Where is chromosome

Each chromosome is made of protein and a single molecule of deoxyribonucleic acid DNA. Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique. The term chromosome comes from the Greek words for color chroma and body soma. Scientists gave this name to chromosomes because they are cell structures, or bodies, that are strongly stained by some colorful dyes used in research.

The unique structure of chromosomes keeps DNA tightly wrapped around spool-like proteins, called histones. Without such packaging, DNA molecules would be too long to fit inside cells. For example, if all of the DNA molecules in a single human cell were unwound from their histones and placed end-to-end, they would stretch 6 feet.

For an organism to grow and function properly, cells must constantly divide to produce new cells to replace old, worn-out cells. During cell division, it is essential that DNA remains intact and evenly distributed among cells. Chromosomes are a key part of the process that ensures DNA is accurately copied and distributed in the vast majority of cell divisions.

Still, mistakes do occur on rare occasions. Changes in the number or structure of chromosomes in new cells may lead to serious problems. For example, in humans, one type of leukemia and some other cancers are caused by defective chromosomes made up of joined pieces of broken chromosomes.

It is also crucial that reproductive cells, such as eggs and sperm, contain the right number of chromosomes and that those chromosomes have the correct structure. If not, the resulting offspring may fail to develop properly. For example, people with Down syndrome have three copies of chromosome 21, instead of the two copies found in other people. Chromosomes vary in number and shape among living things. Most bacteria have one or two circular chromosomes. However, in meiosis, the parent cell produces four haploid daughter cells each containing half of the parent cells chromosomes, or 23 chromosomes.

The critical difference between mitosis and meiosis is that mitosis produces two genetically identical daughter cells, whereas meiosis produces four genetically different daughter cells. The phases of cell division are similar for both mitosis and meiosis, and both processes result in cytokinesis cytoplasmic division of the daughter cells.

However, in meiosis, the cycle occurs twice meiosis I and meiosis II before the four haploid daughter cells are produced. Another difference between the stages of mitosis and meiosis is that in meiosis, homologous chromosomes pair up during metaphase instead of chromatids.

In a homologous pair, one chromosome comes from the mother, and one chromosome comes from the father. Homologous chromosomes are very similar, but they are not identical.

They carry the same genes eg, hair or eye color , but they may not code for the same trait eg, blonde hair or brown eyes. Occurs before cell division. Consists of three stages: Gap 1 growth , S phase DNA replication and Gap 2 continues growth, prepares for cell division. Tell us what you think about Healio. What is a Genome? Whole-Exome Sequencing vs. Visit Healio. Open survey. In: Facts In the Cell. Related Content:. What is a cell? What is DNA? What is a telomere?

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