Chromosome Structure Reference
Meiosis Overview
Key Labels and Concepts
Chromosome Structure:
- Centromere: Point of attachment for spindle fibers; separates sister chromatids during Meiosis II / Mitosis
- Telomere: Protective end caps of chromosomes
- Homologs: Two chromosomes in a pair — one maternal, one paternal — each carrying alleles for the same genes
- Sister chromatids: Identical copies of one chromosome, joined at centromere after DNA replication
- Non-sister chromatids: Chromatids from different homologs — crossing over occurs here
Meiotic Stages Relevant to Inheritance:
| Stage | Event | Mendelian Law |
|---|---|---|
| Prophase I (pachytene) | Synapsis; chiasmata form; crossing over between non-sister chromatids | Basis for recombination |
| Metaphase I | Bivalents (tetrads) align at metaphase plate; each pair orients randomly | Law of Independent Assortment |
| Anaphase I | Homologs separate; allele pairs segregate | Law of Segregation |
| Anaphase II | Sister chromatids separate | Final production of haploid gametes |
Why Meiosis Produces 1:2:1 Genotypic Ratio
- Tt parent → Meiosis I separates T chromosome from t chromosome
- Meiosis II separates sister chromatids
- Gametes: 50% carry T allele, 50% carry t allele
- Random fertilisation of T and t gametes → 1 TT : 2 Tt : 1 tt