Download Chromosomal basis of inheritance cell division – mitosis and meiosis

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 # reduction
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 I
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)
2N = 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)