Figure 21-4 Molecular Biology of the Cell (© Garland Science 2008)
Meiosis
the Greek word for diminution or lessening
Gametes Are Produced by Two Meiotic Cell Divisions
223=8.4m
Figure 21-13 Molecular Biology of the Cell (© Garland Science 2008)
Sexual Reproduction Gives Organisms a Competitive Advantage
A peacock displaying his elaborate tail. Meiosis Creates Genetic Diversity - Reshuffling of genes helps a species to survive The least fit male: Genetic trashcan?
Alberts • Johnson • Lewis • Raff • Roberts • Walter
Molecular Biology of the Cell
Fifth Edition
Chapter 21 Sexual Reproduction: Meiosis, Germ Cells, and Fertilization
Rearrangements of telomeres during prophase in developing bovine eggs.
엄마/아빠 염색체 조각 교환
Figure 21-6 Molecular Biology of the Cell (© Garland Science 2008)
Duplicated Homologs (and Sex Chromosomes) Pair During Early Prophase I
Haploid and diploid cells in the life cycles of some complex and simple eucaryotes.
The Haploid Phase in Higher Eucaryotes Is Brief
Gametes + specified diploid precursor cells
Figure 21-1 Molecular Biology of the Cell (© Garland Science 2008)
Scanning electron micrograph of an egg with many human sperm bound to its surface
유성생식은 diploid에서 Diploid: 2 sets of chromosomes Haploid Mitosis Meiosis
Figure 21-5 Molecular Biology of the Cell (© Garland Science 2008)
Duplicated Homologs (and Sex Chromosomes) Pair During Early Prophase I
Homolog alignment and crossing-over.
Copyright © Garland Science 2008
Sex is not absolutely necessary
A hydra from which two new organisms are budding(arrows)
Sex is not absolutely necessary. AsexualHaploid cells are different from one another and from the two haploid cells that formed the organism – Different set of autosomes – Genetic recombination ―crossing-over‖
No division Specialized for sexual fusion
Figure 21-3 Molecular Biology of the Cell (© Garland Science 2008)
Meiosis Creates Genetic Diversity
• Autosomes and sex chromosomes • Homologous chromosomes • Crucial feature of meiosis
Comparison of meiosis and mitotic cell division.
which the duplicated homologs rather than the sister chromatids are pulled apart and segregated
the sister chromatids are pulled apart
gametes—eggs (or ova), sperm (or spermatozoa), pollen, or spores. a fertilized egg, or zygote
Figure 21-2 Molecular Biology of the Cell (© Garland Science 2008)
Crossing-Over Enhances Genetic Reassortment
Two major contributions to the reassortment of genetic material that occurs in the production of gametes during meiosis.