In this video, we're going to introduce nondisjunction. And so nondisjunction is an error that can occur during either meiosis 1 or meiosis 2, when chromosomes fail to separate from each other, which can result in aneuploid cells. Now aneuploid cells are cells that are going to contain either too many or too few chromosomes. And, again, aneuploid cells can be the result of a nondisjunction. Now nondisjunctions resulting in aneuploid cells can lead to genetic disorders. For example, trisomy 21 or Down syndrome, or it could even lead to cell death. And so let's take a look at our image down below which is showing you nondisjunction during anaphase 1 of meiosis 1 or, anaphase 2 of meiosis 2. And so notice, here at the top we're showing you a cell undergoing meiosis 1, and here at the bottom we're showing you a cell undergoing meiosis 2. And again, nondisjunction can occur either during meiosis 1 or meiosis 2 when these chromosomes are going to fail to separate properly. And so here what you can see is during metaphase 1 of meiosis 1, the homologous chromosomes are going to, randomly and, independently align themselves in 2 rows on the metaphase plate. And so what you'll see here is in this image, we're showing you the nondisjunction of a small blue chromosome. And so this small blue chromosome, if anaphase were to occur properly, it should shift over to this side of the cell. However, if a nondisjunction occurs of the small blue chromosome, notice that the small blue chromosome is actually going to go to the same side as its homologous chromosome pair. And so this side over here is going to be missing the homologous chromosome, whereas this side over here is going to have an additional homologous chromosome. And so what you'll notice is that this cell here, which would represent the cell here at the top, is going to have too many chromosomes. And so if you have too many chromosomes, that is going to be a type of aneuploid cell. And so notice that this cell over here only has one replicated chromosome, so it has too few chromosomes. And so you can see something similar occurring with meiosis 2 down below. And again in meiosis 2, the chromosomes all line up in 1 single file row. And this time, you can see that there's nondisjunction of the large red sister chromatids. And so, usually during, meiosis 2, this sister chromatid would go, to the bottom and the other sister chromatid would go to the top. But if there is nondisjunction, then notice that this bottom sister chromatid here is not going to separate. It's going to fail to separate. And so, notice that both sister chromatids would end up over in the same cell, and this cell would be lacking a sister chromatid. And so again, you would end up getting a cell that has too many chromosomes and a cell that has too few chromosomes. And so, again, if a cell has either too many or too few chromosomes, they're referred to as aneuploid cells. And again, this nondisjunction can lead to genetic disorders such as, again, trisomy 21 or Down syndrome. And trisomy 21, as you can see here, tri is a root that means 3, and, trisomy 21 is referring to having 3 copies of chromosome 21. And so if we take a look at this karyotype that we have over here on the right, notice that there are 2 pairs of every single chromosome except for this pair right here. And this pair, notice that there are actually 3 copies of this chromosome, chromosome 21, and that leads to, the genetic disorder trisomy 21 which is Down syndrome. And so we're showing you a baby here, cute baby with Down syndrome. And so, what you'll notice here is that, we have finished our lesson here introducing nondisjunction and how nondisjunction is an error that can occur during meiosis, where chromosomes or sister chromatids failed to separate resulting in aneuploid cells with either too many or too few chromosomes. And so we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.
