midterm

• Gene usually refers to a sequence of DNA that is transcribed into rna together with untranscribed regions that play roles in regulating its transcription
• locus technically refers to the chromosome site occupied by a particular gene but it is often used to refer to the gene itself
• true or false: thousands of genes in the human genome Encode ribosomal and transfer rnas that are translated into proteins

  false: NOT translated into proteins
• one strand of a protein-encoding gene is transcribed into rna, a process regulated by control regions: untranscribed sequences (enhancer and repressors) to which regulatory proteins produced by other genes bind
• a gene may have many different enhancer sequences
• after a gene is transcribed, the portions transcribed from exons are processed into a messenger RNA by splicing out the portions that were transcribed from introns
• mutation refers both to the process of alteration of a gene or chromosome and to its product, the altered state of a gene or chromosome
• mutation refer to an alteration of a gene from one form, or allele, to another, the alleles being distinguished by phenotypic effects
• mutation of chromosomes or genes are alterations that are subsequently replicated
• point mutation is a type of genetic mutation that involves a chance in a single nucleotide within a DNA sequence
• a point mutation can result in the substitution of one nucleotide for another, the insertion of an additional nucleotide, or the deletion of a nucleotide
• base pair substitution: a type of point mutation wherein one nucleotide is replaced by another
• transition (base pair substitution): substitution of a purine for a purine or a pyrimidine for a pyrimidine
• transversion (base pair substitution): substitution of a purine for a pyrimidine or vice versa
• frameshift mutation: a type of genetic mutation that results from the insertion or deletion of nucleotides in a DNA sequence
• unlike point mutations, which involve the substitution of one nucleotide for another, frameshift mutations alter the "reading frame" of the genetic code during translation
• synonymous mutation, also known as a silent mutation, is a type of point mutation that occurs in a gene without changing the amino acid sequence of the encoded protein
• nonsynonymous mutation: a type of mutation in a da sequence that results in the substitution of one nucleotide for another, leading to a change in the amino acid sequence of the encoded protein
• replication slippage is a molecular phenomenon that can occur during dna replication leading to the insertion or deletion of nucleotides in the newly synthesized dna strand
• replication slippage is more likely to occur in repetitive dna sequences, such as tandem repeats or microsatellites where the same sequence of nucleotides is repeated multiple times
• recombination typically is based on precise alignment of the DNA sequences on homologous chromosomes in meiosis
• when homologous dna sequences differ at two or more base pairs, intragenic recombination between them can generate new DNA sequences just as crossing over between genes generates new gene recombinations
• intragenic recombination, also known as gene or generic recombination, refers to the process by which genetic material is exchanged between two homologous dna sequences within the same gene
• intragenic recombination: this type of recombination can occur during the formation of gametes or in the repair of damaged dna
• unequal crossing over can occur between two homologous sequences or chromosomes that are not perfectly aligned. recombination then results in tandem duplication on one recombination product and a deletion on the other
• transposable elements often referred to as transposons or jumping genes, are dna sequences that can change their position within a genome.
• insertion sequences: relatively simple transposable elements consisting of two major components: a gene encoding a transposase enzyme and short inverted repeat sequences at their ends
• transposons: more complex than IS elements and can carry additional genes besides the transposase gene
• sickle-cell anemia: affects the shape of the red blood cells which carry oxygen to all parts of the body
• sickle-cell anemia is caused by a change from the (RNA) triplet GAA to GUA that causes the amino acid valine to be incorporated instead of glutamic acid
• cystic fibrosis: causes problems in the glands that produce sweat and mucus; results in thick mucus that clogs certain organs such as the lungs, pancreas, and intestines
• cystic fibrosis is caused by mutations in the gene encoding a sodium channel protein
• retinitis pigmentosa: degradation of the retina caused by mutations in genes on 8 of the 23 chromosomes in the human genome
• hemophilia: bleeding disorder in which the blood does not clot properly; caused by mutations in two different genes on 8 that encode blood-clotting proteins
• a-thalassemia: a severe anemia caused by the deletion of one of the loci of the two tandemly arranged genes for a-hemoglobin in case of unusual crossing over
• high cholesterol levels: caused by the lack of exon 5 in a low-density lipoprotein gene. this election has been attributed to unequal crossing over faciliatd by a short, highly repeated sequence called Alu that is located in the introns of this gene and many other sited the genme
• recurrent mutation refers to a genetic alteration that occurs repeatedly at the same specific location within a DNA sequence across multiple individuals or population
• in classical genetics, a mutation was detected by its phenotypic effects
• direct method (rates of mutation) - is to count the number of mutations arising in laboratory stock, scoring mutations either by their phenotypic effects or by molecular methods
• indirect method (rates of mutation) is based on the number of base pair differences between homologous genes in different species, relative to the number of generations that have elapsed since they diverged from their common ancestor