Multiple Choice
In which step does the chromatin begin to condense
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9. Mitosis and Meiosis
Mitosis
0:58 minutesProblem 1a
Textbook Question
How do we know that chromosomes exist in homologous pairs?
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Understand the concept of homologous chromosomes: Homologous chromosomes are pairs of chromosomes that have the same genes at the same loci but may have different alleles. One chromosome in the pair is inherited from the mother, and the other is inherited from the father.
Review evidence from karyotyping: Karyotyping is a technique where chromosomes are visualized under a microscope during metaphase of mitosis. In diploid organisms, chromosomes are observed in pairs of similar size, shape, and banding patterns, which supports the idea of homologous pairs.
Consider Mendel's laws of inheritance: Mendel's law of segregation states that alleles for a gene separate during gamete formation, which implies that chromosomes carrying these alleles must also exist in pairs to segregate during meiosis.
Examine meiosis: During meiosis I, homologous chromosomes pair up (synapsis) and then segregate into different cells. This pairing and separation process provides direct evidence that chromosomes exist in homologous pairs.
Analyze experimental evidence: Studies such as those involving Drosophila (fruit flies) and other model organisms have shown that specific traits are linked to specific chromosomes, and these chromosomes behave in pairs during cell division, further confirming the existence of homologous pairs.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Homologous Chromosomes
Homologous chromosomes are pairs of chromosomes in a diploid organism that have the same structure and gene sequence, one inherited from each parent. They carry genes for the same traits but may have different alleles. The presence of homologous pairs is crucial for processes like meiosis, where they align and exchange genetic material, contributing to genetic diversity.
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Karyotyping
Karyotyping is a laboratory technique that involves the visualization of an organism's complete set of chromosomes. By staining and arranging chromosomes based on size and shape, scientists can identify homologous pairs. This method provides evidence for the existence of homologous chromosomes, as it allows for the comparison of chromosome structures and numbers in a cell.
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Meiosis and Genetic Recombination
Meiosis is a specialized form of cell division that reduces the chromosome number by half, resulting in gametes. During meiosis, homologous chromosomes pair up and can undergo genetic recombination through crossing over. This process not only demonstrates the existence of homologous pairs but also highlights their role in increasing genetic variation in offspring.
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