What’s the Difference Between a Gene and an Allele? | promovare-site.info
As per Pearson Campbell Biology "A gene is a region of DNA that can be expressed to . Historically the problem was the relation between trait and gene. Genes and alleles are genetic sequences, and both determine biological traits. So, what makes them different?. Humans have long observed that traits tend to be similar in families. It wasn't until the mid-nineteenth century that larger implications of genetic.
This means that the inheritance of an allele for yellow or green pea color is unrelated to the inheritance of alleles for white or purple flowers. This phenomenon, known as " Mendel's second law " or the "law of independent assortment," means that the alleles of different genes get shuffled between parents to form offspring with many different combinations.
Some genes do not assort independently, demonstrating genetic linkagea topic discussed later in this article. Often different genes can interact in a way that influences the same trait. In the Blue-eyed Mary Omphalodes vernafor example, there exists a gene with alleles that determine the color of flowers: Another gene, however, controls whether the flowers have color at all or are white. When a plant has two copies of this white allele, its flowers are white—regardless of whether the first gene has blue or magenta alleles.
This interaction between genes is called epistasiswith the second gene epistatic to the first. These complex traits are products of many genes. The degree to which an organism's genes contribute to a complex trait is called heritability. For example, human height is a trait with complex causes.
Bases pair through the arrangement of hydrogen bonding between the strands. The molecular basis for genes is deoxyribonucleic acid DNA. DNA is composed of a chain of nucleotidesof which there are four types: Genetic information exists in the sequence of these nucleotides, and genes exist as stretches of sequence along the DNA chain.
DNA normally exists as a double-stranded molecule, coiled into the shape of a double helix. Each nucleotide in DNA preferentially pairs with its partner nucleotide on the opposite strand: A pairs with T, and C pairs with G.
Thus, in its two-stranded form, each strand effectively contains all necessary information, redundant with its partner strand. This structure of DNA is the physical basis for inheritance: DNA replication duplicates the genetic information by splitting the strands and using each strand as a template for synthesis of a new partner strand.
In bacteriaeach cell usually contains a single circular genophorewhile eukaryotic organisms such as plants and animals have their DNA arranged in multiple linear chromosomes. These DNA strands are often extremely long; the largest human chromosome, for example, is about million base pairs in length. While haploid organisms have only one copy of each chromosome, most animals and many plants are diploidcontaining two of each chromosome and thus two copies of every gene.
Walther Flemming 's diagram of eukaryotic cell division. Chromosomes are copied, condensed, and organized. Then, as the cell divides, chromosome copies separate into the daughter cells. Many species have so-called sex chromosomes that determine the gender of each organism.
In evolution, this chromosome has lost most of its content and also most of its genes, while the X chromosome is similar to the other chromosomes and contains many genes.
Genetics - Wikipedia
The X and Y chromosomes form a strongly heterogeneous pair. Asexual reproduction and Sexual reproduction When cells divide, their full genome is copied and each daughter cell inherits one copy. This process, called mitosisis the simplest form of reproduction and is the basis for asexual reproduction. Asexual reproduction can also occur in multicellular organisms, producing offspring that inherit their genome from a single parent.
Offspring that are genetically identical to their parents are called clones. Eukaryotic organisms often use sexual reproduction to generate offspring that contain a mixture of genetic material inherited from two different parents. The process of sexual reproduction alternates between forms that contain single copies of the genome haploid and double copies diploid.
Diploid organisms form haploids by dividing, without replicating their DNA, to create daughter cells that randomly inherit one of each pair of chromosomes. Most animals and many plants are diploid for most of their lifespan, with the haploid form reduced to single cell gametes such as sperm or eggs. Some bacteria can undergo conjugationtransferring a small circular piece of DNA to another bacterium. Recombination and genetic linkage[ edit ] Main articles: Chromosomal crossover and Genetic linkage Thomas Hunt Morgan 's illustration of a double crossover between chromosomes.
The diploid nature of chromosomes allows for genes on different chromosomes to assort independently or be separated from their homologous pair during sexual reproduction wherein haploid gametes are formed.
Genes, Traits, and Proteins
In this way new combinations of genes can occur in the offspring of a mating pair. Genes on the same chromosome would theoretically never recombine.
Regulatory regions of the gene also contribute to protein synthesis by determining when the gene will be switched on or off. Sciencing Video Vault Proteins In active genes, genetic information determines which proteins are synthesized and when synthesis is turned on or off. These proteins fold into complicated three-dimensional structures, somewhat like molecular origami.
Because each amino acid has specific chemical characteristics, the sequence of amino acids determine the structure and shape of a protein. For example, some amino acids attract water, and others are repelled by it.
What’s the Difference Between a Gene and an Allele?
Some amino acids can form weak bonds to each other, but others cannot. Proteins that catalyze accelerate chemical reactions, for example, have "pockets," which can bind specific chemicals and make it easier for a particular reaction to occur. Variations in the DNA code of a gene can change either the structure of a protein or when and where it is produced.Heredity: Crash Course Biology #9
If these variations change the protein structure, they could also change its function. For example, a single, specific mutation in hemoglobin -- the oxygen-carrying protein abundant in your red blood cells -- affects oxygen transport and is enough to cause sickle-cell anemia.