Rucete ✏ Biology In a Nutshell
1. What Is Nondisjunction?
- Nondisjunction is the failure of chromosomes to separate properly during meiosis or mitosis.
- It leads to gametes or daughter cells with extra or missing chromosomes.
2. Nondisjunction in Meiosis
- Happens when:
- Two homologous chromosomes fail to separate during Meiosis I, or
- Two sister chromatids fail to separate during Meiosis II
- Results in abnormal gametes with an incorrect number of chromosomes
- Fertilization involving these gametes can lead to conditions like trisomy (e.g., Down syndrome) or monosomy
3. Nondisjunction in Mitosis
- Happens when sister chromatids fail to separate in somatic cell division
- Leads to daughter cells with unequal chromosome numbers
- Can result in genetic mosaicism (organism with cells of different genetic makeups)
4. Mosaicism
- A condition where an individual has two or more cell populations with different genetic compositions
- Caused by mitotic nondisjunction during early embryonic development
5. Polyploidy
- Caused by complete nondisjunction where all chromosomes fail to separate properly
- Produces gametes with twice the normal number of chromosomes
- Fertilization involving these gametes can lead to polyploid organisms
- Common in plants, rare and usually lethal in animals
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Biology in a nutshell