CHROMOSOMES AND CELL CYCLE
Haploid - having a single complete set of chromosomes, usually the number found in
gametes.
Diploid - having two complete sets of chromosomes, usually the number found in somatic
cells.
Homologous chromosomes - structurally similar chromosomes carrying the same genes
in the same order.
Genes are found at specific locations on chromosomes called loci.
Different forms of the same gene are called alleles.
Dominant alleles mask the effect of recessive alleles.
Chromosomes are linear in eukaryotes and circular in prokaryotes.
Linear chromosomes have centromeres. Replicated chromosomes have two chromatids
joined by a common centromere. When chromatids separate, they are considered
chromosomes.
CELL CYCLE
Interphase
First Gap Phase - most cell synthetic activities occur, cell growth.
Synthesis Phase - DNA replication, chromosomes are copied to form two
chromatids.
Second Gap Phase - cell prepares for division.
Mitosis
Prophase - nuclear membrane disaggregates, chromosomes condense.
Metaphase - replicated chromosomes align along equatorial plane of cell.
Anaphase - chromatids separate and move along spindle toward poles.
Once chromatids separate, they are considered chromosomes.
Telophase - chromosomes (formerly chromatids) are separated at opposite ends of
spindle, nuclear envelope re-forms around each set of chromosomes.
Cytokinesis physically divides cell into two.
Meiosis
Meiosis I - reduction division
prophase - homologous chromosomes pair up in process called synapsis.
Chromosomes form tetrads and cross over.
metaphase - homologous pairs of chromosomes align along equator.
anaphase - homologous chromosomes separate, reducing chromosome
complement by half (e.g. diploid to haploid).
telophase - single haploid set of replicated chromosomes are at either end
of spindle.
Meiosis II - equational division
prophase - replicated chromosomes condense.
metaphase - chromosomes align along cell equator.
anaphase - chromosomes split, separating chromatids.
telophase - chromosomes (chromatids) are at ends of spindle.