Failure of chromosomes to separate in meiosis, producing gametes with extra or missing chromosomes.
Homologues fail to separate in meiosis I or sister chromatids in meiosis II, giving gametes with n+1 or n-1 chromosomes. Fertilisation then produces trisomy or monosomy.
Most autosomal aneuploidies are lethal in the embryo, except for chromosomes 13, 18 and 21.
Failure of chromosomes to separate in meiosis, producing gametes with extra or missing chromosomes.
Nondisjunction is one of the 54 topics in Genetics. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Turner and Klinefelter Syndromes, Down Syndrome, Karyotype.
Risk of Down syndrome increases with maternal age, from about 1 in 1500 at age 20 to 1 in 100 at 40.
Work through the Beginner topics in Genetics first, such as Heredity, Gene, Allele, then return to Nondisjunction. Intermediate topics assume the Beginner vocabulary.
The closest topics to Nondisjunction are Turner and Klinefelter Syndromes, Down Syndrome, Karyotype, Law of Segregation. Comparing them side by side is a good way to see how the ideas connect.
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Nondisjunction. To practise the whole of Genetics, use the Genetics quiz.
Nondisjunction: Failure of chromosomes to separate in meiosis, producing gametes with extra or missing chromosomes. Turner and Klinefelter Syndromes: Sex chromosome aneuploidies: Turner is XO and Klinefelter is XXY. Read both side by side and note what each one explains.
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Turner and Klinefelter Syndromes and explain the difference aloud. Finally, take the Genetics quiz and come back to this page for any question you miss.
Sex chromosome aneuploidies: Turner is XO and Klinefelter is XXY.
🧬 GeneticsA condition caused by an extra copy of chromosome 21, also called trisomy 21.
🧬 GeneticsAn organised picture of an individual's chromosomes arranged by size, used to detect abnormalities.
🧬 GeneticsThe two alleles for a trait separate during gamete formation so each gamete carries only one.
🧬 Genetics