Presentation on theme: "February 23, 2009 Objective: Discuss the effects of nondisjunction"— Presentation transcript:
1 February 23, 2009 Objective: Discuss the effects of nondisjunction Drill:What is crossing over? What phase of meiosis does it occur?
2 NondisjunctionGT pg (Section 13.10) chromosomal mutation, p.408 (Last paragraph)?? Reg- p. 401, top 374
3 Review: What is a mutation? Mutation: A change in the nucleotide sequence of DNAA single nucleotide change can have serious effectsMutation: A change in DNAA single nucleotide change (insertion, deletion, substitution) could lead to the production of a different proteinA change in the nucleotide sequence of DNA (mutation) at even one location, can have serious effects.
4 Chromosomal mutationA chromosomal mutation involves a change in the structure or number of chromosomes4 types of chromosomal mutations:Deletion: loss of all or part of a chromosomeDuplication: extra copy of all or part of a chromosomeInversion: reverses the direction of parts of a chromosomeTranslocation: part of one chromosome breaks off and attaches to another chromosomeTranslocation- Found in a form of leukemia. Mutation called the Philadelphia chromosome- parts of chromosomes 9 and 22 break off and are translocated (exchanged position)
5 NondisjunctionOther types of chromosomal mutations alter the number of chromosomes found in the cell.Nondisjunction: The failure of homologous chromosomes or sister chromatids to separate during meiosis.Produces gametes that have too many or too few chromosomesNormal meiosisReg book: “not coming apart”
7 Disorders due to Nondisjunction In humans, a zygote with chromosomes has only one copy of a particular chromosome monosomyIn humans, a zygote with chromosomes has three copies of a particular chromosome trisomyExample Down syndrome (trisomy 21)
8 Nondisjunction in the Sex Chromosomes Nondisjunction can also affect the sex chromosomes, where there can be too many or too few X or Y chromosomes (XX- normal female, XY-normal male)Examples of disorders:XXY (Klinefelter’s syndrome)XO (Turner’s syndrome)
9 KaryotypeKaryotype: a picture of chromosomes in a dividing cell that are arranged in pairs by size.First 22 pairs are autosomesLast pair are the sex chromosomes