A chromosome is a deoxyribonucleic acid DNA molecule with part or all of the genetic material genome of an organism. Most eukaryotic chromosomes include packaging proteins which, aided by chaperone proteins , bind to and condense the DNA molecule to prevent it from becoming an unmanageable tangle. Chromosomes are normally visible under a light microscope only when the cell is undergoing the metaphase of cell division where all chromosomes are aligned in the center of the cell in their condensed form. The original chromosome and the copy are now called sister chromatids. During metaphase the X-shape structure is called a metaphase chromosome. In this highly condensed form chromosomes are easiest to distinguish and study.
Sex chromosomes are particular chromosomes that are involved in determining the sex of an organism. In the cells of humans and many other organisms the sex chromosomes consist of a pair of chromosomes called the X and Y chromosomes. The X and Y chromosomes were first discovered in beetles by Nettie Stevens in She noticed that cells of female beetles had identical looking pairs of each of their several chromosomes, but that male beetles had one pair in which the chromosomes were very different in appearance from each other. She called these two chromosomes the X and the Y, and found that female beetles differed from males in containing two X chromosomes. The same situation is also found in humans where females are XX and males are XY. The X and Y chromosomes in humans are also very different in appearance, with the X chromosome being considerably larger than the Y.
Sex Determination: 3 Basic Types of Sex Determination Processes
Skip navigation. The Y-chromosome is one of a pair of chromosomes that determine the genetic sex of individuals in mammals, some insects , and some plants. In the nineteenth and twentieth centuries, the development of new microscopic and molecular techniques, including DNA sequencing, enabled scientists to confirm the hypothesis that chromosomes determine the sex of developing organisms. In an adult organism, the genes on the Y-chromosome help produce the male gamete, the sperm cell. Beginning in the s, many studies of human populations used the Y-chromosome gene sequences to trace paternal lineages.
Read this article to learn about the important types of sex determination by in inheritance:. Image Courtesy : microbix. They occur in somatic cells of animals and vascular plants which possess diploid number of chromosomes. Out of the two homologous chromosomes present in an individual, one is derived from the father parent and the other from the mother parent. The two homologous chromosomes of each type do not occur attached to each other in the nucleus of the cell.