Lecture 38 Prof Duncan Shaw

Chromosomes and karyotypes Chromosomes are easily prepared from blood (and other) cells, and examined by microscope - a “karyotype” Normal human body cells (“somatic” cells) are DIPLOID: 23 pairs of chromosomes: Numbers 1-22 (autosomes) X and Y (sex chromosomes) XX in females, XY in males Germ cells (egg, sperm) have 23 chromosomes - HAPLOID

p (short arm) “petit” q (long arm) P arms of acrocentrics (13,14,15,21,22) have repeated ribosomal RNA genes

Mitosis Process of cell division in somatic cells 1 diploid cell 2 diploid cells Goes through several defined stages Chromosomes are passed on as exact copies without recombination (usually) “Segregation” is the process whereby one copy of each replicated chromosome goes to each daughter cell

Meiosis Process of cell division in germ cells, to produce eggs or sperm (gametes) Diploid cell haploid cells Goes through several defined stages Chromosomes are passed on as re-arranged copies due to recombination - creates genetic diversity

Oogenesis & spermatogenesis Oogenesis is the process of egg formation Spermatogenesis is the process of sperm formation Both go through several stages, with different timing in males than females Sperms go through more cell divisions than eggs do - more chance of mutation

Fertilisation 2 haploid cells (egg, sperm) form 1 diploid cell (the zygote) which develops into the embryo Whether sperm contained an X or Y chromosome determines if embryo is female or male Embryo contains an assortment of genes from each original parent - more genetic diversity Mitochondria (and their DNA) come only from mother via the egg - maternal inheritance