Chromosomes, genes, alleles, mutations Topic 4.1 Chromosomes, genes, alleles, mutations

4.1.1 State that eukaryotic chromosomes are made of DNA and proteins In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure. Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing. However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope. Most of what researchers know about chromosomes was learned by observing chromosomes during cell division.

4.1.2 Define gene A gene is a segment of DNA, located on the chromosomes, that carries hereditary instructions from parent to offspring. A gene codes for a protein that gives a characteristic.

4.1.2 Define allele For each gene, an organism typically receives one allele from each parent. An allele is one specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene.

4.1.2 Define genome Genome is the whole of the genetic information of an organism.

4.1.3 Define gene mutation A gene mutation is a permanent change in the DNA sequence that makes up a gene . may produce a different amino acid sequence in the protein translated. may not change the protein because of the degenerate nature of the genetic code. expression of the mutated gene may or may not be beneficial to the organism. Substances that cause mutation are called mutagens and include chemicals and radiation. 

4.1.4 Sickle-cell anemia mutation Effect on the phenotype animation