3.2 Chromosomes Flashcards
chromosomes of prokaryotic cells
- singular chromosome = only one copy of each gene
- coiled up in nucleoid region
- genes are needed for basic life processes
- chromosome is makes, no histones
- second copy is made before binary fission
plasmids in prokaryote bacteria
small extra DNA molecules
- small, circular, naked
- few genes that are not essential for cell function but might be helpful (eg. antibiotic resistance)
- not replicated at the same time as chromosome (cell can have many copies)
- can be transferred between prokaryotic cells
plasmids are also used…
by scientists to artificially transfer genes between species
audioradiography
- grown with thymine nucleotides with radioactive hydrogen isotope
- e. coli cells placed on dialysis membrane and lysed with enzymes
- cell contents applied to photgraphic emulsion palced in dark
- radioactive isotopes reacted with emultion making dark areas
- dark areas= presence of DNA
conclusion of cairn’s technique
- e.coli has single cirular chromosome
- provided evidence for semi conservative replication
eukaryotic chromosomes
- linear strands of dna in helix
- nucleosomes formed by wrapping dna around histones
- coiled into chromatin during interphsse
- supercoiled to form characteristic chromosome shape in mitosis
Eukaryotic cells possess…
multiple chromosomes with different genes
each chromosome carries….
a different set of genes in a specific order
chromosomes can vary by
- length (number of base pairs in dna molecule)
- position of the centromere
all individuals of a species…
have same chromosomes with same gene/locus
genome:
complete set of genetic info in organism
genomic size:
vary among organisms
proportion of DNA
that acts as functional genes is variable
homologous chromosomes
- same size and structure, same sequence of genes, may have different alleles for genes
- to interbreed two organisms must have homologous chromosome sets
- each chromosome type comes from the egg and otehr comes from the sperm to make homogolous pairs
- unless motehr gives x and father gives y (not homogolous)
diploids
- 2 homologous pairs
- 2 copies of each gene
- 46 chromosome in human
- somatic cell
haploids
- 1 chromosome
- 1 copy of each gene
- 23 chromosome in human
- gamete/sex cell
sexual reproduction
haploid sperm and egg cells fuse into fertilization to produce a diploid zygote, which divides in mitosis to form embryo
chromosome number is…
fundemental characteristic that defines a species
organisms with different numbers of chromosomes are…
unlikely to be able to interbreed successfully
chromosome number does not equal
complexity
number of chromosomes in a species is known as the
N number
chromosome number tends to be…
conserved across millions of years of evolution
in rare cases, chromosomes can…
fuse or split during evolution to change the chromosome number of species
sex determination
XX - female
XY- male
x chromosome
- large with centromeme in the center
- x carries many genes in non-homologous region that is not in Y chromosome
y chromosome
small with a centromere near the top
- SRY gene on Y leads to male development
eggs
produced by females and have XX chromosomes
sperms
produced by males and have XY chromosomes
karyogram
diagram or photgraph of the chromosomes present in a nucleus of eukaryote cell arranged in homologous pais of decreasing length
karyotype
property of the cell described by number and tyoe of chromosomes in nucleus
3 key features to identify chromosomes
- seen in metphase most clearly
- stains give chromosome distinctive banding pattrn
- micrograph arranges in size and bandin pattern
trisomy
having a third (extra) copy of a chromosome
monosomy
having only one (missing) copy of a chromosome
