Females recessive traits are only expressed if both

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females recessive traits are only expressed if both X’s have the recessive gene for that trait (eg. Colour blindness) The Genetic Code and Gene Expression Structural genes are genes that contain the information necessary for the synthesis of proteins Proteins = long chains of amino acids; they control the physiological activities of cells and are important components of cellular structure All cells in the body contain exactly the same genes – then how do different kinds of cells develop? Because structural genes make up only a small portion of each chromosome Enhancers (or promoters) = stretches of DNA whose function is to determine whether particular structural genes initiate the synthesis of proteins and at what rate. They control gene expression which determines how a cell will develop and how it will function once it meets maturity. They are like switches and can react in 2 ways: can be turned up or can be turned down. Transcription factors: proteins that bind to DNA and influence the extent to which genes are expressed (these control enhancers and are often influenced by signals received by the cell from its environment) *** MECHANISM BY WHICH EXPERIENCE INTERACT WITH GENES TO INFLUENCE DEVELOPMENT*** Expression of Structural Gene First, small section of the chromosome that contains the gene unravels; the unraveled section of one of the DNA strands serves as a template for the transcription of a short strand of ribonucleic acid (RNA) (RNA is like DNA except contains nucleotide base uracil instead of thymine and has phosphate backbone instead of phosphate and deoxyribose backbone) The strand of RNA is called messenger RNA because it carries the genetic code out of the nucleus of the cell where it attaches to one of the many ribosomes in the cells cytoplasm. The ribosome moves along the strand of messenger RNA translating the genetic code as it goes. Each group of 3 nucleotide bases along the messenger RNA strand is called a codon. Each codon instructs the ribosome to add one of 20 different kinds of amino acids to the protein that it constructs. Amino acid is brought to the ribosome by transfer RNA; as ribosome reads a codon it attracts a transfer RNA molecule that is attached to the appropriate amino acid Certain codons code for stop indicating the protein is finished and it is released into the cytoplasm of the cell; thus gene expression involves 2 phases: the transcription of the
DNA base-sequence code to RNA base-sequence code and the translation of the RNA base-sequence code into a sequence of amino acids Mitochondrial DNA DNA located primarily in nucleus but the mitochondria (energy generating structure within cytoplasm of cell; including neurons) have DNA as well. Human mitochondrial genes are inherited solely from one’s mother Mutations develop here at a fairly consistent rate. Analysis of these mutations in human populations has added to the evidence that hominins evolved in Africa and gradually spread over the earth.

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