Explain the reason and types of inborn error of metabolism in human.

Inborn errors of metabolism (IEM) are genetic conditions that affect the metabolic pathways involved in the breakdown of nutrients and the generation of energy. The common inborn metabolic disorders are: 1. Hereditary fructose intolerance (HFI) is a metabolic disease caused by the absence of an enzyme called aldolase B. In people with HFI, ingestion of fructose and sucrose causes severe hypoglycaemia and the build up of dangerous substances in the liver. 2. Galactosemia-Galactosemia is a rare, hereditary disorder of carbohydrate metabolism that affects the body's ability to convert galactose to glucose. 3.Maple syrup urine disease (MSUD) is a rare but serious inherited condition. It means the body cannot process certain amino acids, causing a harmful build-up of substances in the blood and urine. Normally, our bodies break down protein foods such as meat and fish into amino acids. 4.Phenylketonuria (PKU) Phenylketonuria, also called PKU, is a rarely inherited disorder that causes an amino acid called phenylalanine to build up in the body. PKU is caused by a defect in the gene that helps create the enzyme needed to break down phenylalanine.

Explain the Genetic balance theory of Drosophila with chart.

The theory of genic balance was given by Calvin Bridges in 1926 who studied it in the Drosophila melanogaster . He stated that instead of XY chromosomes, sex is determined by the genic balance or ratio between X-chromosomes and autosome genomes. He found that genic ratio X/A of 1 produces fertile females whether the flies have XX+2A or XXX+3A chromosomes. A genic ratio of 0.5 produces male fruit fly. This takes place in XY+2A as well as X0+2A which means that the expression of maleness is not controlled by Y-chromosomes but instead gets localised on autosomes. The X-chromosomes will carry female determining genes. Bridges further proposed that genetic ratio of less than 0.5 will produce meta-males. On the other hand, genic ratio between 0.5 to 1.0 will produce intersexes with a lot of sexual abnormalities and morphological abnormalities. Super females or sterile meta-females are produced with a genic ratio of 1.5. the super females and meta-females have been called girls of fly and glamour boys by Dodson

"Complete linkage is rare" explain it with a suitable example.

Complete linkage is the tendency of genes present in the same chromosome to remain in their original combination and enter together without crossover into the same gamete. In 1910, Morgan announced "Chromosome Theory of Linkage" while working on Drosophila, claiming that coupling and repulsion are two aspects of the association. He defined complete linkage as the tendency of genes present in the same chromosome to remain in their original combination and enter together without crossover into the same gamete. Genes are closely linked in this form of association, and appear to stay together. During meiosis, the attachment is broken down by the act of crossing over. If genes are so closely connected that they are still expressed together, they are not crossed over, the relation between them is called complete as illustrated in an example below: Where a male Drosophila and female silkworm ( Bombyx mori ) have 100% parental combinations showed that the body colour gene is entirely correlated with long wings. The phenotypic F2 ratio in this dihybrid is 3:1, and the test cross-ratio is 1:1 (like a monohybrid). In the case of male Drosophila recombinant forms are absent due to lack of crossing over. This means that in their original configuration all the genes that originate on a single chromosome will end up on the same chromosome. Only parental phenotypes are predicted, in the absence of recombination.

Discuss the role of chromosomes other than the sex-chromosome in the determination of sex.

An allosome is a sex chromosome. Allosomes help in determining the sex of an individual by the virtue of the Y chromosomes. An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome pairs which may have different structures. Autosomes still contain sexual determination genes even though they are not sex chromosomes. For example, the SRY gene on the Y chromosome encodes the transcription factor TDF and is vital for male sex determination during development. TDF functions by activating the SOX9 gene on chromosome 17, so mutations of the SOX9 gene can cause humans with an ordinary Y chromosome to develop as females.

Write the chromosomal disorder in Down's syndrome and write any three symptoms of it.

Down's syndrome is a chromosomal abnormality that where the 21st chromosome is affected. This condition is called trisomy 21 where the person has three copies of chromosome 21, instead of the usual two copies, in all cells. This is caused by abnormal cell division during the development of the sperm cell or the egg cell. The most common symptoms of Down's syndrome are: A flattened face, especially the bridge of the nose. Almond-shaped eyes that slant up. A tongue that tends to stick out of the mouth.