Chapter 13 Genes Chromosomes 13 1 DNA The

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 • m. RNA goes into nucleus, copies message • m. RNA 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 2 nd 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