Chromosomal basis of inheritance cell division mitosis and

Chromosomal basis of inheritance cell division – mitosis and meiosis

double helix DNA is normally dispersed in cell; condensed prior to cell division nucleosomes ‘supercoil’ chromosome (metaphase)

Location of DNA in cells:

Chromosomes structure: two chromatids connected at the centromere

Chromosomes • each species has a characteristic set of chromosomes • individual chromosomes vary in size and shape • number and size is unrelated to complexity of organism karyotype

Mitosis – cell replication interphase prophase metaphase anaphase telophase

Mitosis – cell replication interphase: DNA replication occurs to produce double-chromatid chromosomes prophase: DNA condenses metaphase: chromosomes align in center of cell anaphase: chromatids separate, move toward opposite poles telophase: nuclear membranes reform; cell splits into two (cytokinesis)

Meiosis – cell division with chromosome # reductional division interphase prophase I metaphase I equational division anaphase I metaphase II anaphase II telophase II

Meiosis – cell division with chromosome # reduction crossing-over

Segregation of chromosomes Meiosis II

Oogenesis vs. spermatogenesis sperm – many, with small cellular investment mitochondria rarely transferred to zygote ova – few, with large cellular investment many mitochondria inherited

Oogenesis vs. spermatogenesis sperm – many, with small cellular investment mitochondria rarely transferred to zygote ova – few, with large cellular investment many mitochondria inherited (remember mitochondrial DNA? )

polar bodies (3)

Chromosomes • each species has a characteristic set of chromosomes N = number of unique chromosomes (haploid number) 2 N = number of chromosomes in somatic cells of diploid species • number and size of chromosomes is unrelated to complexity of organism (e. g. , nematode N varies from 1 to 48)