Genes are segments of DNA that controls the proteins production and the cell cycle. Linked genes are genes that are inherited together; linked genes have genes for the same traits arranged in the same order. There are a total of three different types of linkage groups: 1. Non-linkage: Independent assortment of alleles. Genes on different chromosomes. 2. Complete linkage: Genes on a chromosome inherited as a unit. 3. Partial linkage: Intermediate behavior between non-linkage and linkage. From partial linkage analysis we can learn about the order and spacing of genes on chromosomes. .
In prophase 1 chromosomes coil up and a spindle forms. Then in a step unique to meiosis, each pair of linked genes come together, matched gene by gene, to form a four-part structure called a tetrad. A tetrad consists of two homologous chromosomes, each made up of two sister chromatids .The chromatids in a tetrad pair so tightly that nonsiter chromatids from the linked genes sometimes actually exchange genetic material in a process know as crossing over. Genetic variation is very important for organisms, genetic recombination is the cause of the variation which is a reassortment or crossing over during meiosis. Genes do not exist free in the nucleus cell; they are lined up on chromosomes. Also linked genes are paired on the same chromosome.
Chromosomes are cell structures that carry the genetic material that is copied and passed from generation to generation of cells. In humans the 23rd pair of chromosomes is the sex chromosomes, which determine the sex of an individual and carry sex-linked characteristics. Genes located on the sex chromosomes are called sex-linked genes; usually refers to X-linked genes. The female carries XX sex chromosomes, and the male carries XY chromosomes. Also, pairs of matching homologous chromosomes in somatic cells are called autosomes.
Any change or random error in a DNA sequence is a mutation.