Chromosome Theory of Heredity for Gene Mutations
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Presentation Transcript
10.1 The Chromosome Theory of Heredity • Chromosomes are located in the nucleus • Factors (genes) are found on chromosomes • Sutton discovered that genes are on chromosomes in 1902
Chromosome Theory of Heredity • States that genes are located on chromosomes and each gene occupies a specific place on a chromosome • Only one allele is on a chromosome
Gene Linkage • Genes on a chromosome are linked together • Inherited together – THEREFORE they do not undergo independent assortment
Linked Genes- genes on the same chromosome – inherited as a package Height Gene A Flower color gene B Flower position gene C
Linkage Groups • Package of genes that are always inherited together • Chromosome • One linkage group for each homologous pair
When they are lined up they can become twisted and switch genes Crossing Over
So you could then have ….. G G g g W w W w switch
Recombinants – individuals with new combinations of genes • Crossing Over – gives rise to new combinations – Prophase I
Sex Linkage • Stevens – made observations of meal worm chromosomes
Sex Chromosomes • One pair • Female – XX • Male – XY
Autosomes • All the chromosomes except the sex chromosomes
Genes on Sex Chromosomes • Sex chromosomes determine a person’s sex • Sex chromosomes also contain genes
Sex Linked • A gene located on a sex chromosome • Usually X • Example – Fruit Fly Eye Color • So the gene for eye color is on the X chromosome and not the Y
Fruit Fly Sex Chromosomes X X X Y
Males Females XRY XrY XRXR XRXr XrXr Red Eyed White Eyed
A change in the DNA of an organism • Can involve an entire chromosome or a single DNA nucleotide and they may take place in any cell
Germ Cell Mutation • Occur in an organism’s germ cells (gametes)- can only affect offpsring
Somatic Mutations • Take place in an organisms body cells and can affect the organism
Lethal Mutation • Cause death, often before birth
Good Mutations • Some mutations can be beneficial – these organisms have a better chance to reproduce and therefore have an evolutionary advantage • Provide the variation on which natural selection acts
Are either changes in the structure of a chromosome or the loss of an entire chromosome or an addition • Four Types (duplication, deletion, inversion and translocation)
Duplication – segment of a chromosome is repeated • Deletion – the loss of a chromosome or part due to chromosomal breakage – that information is lost
Inversion – a chromosomal segment breaks off and then reattached in reverse orientation to the same chromosome
Translocation – a chromosome breaks off and reattaches to another non-homologous chromosome
Nondisjunction • Some chromosome mutations alter the number of chromosomes found in a cell • Nondisjunction – the failure of a chromosome to separate from its homologue during meiosis
May involve large segments of DNA or a single nucleotide within a codon • Involve individual genes
Point Mutations – 3 types • The substitution, addition or removal of a single nucleotide
Substitution – a point mutation where one nucleotide in a codon is replaced with a different nucleotide, resulting in a new codon Ex. Sickle Cell Anemia – sub. Of A for T in a single codon
2 & 3. Insertion and Deletions – one or more nucleotides is lost or added – have more serious effects
Frameshift Mutation • When a nucleotide is lost or added so that the remaining codons are grouped incorrectly • Insertions and deletions are frameshift mutations
Polyploidy • Condition in which an organism has an extra set of chromosomes • 3N, 4N • Usually fatal in animals • Plants – usually more robust • Caused by - Nondisjunction
10-3 Regulation of Gene Expression • As biologists have intensified their studies of gene activity, it has become clear that interactions between different genes and between genes and their environment are critically important
