non-coding regions between the exons in a gene
what are control elements?
sequences like promoters and enhancers that regulate transcription.
what is a pseudogene?
non-functional copy of a gene; arises from gene duplication followed by deleterious mutation in one copy.
what is pre-mRNA?
first strand made after transcription
what is splicing?
the process by which the introns are removed to give rise to the mRNA sequence which then codes for the protein
what are features of Patau syndrome?
• Affects midline structures particularly: incomplete lobation of the brain, cleft lip, congenital heart disease
how is down’s syndrome tested for?
ultrasound imaging of nuchal translucency
11-14 weeks
