3 Chromosome transmission during
cell division and sexual reproduction
3.1 General features of chromosomes
Chromosomes= structures within living cells that contain the genetic material.
Genes physically located in chromosomes; each contains a very long DNA segment (genetic material)+
proteins (bound to DNA+ gives it an organized structure).
Chromatin= complex of DNA+ proteins that is found within eukaryotic chromosomes.
Prokaryotes= bacteria+ archaea; no membrane-bound nucleus.
Single circular chromosome in the nucleoid= darkly staining region that contains the genetic material of
mitochondria, chloroplasts/ bacteria.
Eukaryotes= contain membrane-bound nucleus (protists, fungi, plants, animals).
Organelles= specialized structure within a cell that is surrounded by a single/ double membrane.
Nucleus= membrane-bound organelle in eukaryotic cells where the chromosomes are found.
Some have their own DNA: mitochondria+ chloroplasts= extranuclear/ extrachromosomal DNA.
Eukaryotic chromosomes are examined cytologically to yield a karyotype
Somatic cell= any cell of the body except for gametes+ precursors to gametes.
Gamete= reproductive cell (usually haploid) that van unite with another reproductive cell to create a zygote;
sperm+ egg cells-> germ cells= gametes (sperm+ egg cells).
Process of producing a karyotype:
1. Sample of blood is taken+ treated with Colchicine to stimulate division centrifuged.
2. Supernatant discarded+ cell pellet suspended in a hypotonic solution; cells swell.
3. Sample centrifuged suspended in a fixative+ stained.
Eukaryotic chromosomes are inherited in sets
Most eukaryotic species are diploid/ have a diploid phase in their life cycle= contains 2 sets of chromosomes.
Homologs= structures that are like each other due to descent from a common ancestor.
E.g., 1 of the chromosomes in a pair of chromosomes or genes descended from a common gene.
Allele= alternative form of a specific gene.
Locus= physical location of a gene.
Homologous chromosomes: 99% identical but sequences not completely identical.
Slight differences in DNA sequences; provide the allelic differences in genes.
Doesn’t apply for sex chromosomes; differ in size+ genetic composition-> not homologous chromosomes.
3.2 Cell division
Purposes of cell division:
Asexual reproduction= doesn’t involve the union of gametes; preexisting cell divides to produce 2 new cells.
E.g., bacteria, amoeba, yeast.
Multicellularity= consisting of more than 1 cell
Bacteria reproduce asexually by binary fission (fig 3.4)
Binary fission= bacterial cell divides into 2 daughter cells; become separated by the formation of a septum.
Single parent produces offspring; genetically identical to one another+ to parents.
FtsZ= protein important in cell division; recruits other proteins to produce a new cell wall between the
daughter cells.
cell division and sexual reproduction
3.1 General features of chromosomes
Chromosomes= structures within living cells that contain the genetic material.
Genes physically located in chromosomes; each contains a very long DNA segment (genetic material)+
proteins (bound to DNA+ gives it an organized structure).
Chromatin= complex of DNA+ proteins that is found within eukaryotic chromosomes.
Prokaryotes= bacteria+ archaea; no membrane-bound nucleus.
Single circular chromosome in the nucleoid= darkly staining region that contains the genetic material of
mitochondria, chloroplasts/ bacteria.
Eukaryotes= contain membrane-bound nucleus (protists, fungi, plants, animals).
Organelles= specialized structure within a cell that is surrounded by a single/ double membrane.
Nucleus= membrane-bound organelle in eukaryotic cells where the chromosomes are found.
Some have their own DNA: mitochondria+ chloroplasts= extranuclear/ extrachromosomal DNA.
Eukaryotic chromosomes are examined cytologically to yield a karyotype
Somatic cell= any cell of the body except for gametes+ precursors to gametes.
Gamete= reproductive cell (usually haploid) that van unite with another reproductive cell to create a zygote;
sperm+ egg cells-> germ cells= gametes (sperm+ egg cells).
Process of producing a karyotype:
1. Sample of blood is taken+ treated with Colchicine to stimulate division centrifuged.
2. Supernatant discarded+ cell pellet suspended in a hypotonic solution; cells swell.
3. Sample centrifuged suspended in a fixative+ stained.
Eukaryotic chromosomes are inherited in sets
Most eukaryotic species are diploid/ have a diploid phase in their life cycle= contains 2 sets of chromosomes.
Homologs= structures that are like each other due to descent from a common ancestor.
E.g., 1 of the chromosomes in a pair of chromosomes or genes descended from a common gene.
Allele= alternative form of a specific gene.
Locus= physical location of a gene.
Homologous chromosomes: 99% identical but sequences not completely identical.
Slight differences in DNA sequences; provide the allelic differences in genes.
Doesn’t apply for sex chromosomes; differ in size+ genetic composition-> not homologous chromosomes.
3.2 Cell division
Purposes of cell division:
Asexual reproduction= doesn’t involve the union of gametes; preexisting cell divides to produce 2 new cells.
E.g., bacteria, amoeba, yeast.
Multicellularity= consisting of more than 1 cell
Bacteria reproduce asexually by binary fission (fig 3.4)
Binary fission= bacterial cell divides into 2 daughter cells; become separated by the formation of a septum.
Single parent produces offspring; genetically identical to one another+ to parents.
FtsZ= protein important in cell division; recruits other proteins to produce a new cell wall between the
daughter cells.