Table of contents
- 1. Introduction to Biology2h 40m
- 2. Chemistry3h 40m
- 3. Water1h 26m
- 4. Biomolecules2h 23m
- 5. Cell Components2h 26m
- 6. The Membrane2h 31m
- 7. Energy and Metabolism2h 0m
- 8. Respiration2h 40m
- 9. Photosynthesis2h 49m
- 10. Cell Signaling59m
- 11. Cell Division2h 47m
- 12. Meiosis2h 0m
- 13. Mendelian Genetics4h 41m
- Introduction to Mendel's Experiments7m
- Genotype vs. Phenotype17m
- Punnett Squares13m
- Mendel's Experiments26m
- Mendel's Laws18m
- Monohybrid Crosses16m
- Test Crosses14m
- Dihybrid Crosses20m
- Punnett Square Probability26m
- Incomplete Dominance vs. Codominance20m
- Epistasis7m
- Non-Mendelian Genetics12m
- Pedigrees6m
- Autosomal Inheritance21m
- Sex-Linked Inheritance43m
- X-Inactivation9m
- 14. DNA Synthesis2h 27m
- 15. Gene Expression3h 20m
- 16. Regulation of Expression3h 31m
- Introduction to Regulation of Gene Expression13m
- Prokaryotic Gene Regulation via Operons27m
- The Lac Operon21m
- Glucose's Impact on Lac Operon25m
- The Trp Operon20m
- Review of the Lac Operon & Trp Operon11m
- Introduction to Eukaryotic Gene Regulation9m
- Eukaryotic Chromatin Modifications16m
- Eukaryotic Transcriptional Control22m
- Eukaryotic Post-Transcriptional Regulation28m
- Eukaryotic Post-Translational Regulation13m
- 17. Viruses37m
- 18. Biotechnology2h 58m
- 19. Genomics17m
- 20. Development1h 5m
- 21. Evolution3h 1m
- 22. Evolution of Populations3h 52m
- 23. Speciation1h 37m
- 24. History of Life on Earth2h 6m
- 25. Phylogeny2h 31m
- 26. Prokaryotes4h 59m
- 27. Protists1h 12m
- 28. Plants1h 22m
- 29. Fungi36m
- 30. Overview of Animals34m
- 31. Invertebrates1h 2m
- 32. Vertebrates50m
- 33. Plant Anatomy1h 3m
- 34. Vascular Plant Transport2m
- 35. Soil37m
- 36. Plant Reproduction47m
- 37. Plant Sensation and Response1h 9m
- 38. Animal Form and Function1h 19m
- 39. Digestive System10m
- 40. Circulatory System1h 57m
- 41. Immune System1h 12m
- 42. Osmoregulation and Excretion50m
- 43. Endocrine System4m
- 44. Animal Reproduction2m
- 45. Nervous System55m
- 46. Sensory Systems46m
- 47. Muscle Systems23m
- 48. Ecology3h 11m
- Introduction to Ecology20m
- Biogeography14m
- Earth's Climate Patterns50m
- Introduction to Terrestrial Biomes10m
- Terrestrial Biomes: Near Equator13m
- Terrestrial Biomes: Temperate Regions10m
- Terrestrial Biomes: Northern Regions15m
- Introduction to Aquatic Biomes27m
- Freshwater Aquatic Biomes14m
- Marine Aquatic Biomes13m
- 49. Animal Behavior28m
- 50. Population Ecology3h 41m
- Introduction to Population Ecology28m
- Population Sampling Methods23m
- Life History12m
- Population Demography17m
- Factors Limiting Population Growth14m
- Introduction to Population Growth Models22m
- Linear Population Growth6m
- Exponential Population Growth29m
- Logistic Population Growth32m
- r/K Selection10m
- The Human Population22m
- 51. Community Ecology2h 46m
- Introduction to Community Ecology2m
- Introduction to Community Interactions9m
- Community Interactions: Competition (-/-)38m
- Community Interactions: Exploitation (+/-)23m
- Community Interactions: Mutualism (+/+) & Commensalism (+/0)9m
- Community Structure35m
- Community Dynamics26m
- Geographic Impact on Communities21m
- 52. Ecosystems2h 36m
- 53. Conservation Biology24m
12. Meiosis
Genetic Variation During Meiosis
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Textbook Question
A wild-type fruit fly (heterozygous for gray body color and normal wings) is mated with a black fly with vestigial wings. The offspring have the following phenotypic distribution: wild-type, 778; black vestigial, 785; black normal, 158; gray vestigial, 162. What is the recombination frequency between these genes for body color and wing size? Is this consistent with the results of the experiment in Figure 15.9? Draw the chromosomes in the wild-type and black parents.
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Genetic Variation During Meiosis practice set
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