1. Meiosis & Mistakes
Chapter 10.2

2. Meiosis & Genetic Variation
Mitosis = identical cells
Crossing over in P1 of meiosis allows for genetic variation (different gene arrangements)
individuals can be unique

3. Genetic Recombination
Reassortment of chromosomes and genetic information they carry
by crossing over
or independent segregation
Each of the homologous chromosomes has an equal chance of being pulled to one cell versus the other

4. Mistakes in Meiosis Nondisjunction
Failure of homologous chromosomes to separate properly during meiosis
one cell will have an extra chromosome and the other cell will be missing a chromosome

5. Karyotype
Chart of chromosome pairs shows unusual numbers of chromosomes in cells
Shows if nondisjunction has occurred and chromosome disorders

6. Normally 46 chromosomes 23 pairs of two
All homologous except 23rd pair in males
Male: XY
Female: XX

7. Trisomy
a gamete with an extra chromosome is fertilized by a normal gamete, the zygote will have an extra chromosome
Example: Trisomy 21 (Down Syndrome)
Extra chromosome 21 (individual has 47 chromosomes)

8. Monosomy
Individual are missing a chromosome and have a total of 45 chromosomes
Most individuals with monosomy do not survive
Example: Turner’s syndrome
Human females have one X chromosome instead of two

9. Other Examples: Triploid
Occurs when an individual does not separate any of the homologous pairs
Gamete has diploid set of chromosomes
When fertilized with a normal gamete, the zygote will have three copies of each chromosome

10. Other Examples: Polyploids
more than the usual number of chromosomes (polyploidy)
Rare in animals
Frequent in plants
beneficial