Overall Purpose of Meiosis: Meiosis is the process of cell division that reduces the chromosome number by half, resulting in the formation of four gametes (sperm or eggs) each with half the genetic material of the parent cell. This reduction is crucial for sexual reproduction, ensuring that offspring have the same chromosome number as their parents when fertilization occurs.

Process of Meiosis

1. Homologous Chromosomes: In meiosis, each chromosome from the parent pairs with its homologous chromosome. These homologous pairs align during the first meiotic division.

2. Tetrads: During prophase I, homologous chromosomes undergo synapsis, forming structures called tetrads, each consisting of four chromatids.

3. Crossing Over: This occurs during prophase I, where homologous chromosomes exchange genetic material, leading to genetic variation among gametes.

4. Reduction Division: Meiosis involves two rounds of division (meiosis I and II). In meiosis I, the homologous chromosomes are separated, reducing the diploid cell (2n) to two haploid cells (n). Meiosis II then separates the sister chromatids.

5. Sister Chromatids: After meiosis I, each chromosome still has two sister chromatids; these are separated in meiosis II, resulting in four haploid cells (gametes).

6. Haploid and Diploid: Diploid cells (2n) have two sets of chromosomes, while haploid cells (n) have one set.

Difference Between Meiosis in Males and Females

• In males, meiosis produces four functional sperm cells.

• In females, meiosis results in one functional egg and three polar bodies, which are non-functional cells that degenerate and do not participate in reproduction.

Three Main Ways Genetic Variation is Generated Through Meiosis

1. Independent Assortment: During metaphase I, the orientation of homologous chromosome pairs is random, which results in various combinations of chromosomes in the gametes.

2. Crossing Over: As described, this exchange of genetic material between homologous chromosomes increases variability.

3. Random Fertilization: The random union of sperm and egg during fertilization contributes to genetic diversity.

Compare and Contrast Mitosis and Meiosis

• Mitosis produces two identical daughter cells and is involved in growth and repair. It occurs in somatic cells.

• Meiosis produces four genetically diverse gametes, reduces the chromosome number, and is essential for sexual reproduction.

Differentiation of Vocabulary Words

• Haploid vs. Diploid:

  • Haploid (n): One set of chromosomes (e.g., gametes).

  • Diploid (2n): Two sets of chromosomes (e.g., somatic cells).

• 2n and n:

  • 2n: Represents diploid cells.

  • n: Represents haploid cells.

• Daughter Cells vs. Parent Cell: Daughter cells are the resulting cells from cell division, and the parent cell is the original cell.

• Somatic Cells vs. Gametes: Somatic cells are body cells (2n), while gametes are reproductive cells (n).

Define Terms in Embryo Development

• Fertilization: The union of sperm and egg, leading to the formation of a zygote.

• Embryo: The developing organism from fertilization until the end of the eighth week.

• Gamete: The reproductive cells (sperm and eggs).

• Zygote: The fertilized egg, the first stage of development after fertilization.

Role of Differentiation in Human Embryo DevelopmentDifferentiation is the process by which cells become specialized to perform specific functions. It begins shortly after fertilization as the embryo develops, leading to the formation of various cell types and tissues.

Stages in Embryo Development

1. Morula: A solid ball of cells resulting from division of the zygote.

2. Blastula: A hollow sphere of cells formed from the morula, leading to the next stage of development.

3. Gastrula: The stage where cell layers begin to form, giving rise to the primary germ layers.Stem cells present:

   • Morula: Totipotent stem cells (can form any cell type).

   • Blastula: Pluripotent stem cells (can form any cell type except for extra-embryonic tissues).

   • Gastrula: Multipotent stem cells (can form specific types of tissues).

Primary Germ Layers

• Ectoderm: Forms skin and nervous system.

• Mesoderm: Forms muscles, bones, and circulatory system.

• Endoderm: Forms the lining of internal organs.

• The primary germ layers develop during the gastrula stage.

Model of Differentiation Using Planaria: Planaria are flatworms known for their remarkable regenerative abilities. They have been used to study differentiation as they can regenerate entire body parts, providing insights into how stem cells can differentiate into various cell types and tissues.