Chapter 13: Genes & Chromosomes

13.1 DNA: The Molecule of Heredity DNA is a nucleic acid made up of nucleotides each nucleotide made of sugar, phosphate & base 4 possible bases adenine, thymine cytosine, guanine

Chains of Nucleotides nucleotides form 2 long chains joined by hydrogen bonds DNA looks like a twisted ladder (double helix) organisms are different because their nucleotides differ in sequence

Replication of DNA process of copying DNA = replication enzyme unzips the DNA free nucleotides bond to each strand, following base pairing rules A-T, C-G process continues until whole molecule has been unzipped & replicated result = two identical DNA molecules

DNA to Protein the sequence of nitrogen bases along DNA strands code for proteins order of bases will determine amino acids mRNA goes into nucleus, copies message mRNA takes info to ribosomes, where proteins are made

13.3 Genetic Changes changes in DNA = mutations can be beneficial or detrimental point mutation = change in single base pair of DNA THE DOG BIT THE CAT THE DOG BIT THE CAR This is a substitution 1 letter (base) changed

changing single base can change entire protein

frameshift mutation single base added or deleted from DNA, shifting all bases THE DOG BIT THE CAT THE OGB ITT HEC AT Deletions and Insertions

Chromosomal Mutations occur in all living org’s, very common in plants gametes may end up with extra genes, or be missing some genes few chromosome mutations passed on to next generation zygote usually dies if zygote develops, usually sterile

Chromosomal Mutations Chromosomal mutations involve changes in the number or structure of chromosomes. These mutations can change the location of genes on chromosomes and can even change the number of copies of some genes. There are four types of chromosomal mutations: deletion, duplication, inversion, and translocation.

Chromosomal Mutations Deletion involves the loss of all or part of a chromosome.

Chromosomal Mutations Duplication produces an extra copy of all or part of a chromosome.

Chromosomal Mutations Inversion reverses the direction of parts of a chromosome.

Chromosomal Mutations Translocation occurs when part of one chromosome breaks off and attaches to another.

Errors in Disjunction nondisjunction = failure of homologous chrom’s to separate properly during meiosis trisomy = extra chromosome triploidy = 3 sets of chromosomes rare in animals, beneficial in plants monosomy = missing a chromosome

Examples of Nondisjunction Klinefelter’s syndrome – male with chromosomes XXY

Nondisjunction Examples Turner’s syndrome – female with chromosome X only (missing the 2nd one). Female should be XX Male is XY Individual w/ turner’s syndrome is just X

Causes of Mutations spontaneous mutations occur randomly mutations provide variation fundamental to evolution of species environmental agents can  mutations X rays, UV light, radioactive substances, chemicals

mutations often result in sterility, lack of normal development mutations in gametes may  birth defects mutations in body cells may  cancer agents that cause cancer = carcinogens