The Meaning of Genotype and Phenotype and the Effect of the Environment on the Phenotype of an Organism - Coursework Example

The Meaning of Genotype and Phenotype and the Effect of the Environment on the Phenotype of an Organism The genotype of organism is its genetic makeup. The genes that cause appearance of specific characteristics in an organism are called its genotype. On the other hand, Phenotypes are organism’s observable characteristics. These characteristics can be the organism’s morphology, development, biochemical or physiological properties, and behavior. The phenotype is expressed as a result of expression of the genotype. Consider the human CFTR gene. The CFTR gene which for encodes a protein that transports chloride ions across cell membranes has two genes. The dominant gene (A), which is the normal version of the gene. The recessive gene (a), which is the mutated version of the gene. Those with cystic fibrosis receive both the recessive alleles. The genotype of individuals is then (a, a). While the phenotype of the recessive genotype, is the absence of protein that transports chloride ions, and so, cystic fibrosis. Phenotype is not only expressed by the affects of the phenotype alone. The environmental condition also affects the expression of phenotype. The effect of the environment on the phenotype of an organism is best understood through an experiment. Taking two samples of the colcus plant, both samples originate from the same plant. The samples are grown in two separate chambers. The environmental condition varied is the amount of light delivered. All other factors are kept constant in both samples. Though both samples have similar genotypes, the growth of both samples varies. The sample that receives higher proportion of light compared to the other grows faster and thrives. While the sample that receives lesser light compared to the other, has stunted growth and is weak. The environmental condition has affected the phenotype irrespective of the genotype being common to both samples. Explain how DNA replicates itself. (200 words) DNA replication is based on the model presented by Watson and Crick. The model suggests semi conservative replication of DNA strands. This replication is called so, because a half of the strand is conserved while the other half is newly formed. DNA replication occurs in the nucleolus of the nucleous.DNA replication takes place in the interphase of the cell cycle. In order for DNA replication to take place, the DNA strands must first be separated. The DNA strands are separated by the enzymatic action of an enzyme. The enzyme breaks the hydrogen bonds present between the complementary base pairs. The two DNA strands are separated. The four bases involved in DNA replication are adenine, thymine, cytosine and guanine. Nucleotides when paired with an additional phosphate become activated nucleotides. The activated nucleotides are capable of pairing up with their complementary base pairs with the help of enzyme DNA polymerase. The activated nucleotides form bonds with their complimentary base pairs. DNA polymerase links the sugar and innermost phosphate groups of adjacent nucleotides together. The extra phosphate ions are released. This marks the replication of DNA from a single DNA molecule; both new DNA molecules conserve a single strand of the old DNA molecule. Explain the type of mutation that resulted in the sickle cell anaemia. (200 words) Mutation is the change in genetic material of an organism as results of base deletion, base substitution or base addition. The change in genetic material causes a different allele of a gene to be expressed, which in turn causes different phenotypic characteristic. Sickle cell anaemia is an inherited blood disorder that causes a change in haemoglobin characteristic. Haemoglobin is composed of four polypeptide chains. That is two alpha chains and two beta chains. The normal coding for haemoglobin in the beta chains is; Val-His-Leu-Thr-Pro-Glu-Glu-Lys-. These coding codes for normal haemogobin. However, a base substitution, causes the normal base sequence CTT to be expressed as CAT. This base substitution causes the coding to be as; Val-His-Leu-Thr-Pro-Val-Glu-Lys-. That is the expression of amino acid Valine instead of Glutamic acid. The difference in coding has little difference when haemoglobin molecules are attached with oxygen. However, when haemoglobin is not combined with oxygen, deoxygenated blood, the mutated beta chains make haemoglobin less soluble. The haemoglobin molecules form long fibers inside the red blood cells, which causes the red blood cells to be shaped like a half moon or sickle. The distorted shape of the red blood cells decreases their efficiency to bind with oxygen, and to transport it. Explain the processes of transcription and translation during protein synthesis (300 words) Transcription refers to the process of creation of messenger RNA (mRNA) from DNA molecules. The process occurs in the nucleus. A portion of the DNA molecule that is to be expressed is unwound. Free activated RNA nucleotides pair up through complementary base pairing with the exposed DNA strand. The activated RNA nucleotides have their sugar-phosphate groups bonded together to form sugar phosphate backbone. The RNA molecule that is formed is called mRNA. The mRNA leaves the nucleus into the cytoplasm through the nuclear pore in the nuclear envelope. Translation refers to the formation of a polypeptide chain with help from the mRNA chain and transfer RNA (tRNA). In the cytoplasm there exists free amino acid molecules and tRNA’s. The structure of tRNA consists of an end that bond with the free amino acid, and an end that has a base triplet. The base triplet is known as the anticodon. The anticodon has complementary base pairs with the base triplets present on the mRNA. Each tRNA has a specific anticodon sequence and is capable of binding with a specific amino acid. The mRNA the entered the cytoplasm attaches itself to a ribosome. Ribosome’s are known as protein factories, which explain their function. The ribosome consists of ribosomal RNA (rRNA) and protein. They consist of a small and large subunit. The mRNA binds with the small subunit, while tRNA binds with the large subunit. The mRNA strand exposes 6 bases at a time to the large subunit. The mRNA exposes its triplet base pairs to tRNA that binds with the large subunit of rRNA. If a complementary base pair is formed between mRNA and tRNA then hydrogen bonds form between the two triplet bases. A second tRNA matches with the next triplet base exposed to the large subunit of rRNA. The second tRNA forms complementary base pairs with the mRNA strand, a peptide bond forms between the two amino acids with the help of enzyme peptidyl transferase. Both tRNA molecules then detach and the ribosome reads the next 6 bases on the mRNA. The polypeptide chain continues to form until a stop codon is reached; UAA, UAG, UGA. Bibliography Read More