Question LR 1 (8 pts) Genetics is the study of the role of genes in heredity. Ex

Question

Question LR 1 (8 pts) Genetics is the study of the role of genes in heredity. Explain how genes contribute to an organism's traits and how genes are inherited from cell to cell. You should use the following terms in your answer: DNA, protein, genotype, phenotype, gene expression, base pair, complementary, DNA synthesis, mitosis, double-stranded Question LR_2 (4 pts) Explain at the molecular level why many hereditary genetic diseases follow simple Mendelian inheritance patterns, whereas quantitative traits, such as blood pressure, display complex inheritance patterns.

Explanation / Answer

1. Cell is the unit of life. Every cell contains DNA and it stores the genetic information of cell/organism. DNA is made of nucleotide (which is formed by nitrogenous base, phosphate and deoxyribose sugar). It is a double helical structure in which both strands are antiparallel to each other and nitrogenous base project inside helix. Nitrogenous bases (adenine, guanine, cytosine and thymidine) pair with one another, ADENINE pairs with THYMIDINE, and GUANINE pairs with CYTOSINE (these are called complementary base pairs). A DNA strand can contain up to millions of bade pairs. It is this particular sequences of base pairs that makes a GENE and GENOME is set of all genes in organism. This genome make the GENOTYPE of an organism.

The central dogma of molecular biology states that DNA forms RNA by transcription and RNA forms PROTEIN by translation. When DNA is transcribed into RNA then Adenine pairs with URACIL and Guanine with cytosine. These bases in RNA are paired in group of 3 and are called CODONS. These codons code for specific amino acids (and protein is polymer of amino acid). The sequence of these codons on DNA determines the sequence of amino acid in protein. Proteins are workhorse of gene. They forms basic structure of cell. They form enzymes and these enzymes can be used for formation of other biomolecules like lipid, carbohydrates. Each enzyme has different protein which different in sequence of amino acid (which is determined by sequence of base in RNA which in turn is determined by sequence of base on DNA). The protein with other biomolecules form the organism's observable characteristics which is called PHENOTYPE.

The GENES are inherited from parent to daughter cell by cell division (mitosis and meiosis). DNA which is storehouse of gene is replicated during cell division and the daughter cell receives identical DNA copy from parent cell thus the daughter cell has same genes as the parent cell. This is inheritance of genes.

2. Hereditary genetic disorders are usually caused by defect in single gene. There are usually 2 variant of single gene called as alleles. These alleles are present in sister chromatids and when the cell divides these alleles separate independently of each other. Thus progeny usually receive one copy of allele from each parent. Thus if one parent has defect in gene then it would be inherited to progeny. This is in accordance with Mendelian inheritance pattern.

Quantitative traits like blood pressure are not determined by single gene. It usually results from multiple genes and their interaction. These multiple genes can be inherited to progeny in multiple ways and different progeny can have different combination of these genes. The differenc combination of these genes interact with one another to produce different traits. Thus it doesn't follow Mendelian inheritance pattern.

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