diploid number for humans
2n
46
haploid number for humans
n
23
we cannot infer from the number of chromosomes (haploid number) of a species:
# of genes
organism size
complexity
chickens have __ as many chromosomes as humans
almost twice
chromosome number and arrangement can change over evolutionary time
human chromosome 2 is result of fusion bw two ancestral ape chromosomes
in euk, transmission of genetic material from one gen to another involves
mitosis and meiosis
mitosis leads to production of
2 daughter cells
each with same # chromosomes as parent cell
2n-->2n (in diploids)
meiosis leads to production of
gametes
each with half number of chromosomes
2n-->n
interphase is a ____ phase
non-division phase
cell cycle
alteration between division (mitosis) and non-division (interphase)
G0 stage "G zero
the quiescent stage
a quiescent cell is neither dividing nor preparing to divide, but may later re-enter the cell cycle
S phase
part on interphase
cell's DNA is replicated to produce two identical copies
during most of the cell cycle, DNA exists in an unfolded state known as
chromatin
in preparation for cell division, DNA is replicated and condensed into
chromosomes
1 chromosome can be defined as:
1 single DNA molecule (condensed)
2 sister chromatids joined by centromere
since mitosis occurs after DNA replication, each mitotic chromosomes contains
two identical DNA molecules
these are "sister chromatids
centromere
connects sister chromatids
where spindle fibers will attach to the chromosome during mitosis
centromere location
can vary between different chromosomes
structure of condensed mitotic chromosome
sister chromatids
centromere
p arm (top)
q arm (bottom)
chromosomes exist as ______ in diploid organism
homologous pairs
one homolog is "maternal" the other is "paternal
human karyotype
contains two of each chromosome (except X and Y)
homologous chromosomes carry the same ___ but may carry different ___
same genes
diff alleles
DNA replication produces
identical sister chromatids (for each chromosome)
a human cell just prior to mitosis contains __ chromosomes and __ chromatids
46 chromosomes
92 chromatids
interphase
not part of mitosis
chromosomes are extended and uncoiled, forming chromatin
cell spends most of its time here
DNA replication occurs during interphase (S phase)
prophase
chromosomes condense, sister chromatids are already attached at the centromere
nuclear envelope breaks down
centrioles migrate to opposite poles
(prometaphase and) metaphase
spindle fibers form
chromosomes align at metaphase plate
anaphase
centromeres split, sister chromatids separate (disjunction)
sister chromatids are now daughter chromosomes
daughter chromosomes migrate to opposite poles
telophase
daughter chromosomes arrive at opposite poles
cytokinesis (division of cytoplasm) occurs
chromosomes decondense and nuclear envelope re-forms