1. February 23, 2009 Objective: Discuss the effects of nondisjunction
Drill:
What is crossing over? What phase of meiosis does it occur?

2. Nondisjunction
GT 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 DNA
A single nucleotide change can have serious effects
Mutation: A change in DNA
A single nucleotide change (insertion, deletion, substitution) could lead to the production of a different protein
A change in the nucleotide sequence of DNA (mutation) at even one location, can have serious effects.

4. Chromosomal mutation
A chromosomal mutation involves a change in the structure or number of chromosomes
4 types of chromosomal mutations:
Deletion: loss of all or part of a chromosome
Duplication: extra copy of all or part of a chromosome
Inversion: reverses the direction of parts of a chromosome
Translocation: part of one chromosome breaks off and attaches to another chromosome
Translocation- 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. Nondisjunction
Other 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 chromosomes
Normal meiosis
Reg book: “not coming apart”

6. Nondisjunction

7. Disorders due to Nondisjunction
In humans, a zygote with chromosomes has only one copy of a particular chromosome monosomy
In humans, a zygote with chromosomes has three copies of a particular chromosome trisomy
Example 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. Karyotype
Karyotype: a picture of chromosomes in a dividing cell that are arranged in pairs by size.
First 22 pairs are autosomes
Last pair are the sex chromosomes

10. Karyotype A
* Normal male

11. Karyotype B * Turner’s syndrome
* Only 1 sex chromosome (X)- XO
* Webbed neck, short stature, and infertility
* Female

12. Karyotype C * Cri du chat syndrome
* Deletion of short arm of chromosome 5
* Distinctive cry, low birth weight, respiratory problems, may have a shortened lifespan
* Female
X Y

13. Karyotype D * Klinefelter’s syndrome * 2 X chromosomes and 1 Y (XXY)
* Tall, sterile, feminine characteristics, sometimes mentally retarded
* Male

14. Karyotype E
* Normal female

15. Karyotype F * Down syndrome * 3 copies of chromosome 21 (Trisomy 21)
* Mental retardation, characteristic facial features, short stature, and heart defects
* Male