Mutations

Recall: DNA is made up of a sequence of nucleotides. A nucleotide is composed of a deoxyribose sugar, a phosphate group and a nitrogenous base. There are 4 bases in DNA - adenine (A), thymine (T), guanine (G) and cytosine (C). The order that these bases occur in the DNA that makes up your chromosomes is known as your genetic code. A series of bases that codes for a particular characteristic is called a gene. A change in the genetic code of an allele is called a mutation.

Mutations can be caused by… environmental agents such as damaging radiation certain chemicals errors during cell division A mutation may have a positive, negative, or neutral effect on the phenotype of the individual. Some gene mutations result in the new cell dying and being recycled. This is a lethal gene. However, sometimes cells carrying mutations survive and replicate. (induced mutations) (spontaneous mutations)

Point Mutations A point mutation occurs when the replicating cell fails to copy the genetic information accurately. There are three major point mutations: base-pair substitutions - one nitrogenous base is replaced with a different base insertions - one or more nitrogenous bases are inserted deletions - one or more nitrogenous bases are deleted

Ribosomes assemble proteins based on the DNA sequence. The ribosomes read the sequence in groups of three nucleotides – called a codon, which codes for a single amino acid. Amino acids combine to form polypeptide chains or proteins. If a change is made in the sequence of nucleotides, the ribosomes will read an altered sequence and possibly assemble a different protein.

Chromosome Mutations Errors that involve an entire chromosome or a large part of a chromosome can also occur. A mutation at this scale is known as a chromosome mutation. An example of a chromosome mutation is non-disjunction. Many mutations that do occur are immediately corrected during the copying process.

However, as organisms age, mistakes during mitosis occur more frequently and can lead to diseases such as cancer. Mutations that occur in somatic cells are not passed on to offspring. In contrast, mutations that occur in sex cells (gametes) can be passed on to offspring.

Transposons were first discovered in corn (maize) during the 1940s and ’50s by American scientist Barbara McClintock, whose work won her the Nobel Prize for Physiology or Medicine in Transposon are a class of genetic elements that can “jump” to different locations within a genome. When these ‘jumping genes’ change location, they disrupt how other nearby genes are expressed.

Homework: New Book: Read pg Questions p. 233 #2-4 and p.239 # 2,3,4,5a-c,7 Old Book: Read pg and complete p. 177 #1-5, 7 and p. 183 #1,2 Also write a brief description of the genetic disorders on pg 181 (Huntington’s, Cystic fibrosis, muscular dystrophy)