Multiple Choice
Which of the following chromosomal mutations increases the amount of genetic material from only some chromosomes?
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6. Chromosomal Variation
Chromosomal Mutations: Aneuploidy
2:21 minutesProblem 1b
Textbook Question
How do we know that human aneuploidy for each of the 22 autosomes occurs at conception, even though most often human aneuploids do not survive embryonic or fetal development and thus are never observed at birth?
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Understand the concept of aneuploidy: Aneuploidy refers to the presence of an abnormal number of chromosomes in a cell. For humans, this means having more or fewer than the normal 46 chromosomes. Aneuploidy can occur due to errors in meiosis, such as nondisjunction, where chromosomes fail to separate properly.
Recognize the role of prenatal genetic testing: Techniques such as preimplantation genetic diagnosis (PGD), chorionic villus sampling (CVS), and amniocentesis allow researchers to detect chromosomal abnormalities in embryos or fetuses before birth. These methods provide evidence of aneuploidy occurring at conception.
Consider the use of molecular techniques: Advanced methods like fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH) can identify chromosomal abnormalities in early-stage embryos or miscarried fetal tissue, confirming that aneuploidy arises during conception or early development.
Acknowledge the study of spontaneous abortions: Researchers analyze the chromosomal composition of miscarried embryos and fetuses. Studies show that a significant proportion of spontaneous abortions are due to aneuploidy, indicating that these abnormalities occur at conception but often lead to non-viable pregnancies.
Understand the role of meiotic studies: Observations of meiotic errors in gametes (sperm and egg cells) provide direct evidence of how aneuploidy arises. For example, nondisjunction during meiosis I or II can result in gametes with an abnormal number of chromosomes, which, upon fertilization, leads to aneuploid embryos.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Aneuploidy
Aneuploidy refers to the presence of an abnormal number of chromosomes in a cell, which can result from nondisjunction during meiosis. This condition can lead to various genetic disorders, depending on which chromosomes are affected. In humans, aneuploidy is most commonly associated with conditions like Down syndrome, which is caused by an extra copy of chromosome 21.
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Chromosomal Mutations
Chromosomal mutations involve changes in the structure or number of chromosomes, which can occur through mechanisms such as deletion, duplication, inversion, or translocation. These mutations can significantly impact gene expression and lead to developmental abnormalities. Understanding these mutations is crucial for studying genetic disorders and their inheritance patterns.
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Embryonic Development and Survival
Most aneuploid embryos do not survive to term due to the severe developmental challenges posed by chromosomal imbalances. However, early detection methods, such as preimplantation genetic diagnosis and prenatal screening, have shown that aneuploidy can be present at conception. This highlights the importance of understanding the early stages of embryonic development and the factors that influence survival rates of embryos with chromosomal abnormalities.
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