Essential Cell Biology 5th edition

656 CHAPTER 19 Sexual Reproduction and Genetics
germ-line cell. Mitosis, in contrast, produces two genetically identical
diploid nuclei. Figure 19−6 summarizes the molecular events that distinguish
these two types of division—differences we now discuss in greater
detail, beginning with the meiosis-specific pairing of maternal and paternal
chromosomes.
(A) MEIOSIS
(B) MITOSIS
MEIOSIS II MEIOSIS I MEIOTIC S PHASE
diploid
germ-line
cell
paternal
homolog
maternal
homolog
CHROMOSOME
DUPLICATION
DUPLICATED HOMOLOGS
PAIR AND RECOMBINE
DUPLICATED HOMOLOG PAIRS
LINE UP ON THE METAPHASE SPINDLE
SEPARATION OF HOMOLOGS
AT ANAPHASE OF MEIOSIS I
COMPLETION OF MEIOSIS I
SEPARATION OF
SISTER CHROMATIDS
AT ANAPHASE OF MEIOSIS II
CHROMOSOME
DUPLICATION
diploid
cell
DUPLICATED
CHROMOSOMES
LINE UP INDIVIDUALLY
ON THE METAPHASE
SPINDLE
SEPARATION OF
SISTER CHROMATIDS
AT ANAPHASE
MITOTIC S PHASE
M PHASE
nonidentical haploid cells
genetically identical diploid cells
Figure 19−6 Meiosis generates four nonidentical haploid nuclei, whereas mitosis produces two identical diploid nuclei. As in Figure
19−3, only one pair of homologous chromosomes is shown. (A) In meiosis, chromosome duplication is followed by two meiotic divisions
to produce haploid nuclei. Each diploid nucleus that enters meiosis therefore produces four haploid nuclei, which are then packaged into
haploid gametes by specialized forms of cytokinesis. (B) In mitosis, each diploid nucleus produces two diploid nuclei, which are packaged
by cytokinesis into two diploid cells. Although ECB5 mitosis e19.07/19.06
and meiosis II are similar processes that are usually accomplished within hours,
meiosis I can last days, months, or even years, because of the time required for homolog pairing before meiosis I.