Mitosis, Meiosis, Sexual and Asexual Reproduction

• Mitosis is a type of nuclear division yielding genetically identical cells.
• Mitosis functions in growth, tissue repair, cell replacement, and asexual reproduction.
• Meiosis is a type of nuclear division yielding genetically different cells.
• Meiosis is used to produce gametes (sex cells).

Sexual Reproduction

• Sexual reproduction involves the fusion of nuclei from two gametes (sex cells) to form a zygote (fertilized egg cell), producing genetically different offspring.
• Animal gametes include sperm and egg cells.
• Flowering plant gametes include pollen and egg cells.
• Fertilization is the fusion of gamete nuclei, where each gamete from a different parent contributes to variation in offspring.
• The formation of gametes involves meiosis.

Asexual Reproduction

• Asexual reproduction does not involve sex cells or fertilization.
• Only one parent is required, so there is no fusion of gametes or mixing of genetic information.
• Offspring are genetically identical to the parent and each other (clones).
• Asexual reproduction results in genetically identical offspring from one parent.
• Only mitosis is involved in asexual reproduction.

Meiosis

• Cells in reproductive organs divide by meiosis to form gametes (sex cells).
• The number of chromosomes must be halved when gametes are formed.
• Otherwise, the chromosome number would double after fertilization in the zygote (fertilized egg).
• Meiosis is a reduction division where the chromosome number is halved from diploid to haploid, resulting in genetically different cells.
• Meiosis starts with chromosomes doubling, similar to mitosis, and lining up in the center of the cell.
• Cells divide twice, so each gamete receives only one copy of each chromosome.
• Gametes are described as haploid, having half the normal number of chromosomes.
• Due to this double division, meiosis produces four haploid cells.

Chromosomes in Meiosis

• Chromosomes are paired with a maternal and paternal chromosome.
• A replicated chromosome has chromatids (one arm of replicated chromosome).
• Each chromosome is duplicated.
• The nuclear membrane breaks down and maternal and paternal chromosomes pair up along the center of the cell.
• Sections of DNA are swapped between maternal and paternal chromosome pairs, creating recombinant chromosomes.
• Chromosome pairs separate and move to opposite sides of the cell.
• This process is different from how chromosomes organize during mitosis.