D3.2.1 Production of haploid gametes in parents Notes

Production of Haploid Gametes and Formation of a Diploid Zygote

1. In sexual reproduction, parents contribute half of their genetic material to offspring through gametes.
2. This ensures that the resulting zygote has the correct chromosome number:
   1. Gametes are Haploid: Each gamete contains one chromosome of each type (n), whether it comes from the male (sperm) or female (egg).
   2. Zygotes are Diploid: When male and female gametes fuse during fertilization, their chromosome number doubles, forming a zygote with two sets of chromosomes (2n).

Meiosis Creates Haploid Gametes

1. Parents halve the chromosome number of their body cells (diploid) to form haploid gametes through meiosis.
2. This process ensures the accurate distribution of genetic material to offspring.
   1. Diploid Cells Begin with Two Copies of Each Chromosome:
      For example, a diploid human cell has 46 chromosomes (23 pairs).
   2. Haploid Cells Have One Copy of Each Chromosome:
      Through meiosis, gametes are formed, each with 23 chromosomes in humans.

Fertilization Restores the Diploid Chromosome Number

1. When a sperm cell and an egg cell fuse:
   1. Their haploid nuclei combine, forming a diploid zygote.
   2. The zygote now contains two copies of each chromosome (one from each parent).

Why Haploidy and Diploidy are Important

1. Haploidy Prevents Doubling of Chromosome Numbers: Meiosis ensures that gametes contribute only one set of chromosomes, avoiding excessive chromosome numbers in offspring.
2. Diploidy Provides Genetic Redundancy: Each gene has two copies, one from each parent, allowing for greater genetic diversity and backup for harmful mutations.