Question

Part IV – Chromosomes and Cell Division Dan and Annie understand that the cause of their deafblindness lies in their chromosomes and runs in their families. Like most humans, they have 23 pairs of chromosomes in the nucleus of all their somatic (body) cells, which can be visualized in a karyotype, a set of photographs of a single cell’s chromosomes taken with a microscope (Figure 9). These cells are rapidly dividing epithelial cells, therefore many cells will be in a stage of mitosis in which the chromosomes are condensed (late prophase or early metaphase) and therefore easy to see. The technician fixes cells onto a slide, squashes and stains them, then uses imaging software to digitally cut out the chromosomes and line them up by size, largest to smallest. Figure 9. Human karyotype. Credit: National Human Genome Research Institute, PD, <https://en.wikipedia.org/wiki/File:Human_male_karyotpe.gif>. Questions 1. Each of the 46 chromosomes shown here is already replicated, therefore each chromosome in a karyotype is composed of two identical sister chromatids. The two strands of the ‘‘X’’ are tightly attached at a centromere and along the length of the chromatids. Knowing this, how many molecules of DNA are shown in this karyotype? (each double helix is considered one DNA molecule).

          Part IV – Chromosomes and Cell Division

Dan and Annie understand that the cause of their deafblindness lies in their chromosomes and runs in their families. Like most humans, they have 23 pairs of chromosomes in the nucleus of all their somatic (body) cells, which can be visualized in a karyotype, a set of photographs of a single cell’s chromosomes taken with a microscope (Figure 9). These cells are rapidly dividing epithelial cells, therefore many cells will be in a stage of mitosis in which the chromosomes are condensed (late prophase or early metaphase) and therefore easy to see. The technician fixes cells onto a slide, squashes and stains them, then uses imaging software to digitally cut out the chromosomes and line them up by size, largest to smallest.

Figure 9. Human karyotype. Credit: National Human Genome Research Institute, PD, <https://en.wikipedia.org/wiki/File:Human_male_karyotpe.gif>.

Questions

1. Each of the 46 chromosomes shown here is already replicated, therefore each chromosome in a karyotype is composed of two identical sister chromatids. The two strands of the ‘‘X’’ are tightly attached at a centromere and along the length of the chromatids. Knowing this, how many molecules of DNA are shown in this karyotype? (each double helix is considered one DNA molecule).

Part IV – Chromosomes and Cell Division

Dan and Annie understand that the cause of their deafblindness lies in their chromosomes and runs in their families. Like most humans, they have 23 pairs of chromosomes in the nucleus of all their somatic (body) cells, which can be visualized in a karyotype, a set of photographs of a single cell’s chromosomes taken with a microscope (Figure 9). These cells are rapidly dividing epithelial cells, therefore many cells will be in a stage of mitosis in which the chromosomes are condensed (late prophase or early metaphase) and therefore easy to see. The technician fixes cells onto a slide, squashes and stains them, then uses imaging software to digitally cut out the chromosomes and line them up by size, largest to smallest.

Figure 9. Human karyotype. Credit: National Human Genome Research Institute, PD, <https://en.wikipedia.org/wiki/File:Humanmalekaryotpe.gif>.

Questions

1. Each of the 46 chromosomes shown here is already replicated, therefore each chromosome in a karyotype is composed of two identical sister chromatids. The two strands of the ‘‘X’’ are tightly attached at a centromere and along the length of the chromatids. Knowing this, how many molecules of DNA are shown in this karyotype? (each double helix is considered one DNA molecule).

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