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3 Cards in this Set
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- Back
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Distinguish among chromatin, chromosomes, homologous chromosomes, & sister chromatids.
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Chromatin are long and thin (DNA replication occurs in chromatin form). Chromosomes are coiled and condensed structures made of DNA and proteins. They are the form of genetic material of a cell during cell division. Homologous chromosomes are chromosomes that code for the same genes but may have different alleles for these genes. In a homologous pair, one chromosome comes from the mother and the other from the father. Sister chromatids are two identical copies of a single chromosomes that are connected by a centromere. Sister chromatids contains the same genes (they code for the same proteins) where non sister chromatids do not.
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Compare gene & Allele
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A gene is a unit or segment of DNA which codes for a particular protein. An allele is a different version of a gene. Most genes come in several varieties so they have several or even many different alleles or forms in any given population. Different alleles of genes are caused by mutations - the sequence of amino acids in the protein in question, are altered. Mutations which are not fatal produce the variations of genes which we know as alleles.
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Contrast phases of meiosis.
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There are four phases in Meiosis 1: Prophase 1, Metaphase 1, Telophase 1, and Anaphase 1. In Prophase 1, the nuclear envelope disappears, chromosomes condense, and the centrioles begin to migrate to opposite poles of the cell, with the spindle fibers growing between them. During this time, the homologous chromosomes form pairs and the cell starts as diploid. In metaphase 1, the 23 Pairs of homologous chromosomes line up along the equator of the cell. The spindles then connect to the kinetochores (proteins on the centromere). In Anaphase I, the spindle fibers shorten, and the homologous chromosome pairs are separated from each other. One chromosome from each pair moves toward one pole, with the other moving toward the other pole, resulting in a cell with 23 chromosomes at one pole and the other 23 at the other. The sister chromatids remain attached at the centromere. In Telophase I, the spindle fiber disassembles and the nucleus reforms.
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