Water 3. Protein 5. Enzymes 6. Cell Respiration 9. Photosynthesis 3: Genetics 1. Genes 2. Chromosomes 3. Meiosis 4. Inheritance 5. Genetic Modification 4: Ecology 1. Energy Flow 3. Carbon Cycling 4. An allele determines a specific trait of a particular organism. These traits pass from one generation to the other by sexual reproduction. The process of allele transmission was first described by the law of segregation by Gregor Mendel in The diploid organisms present two alleles of the same gene since they contain two sets of chromosomes.
This allele pair can contain either the same nucleotide sequence homozygous or different nucleotide sequences heterozygous. In the heterozygous condition, only one allele is expressed, and the other is in the repressed form.
The expressing allele is called the dominant allele, and the repressed allele is called the recessive allele. The complete masking of the recessive allele by the dominant allele is called the complete dominance. Complete dominance is a type of Mendelian inheritance. Figure 1: Different Eye Colors. The non-Mendelian inheritance patterns include incomplete dominance , codominance , multiple alleles , and polygenic traits. In incomplete dominance, both alleles in the heterozygous pair are expressed.
In codominance, a mixed phenotype of both alleles in the heterozygous allele pair can be observed. Multiple alleles are the presence of more than two alleles in the population to determine a particular trait. In polygenic traits, the phenotype is determined by many genes. Skin color, eye color, height, weight, and hair color of humans are polygenic traits.
If a female has a disorder in which she has more than two X chromosomes, the extra chromosomes tend to be inactive. Thus, having one or more extra X chromosomes causes far fewer developmental abnormalities than having one or more extra nonsex chromosomes. Genes contain Males who have more than one Y chromosome Home. There are several types of chromosome abnormalities Overview of Chromosome and Gene Disorders Chromosomes are structures within cells that contain a person's genes.
A gene is a segment of deoxyribonucleic acid DNA and contains the code for a specific protein that functions in one or A person may have an abnormal number of chromosomes or have abnormal areas on one or more chromosomes. Many such abnormalities can be diagnosed before birth see Testing for chromosome and gene abnormalities Testing for chromosome and gene abnormalities Chromosomes are structures within cells that contain a person's genes.
Abnormal numbers of nonsex chromosomes usually result in severe abnormalities. For example, receiving an extra nonsex chromosome may be fatal to a fetus or lead to abnormalities such as Down syndrome Down Syndrome Trisomy 21 Down syndrome is a chromosome disorder caused by an extra chromosome 21 that results in intellectual disability and physical abnormalities. Down syndrome is caused by an extra chromosome Absence of a nonsex chromosome is fatal to the fetus. Large areas on a chromosome may be abnormal, usually because a whole section was left out called a deletion or mistakenly placed in another chromosome called translocation.
For example, chronic myelogenous leukemia Chronic Myeloid Leukemia CML Chronic myeloid leukemia is a slowly progressing disease in which cells that normally would develop into neutrophils, basophils, eosinophils, and monocytes become cancerous see also Overview This abnormality can be inherited or be the result of a new mutation Mutation Genes are segments of deoxyribonucleic acid DNA that contain the code for a specific protein that functions in one or more types of cells in the body.
Mitochondria Cells Often thought of as the smallest unit of a living organism, a cell is made up of many even smaller parts, each with its own function.
Unlike other structures inside cells, each mitochondrion contains its own circular chromosome. This chromosome contains DNA mitochondrial DNA that codes for some, but not all, of the proteins that make up that mitochondrion.
Mitochondria from the sperm usually do not become part of the developing embryo. A trait is any gene-determined characteristic. Many traits are determined by the function of more than one gene. For example, a person's height is likely to be determined by many genes, including those affecting growth, appetite, muscle mass, and activity level.
However, some traits are determined by the function of a single gene. Variation in some traits, such as eye color or blood type, is considered normal. Other variations, such as albinism Albinism Albinism is a rare hereditary disorder in which little or none of the skin pigment melanin is formed. The skin, hair, and eyes, or sometimes just the eyes, are affected. Typically, the hair This syndrome is caused However, not all such gene abnormalities are uniformly harmful.
For example, one copy of the sickle cell gene can provide protection against malaria, but two copies of the gene cause sickle cell anemia. A genetic disorder is a detrimental trait caused by an abnormal gene. The abnormal gene may be inherited or may arise spontaneously as a result of a new mutation.
Gene abnormalities are fairly common. Every humans carries an average of to abnormal genes different ones in different people. However, most of the time the corresponding gene on the other chromosome in the pair is normal and prevents any harmful effects.
In the general population, the chance of a person having two copies of the same abnormal gene and hence a disorder is very small. However, in children who are offspring of close blood relatives, the chances are higher.
Chances are also higher among children of parents who have married within an isolated population, such as the Amish or Mennonites. Merck and Co. From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world. The Manual was first published in as a service to the community. Learn more about our commitment to Global Medical Knowledge.
This site complies with the HONcode standard for trustworthy health information: verify here. Common Health Topics. Pairing Sex chromosomes Chromosome abnormalities Mitochondrial chromosomes. Genetic Disorders. Also, loci are important in gene mapping and constructing a genetic map of an organism. Based on their functions, the difference between allele and locus is that the allele codes for a trait while the locus gives residence to a gene. Allele and locus differ with each other even though alleles locate at loci.
Therefore, the allele is one possible form of a gene. On the other hand, the locus is a specific location on a chromosome where a gene situates. Loci are genetic markers. There can be more than a single allele in one locus. Furthermore, allele codes for a gene, while locus is just a position on the chromosome. This is the difference between allele and locus. Available here 2. Available here. Samanthi Udayangani holds a B.
Degree in Plant Science, M.
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