Sex cells have one set of chromosomes; body cells have two. Take
a look at human chromosomes. HI! Let's look at human
chromosomes. This is a photomicrograph of stained human
chromosomes from one body cell. How many chromosomes are there?
92. No, count again. 23. No, try again. These are the broken
pieces of one long chromosome. No, Walther Flemming did think
that chromosomes exist as one long piece that broke up during
mitosis, but this is not true. 46. That is correct. Human cells
normally have 46 chromosomes; this is the diploid number.
Chromosomes are usually arranged in a karyotype, where homologs
are shown side by side. This is useful for identifying some
human disorders. In this karyotype, how many pairs of
chromosomes are there? 46. No, try again. 23. That is correct.
Humans have 23 pairs of homologous chromosomes. How many of
these chromosomes will be found in an egg cell? All 46
chromosomes. No, sex cells have a half set of chromosomes. 23,
one from each pair. That is correct. 23, pairs 1-11 and one