Topic 11: Chromosomes Flashcards
how many chromsomes do humans have
46, 23 pairs
22 autosomal, 1 sex linked
female - XX, men - XY
what is the chromosome structure
2 chromatids
one chromatid - long molecule, lots of solenoid loopds, beads on string combined, histone core wrapped around dna
one chromosome before replication
one double stranded dna molecule
one chromosome after replication
two double stranded dna molecules
two sister chromatids joined by centromere
each sister chromatid consists of a p(short) and q(long) arm
what is a centromere
consists of repetitive seqeunces and links the chromatids
metacentric = p and q equal
submetacentric = p arm shorter than q
acrocentric = p arm almost non existent
telocentric = no p arm, only q arm with centromere
what are telomeres
repeating sequences on each end of chromosome, or on each chromatid after replication
TTAGGG
what are we looking at when we looking at ‘metaphase spreads’
actively diving cells
condensed chromosomes but stop growth of chromosomes in metaphase
stain chromosomes
banding pattern is formed
dark = AT rich, light = GC
karyotype = lines chromosomes up depending on homologous forms
what are ideograms
diagrams with specific banding for each of the chromosomes
centromeres lined up
used in online programmes
how does karyotype line up chromosomes
homologous chromosomes lined up in order of size or where centromere is
sister chromatids are
on the same chromosome
non-sister chromatids, are one chromatid from each homologous chromosomes
what are homologous chromosomes
same DNA sequence
have same genes located on them
genes may be different variants (alleles)
sister chromatids have identical DNA (as undergone replication) so same alleles
non sister chromatids have same genes, but different alleles (as paternal and maternal copy of genes not the same)
where are the chromosomes during interphase
in chromosome territories
in cell nucleus, chromosomes have different positions
