Human genetic disorders can arise as a consequence of mutations in Essay

Human genetic disorders can arise as a consequence of mutations in either nuclear or mitochondrial genomes. Using specific examp - Essay Example These are called so because they carry genes for the determination of the sex of the newborn and they are also of two types i.e. X & Y chromosomes where X is for female and Y for Male. The chromosomes are mainly classified either on the basis of their banding or on the basis of the position of the centromere i.e. the central point of every chromosome. The basic constitutive component of these DNA molecules, euchromatin and heterochromatin is the main factor on which the DNA on all these chromosomes differ from each other. Still, on some of the chromosomes e.g. 1, 9 and 16 show heterochromatin in their centromere region where as Chromosome Y is also considered to contain more heterochromatin. (T. STRACHAN and A. READ, 2004,p19) Mitochondrial genes There usually are two strands in mitochondrial genome i.e. H and L strand. The H strand is supposed to encode more genes i.e. 28 out of 37 where as the L strand encodes the remaining number of genes. The mitochondrial genome is not very much similar to the nuclear genome as it does not contain any introns as well as it is very much compact and tightly packed as compared to the loosely packed nuclear genome. Most of the coding sequences are separated by one or two of the non coding bases while overlapping is observed in only some of the coding sequences. In some genes post transcription introduction of of UAA codon i.e. termination codon is necessary since they lack their own termination codons. (T. STRACHAN and A. READ, 2004,p19) Figure 9.3 The organization of the human mitochondrial genome. The H strand is transcribed from two closely spaced promoter regions fl anking the tRNAPhe gene (grouped here as PH); the L strand is transcribed from the PL promoter in the opposite direction. In both cases, large primary transcripts are produced and cleaved to generate RNAs for individual genes. All genes lack introns and are closely clustered. The symbols for protein-coding genes are shown here without the prefi x MT- that signi fi es mitochondrial gene. The genes that encode subunits 6 and 8 of the ATP synthase (ATP6 and ATP8) are partly overlapping. Other polypeptide-encoding genes specify seven NADH dehydrogenase subunits (ND4L and ND1–ND6), three cytochrome c oxidase subunits (CO1–CO3), and cytochrome b (CYB). tRNA genes are represented with the name of the amino acid that they bind. The short 7S DNA strand is produced by repeat synthesis of a short segment of the H strand (see Figure 9.2). COMPARISON OF NUCLEAR AND MITOCHONDRIAL GENOME (T. STRACHAN and A. READ, 2004,p21) Single gene disorders These mainly include autosomal, X linked and Y linked. These disorders are called as Mendelian disorders as they follow the mendelian order of inheritance. Some other disorders such as Non mendelians ones are also included in the list. (AKUL MEHTA.2012) Both the sperm and the egg contribute to the formation nuclear genome in the zygote whereas the mitochondrial is supposed to take the sequence from t he egg only.(T. STRACHAN and A. READ, 2004) Autosomal dominant These disorders are usually common in the offsprings who have one of the two parents with the abnormality. These disorders are mainly caused by mutation in one of the genes only with the 50 % possibility of getting the mutated gene. The disease usually develops later in the life or it would even not appear at all as the penetrance