BackChromosome Transmission During Cell Division and Sexual Reproduction
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Chromosome Transmission During Cell Division and Sexual Reproduction
Types of Animal Cells
Animal cells can be classified based on their role in reproduction and chromosome content.
Somatic cells: These are body cells other than gametes (e.g., blood cells). They are typically diploid, containing two sets of chromosomes.
Germ cells: These are gametes (sperm and egg cells). They are haploid, containing a single set of chromosomes.
In humans, somatic cells have a total of 46 chromosomes (23 pairs), while gametes have 23 chromosomes.
Eukaryotic Chromosomes Are Inherited in Sets
Chromosomes in eukaryotic species are organized in sets. Each member of a pair is called a homolog. Homologous chromosomes:
Are nearly identical in size
Have the same banding pattern
Share the same centromere location
Contain the same genes, but not necessarily the same alleles
Homologous chromosomes form a homologous pair during cell division.
Homologous Chromosomes Have the Same Loci
The locus (plural: loci) is the physical location of a gene on a chromosome. Homologous chromosomes have the same loci for genes, but may carry different alleles.
Genotype types:
Homozygous for the dominant allele
Heterozygous
Homozygous for the recessive allele
Cell Division
Cell division is essential for both asexual reproduction and multicellularity. In multicellular organisms, all cells are derived from a single cell that has undergone repeated cell divisions. For example, humans start as a single fertilized egg and develop into adults with trillions of cells.
The Eukaryotic Cell Cycle
Eukaryotic cells destined to divide progress through a series of stages known as the cell cycle:
G1 phase: Cell grows and prepares for DNA replication.
S phase: DNA is replicated, resulting in sister chromatids joined at the centromere.
G2 phase: Cell prepares for mitosis.
M phase (Mitosis): Division of the nucleus and cytoplasm (cytokinesis) occurs.
Key Point: The cell cycle ensures that genetic material is accurately duplicated and distributed to daughter cells.
Diagram: The Eukaryotic Cell Cycle
Additional info: The diagram typically shows the cyclical progression through G1, S, G2, and M phases, with checkpoints ensuring proper completion of each stage before proceeding.
Summary Table: Diploid vs. Haploid Cells
Cell Type | Chromosome Number | Example |
|---|---|---|
Somatic (Diploid) | 2n (e.g., 46 in humans) | Blood cell |
Gamete (Haploid) | n (e.g., 23 in humans) | Sperm or egg cell |
