Chromosomal basis of inheritance

cell division – mitosis and meiosis

double helix

nucleosomes

chromosome (metaphase)

‘supercoil’

DNA is normally dispersed in cell; condensed prior to cell division

Location of DNA in cells:

Chromosomes

structure: two chromatids connected at the centromere

• 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

Chromosomes

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

equationaldivision

interphase prophase I metaphase I anaphase I

metaphase II anaphase II

telophase II

crossing-over

Meiosis – cell division with chromosome # reduction

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)

• each species has a characteristic set of chromosomesN = 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)

Chromosomes