In the biological world, a wide range of reproductive modes and life cycles are recognized. Asexual organisms exist where no evidence of sexual reproduction is evident, while other species alternate between short periods of sexual reproduction and prolonged periods of asexual reproduction. In most diploid eukaryotes, however, sexual reproduction is the only natural mechanism that results in new members of a species. Orderly transmission of genetic units from parents to offspring, and thus any phenotypic variability, relies on the processes of segregation and independent assortment that occur during meiosis. Meiosis produces haploid gametes so that, following fertilization, the resulting offspring maintain the diploid number of chromosomes characteristic of their species. Thus, meiosis ensures genetic constancy within members of the same species.
- 5.1 Life Cycles Depend on Sexual Differentiation
- Chlamydomonas
- Maize (Zea mays)
- Caenorhabditis elegans
- 5.2 X and Y Chromosomes Were First Linked to Sex Determination Early in the 20th Century
- 5.3 The Y Chromosome Determines Maleness in Humans
- Klinefelter and Turner Syndromes
- 47,XXX Syndrome
- 47,XYY Condition
- Sexual Differentiation in Humans
- The Y Chromosome and Male Development
- 5.4 The Ratio of Males to Females in Humans Is Not 1.0
- 5.5 Dosage Compensation Prevents Excessive Expression of X-Linked Genes in Humans and Other Mammals
- Barr Bodies
- The Lyon Hypothesis
- The Mechanism of Inactivation
- 5.6 The Ratio of X Chromosomes to Sets of Autosomes Determines Sex in Drosophila
- 5.7 Temperature Variation Controls Sex Determination in Reptiles
