Somatic vs Germ Cells: Understanding Cell Division
Somatic Cells and Germ Cells
Somatic cells: These cells make up the body tissues of a living organism. They divide by mitosis and always have two sets of chromosomes or genetic material (2n), making them diploid.
Germ cells: These cells merge with another cell to form a new sexual being. They divide by meiosis and only have one set of chromosomes (n), making them haploid cells.
Haploid and Diploid Cells
Number of chromosomes:
- Haploid: Contains half the normal number of chromosomes (23).
- Diploid: Contains twice the normal number of chromosomes (46).
Gamete chromosomes:
- Haploid: Have one set of chromosomes.
- Diploid: Have two sets of chromosomes.
Origin of chromosomes:
- Haploid: Chromosomes come from either a male or female gamete.
- Diploid: Chromosomes come from both a male and female gamete.
Genetic material:
- Haploid: Have half the genetic material.
- Diploid: Have the complete genetic material.
Products:
- Haploid: Products of meiosis.
- Diploid: Products of mitosis.
Oogenesis and Spermatogenesis
Spermatogenesis:
- Occurs in the testicles.
- Originates from a diploid cell called spermatogonia.
- Sperm are produced continuously throughout a man’s life.
- Continuous evolution.
- Produces a large quantity of sperm.
- Small amount of yolk or nutritious deutoplasm.
- Four sperm result from each spermatogonium.
- Plasma membrane.
Oogenesis:
- Occurs in the ovaries.
- Originates from an oogonium.
- A female is born with a certain number of eggs (around 400,000).
- Evolution with pauses (anestrus cycle).
- About 500 eggs are produced throughout the lifetime of the animal.
- Large amount of deutoplasm.
- One egg results from each oogonium; the other three cells degenerate.
- Complex of membranes.
Role of Mitosis and Meiosis
Mitosis: Produces two diploid cells from a diploid cell.
Meiosis: Produces four haploid cells from a diploid cell.
Differences Between Mitosis and Meiosis
In mitosis, the two daughter nuclei formed have the same number of chromosomes as the mother cell. In meiosis, the daughter cells have only half the number of chromosomes as the stem cell.
Meiosis involves the formation of male and female gametes with n chromosomes (haploid) from a diploid cell (2n chromosomes). Mitosis involves the formation of daughter cells with the same genetic information as the mother cell (diploid cells with 2n chromosomes).
Meiosis has twice as many phases as mitosis.
Homologous chromosome: Each pair of chromosomes that exist within the eukaryotic diploid body, matching each other during meiosis.
Karyokinesis: Ensures the maintenance of the genetic heritage of a species.
Cytokinesis: The physical separation of the cytoplasm into two daughter cells during cell division.
Monohybrid cross: When the differences between the properties being studied do not mix.
Dihybrid cross: A cross between two pure strains for two features.
Genotype: The genetic content (the specific genome) in an individual, in the form of DNA.
Phenotype: The expression of the genotype in a given environment.
Homozygote: When individuals contain only one type of character.
Heterozygotes: When individuals have both types of character.
Dominant character: Always appears in the first generation.
Recessive character: Appears in the second generation.
Characteristics of Drosophila
- Have giant chromosomes in the salivary glands.
- The female is larger than the male.
- The female has a pointed abdomen.
- Males have an oval abdomen.
- Small size, rapid life cycle, large numbers of offspring, easy to raise.
- Females have 5 disks in their abdomen, males have 3.