Survey of Human Genetics - Research Paper Example

Survey of Genetics: Phenotypes, Pedigree Analysis, and Allelic Expression Phenotypes are the appearances, physical traits, and even the behavioral patterns that any particular organism possesses. This is distinct from the genotype which specifically refers to the genetic materials that a life form inherits from its parents (Genotype/Phenotype Distinction, 2004). Organisms that reproduce sexually, by the fusion of two haploid cells to produce a new diploid zygote, hold two copies of any particular gene.

Except for the sex chromosomes in males, all such organisms receive a duplicate set of genetic materials. Animals and most plants are endowed with two copies of each gene, one copy from each of its progenitors. For numerous reasons the two copies of the same gene are not always exactly identical. There are often times two or more alternative forms for any particular gene. Genes that code for analogous proteins but have slightly different nucleotide sequences are called alleles (Alleles, 2009).

An organism may possess only two alleles for any particular gene, and these alleles may be the same or different. All the variations within the genomes of each species are expressed through the various combinations of alleles, and this gives rise to the patterns of allelic expression. The different possible combinations of alleles directly result in some of the variation in physical characteristics which we observe in different members of the same species. These ideas about genes and their influence on physical traits come from the work of Gregor Mendel who is known as the "father of genetics".

Mendel was a priest and scientist who lived in Austria during the 1800's, he performed experiments with peas. He observed that one group of pea plants produced peas that were always yellow and smooth. Another set of pea plants only produced peas that were green and wrinkled. When Mendel mated the two groups of plants, he found that all of the offspring produced peas that were yellow and smooth. The physical characteristics of yellow color and smooth texture totally covered over any tendency towards green or wrinkly peas.

Mendel concluded that the yellow/smooth phenotype was dominant to the green/wrinkled phenotype. A second experiment in which he mated two members of this second generation of peas produced an interesting result. Some of the offspring produced yellow/smooth peas and some produced green/wrinkly peas. The recessive trait of green/wrinkly peas expressed itself in the next generation!Pedigree analysis is a means to predict the possibility that a particular phenotype will appear in a new offspring based on the physical characteristics of its predecessors.

In animals this could help to predict the likelihood of skin, hair, and eye color. Perhaps more importantly, pedigree analysis can be used to detect the likelihood that any particular disease with a strong genetic tendency will be passed from parent to offspring. Many people are interested in discovering what their child might be like, based on information about the health of parents and grandparents. Illnesses such as cystic fibrosis, Tay-Sachs disease, sickle cell anemia, and maple syrup urine disease are known to be genetically inherited (Genetic Conditions, 2009).

All of these conditions are specifically autosomal recessive. This means that it is possible that neither the parents nor the grandparents of the individual had the disease. In this sense, pedigree analysis that takes into account only the phenotypes can be very limiting. However, if one grandparent from the mother and one grandparent from the father had any of these diseases then the child will most definitely inherit the disease. Modern medical genetic counseling analyzes not just the phenotypes of all known relatives but also the genotypes of both parents.

Only by directly observing the nucleotide sequences of the parent's genes, it is possible to determine the presence of a recessive allele.ReferencesGenotype/Phenotype Distinction (2004).stanford.edu. Referenced 20 April 2009 Alleles (2009).thefreedictionary.com. Referenced 20 April 2009 Genetic Conditions (2009).nih.gov. Referenced 20 April 2009