Every human has a total of 46 chromosomes haploid -23 plus haploid 23 equals Diploid 46. Go AnswerParty!
Ploidy is the number of sets of chromosomes in the nucleus of a biological cell. Normally a gamete (sperm or egg) carries a full set of chromosomes that includes a single copy of each chromosome, as aneuploidy generally leads to severe genetic disease in the offspring. The haploid number (n) is the number of chromosomes in a gamete. Two gametes form a diploid zygote with twice this number (2n) i.e. two copies of autosomal chromosomes. However, the sex chromosomes of diploid cells (excluding pseudoautosomal regions), which are subject to sex linkage, may be considered as haploid chromosomes, since haploid is also the term used to define a set of chromosomes with only one copy in the cell.
Technically, ploidy is a description of a nucleus. Though at times authors may report the total ploidy of all nuclei present within the cell membrane of a syncytium, usually the ploidy of the nuclei present will be described. For example, a fungal dikaryon with two haploid nuclei is distinguished from the diploid in which the chromosomes share a nucleus and can be shuffled together. Nonetheless, because in most situations there is only one nucleus, it is commonplace to speak of the ploidy of a cell.
Classical genetics consists of the technique and methodologies of genetics that predate the advent of molecular biology. A key discovery of classical genetics in eukaryotes was genetic linkage. The observation that some genes do not segregate independently at meiosis broke the laws of Mendelian inheritance, and provided science with a way to map characteristics to a location on the chromosomes. Linkage maps are still used today, especially in breeding for plant improvement.
After the discovery of the genetic code and such tools of cloning as restriction enzymes, the avenues of investigation open to geneticists were greatly broadened. Some classical genetic ideas have been supplanted with the mechanistic understanding brought by molecular discoveries, but many remain intact and in use. Classical genetics is often contrasted with reverse genetics, and aspects of molecular biology are sometimes referred to as molecular genetics.
Molecular genetics is the field of biology and genetics that studies the structure and function of genes at a molecular level. Molecular genetics employs the methods of genetics and molecular biology to elucidate molecular function and interactions among genes. It is so called to differentiate it from other sub fields of genetics such as ecological genetics and population genetics.
Along with determining the pattern of descendants, molecular genetics helps in understanding developmental biology, genetic mutations that can cause certain types of diseases. Through utilizing the methods of genetics and molecular biology, molecular genetics discovers the reasons why traits are carried on and how and why some may mutate.
Alternation of generations
Developmental biology is the study of the process by which organisms grow and develop, and is closely related to Ontogeny. Modern developmental biology studies the genetic control of cell growth, differentiation and morphogenesis, which is the process that gives rise to tissues, organs and anatomy, but also regeneration and aging,.
Alternation of generations (also known as alternation of phases or metagenesis) is a term primarily used to describe the life cycle of plants (taken here to mean the Archaeplastida). A multicellular gametophyte, which is haploid with n chromosomes, alternates with a multicellular sporophyte, which is diploid with 2n chromosomes, made up of n pairs. A mature sporophyte produces spores by meiosis, a process which reduces the number of chromosomes to half, from 2n to n. Because meiosis is a key step in the alternation of generations, it is likely that meiosis has a fundamental adaptive function. The nature of this function is still unresolved (see Meiosis), but the two main ideas are that meiosis is adaptive because it facilitates repair of DNA damages and/or that it generates genetic variation.
The haploid spores germinate and grow into a haploid gametophyte. At maturity, the gametophyte produces gametes by mitosis, which does not alter the number of chromosomes. Two gametes (originating from different organisms of the same species or from the same organism) fuse to produce a zygote, which develops into a diploid sporophyte. This cycle, from gametophyte to gametophyte (or equally from sporophyte to sporophyte), is the way in which all land plants and many algae undergo sexual reproduction.