1. When Meiosis goes wrong

2. Important terms Deletion Translocation Duplication Inversion
Non-disjunction
Monosomy
Trisomy
Prenatal
Karyotype

3. Learning goals To understand the ways that meiosis can go wrong
To be familiar with some of the more common genetic disorders that occur due to chromosomal malfunction

4. Review Meiosis is used to make gametes
When it works (and it usually does) each gamete ends up with a haploid number of cells (23 for humans
What do you notice about the 4 gametes?

5. Meiosis errors But sometimes it doesn’t go according to plan
Mistakes happen
There are two main types of errors
Errors caused by changes in chromosome structure
Errors caused by changes in chromosome number

6. Errors in chromosome structure
Usually occurs during the process of crossing over
Sometimes when parts of chromosomes detach and switch places, small pieces get removed or inverted (put in upside down)or switched to a completely different chromosome. Sometimes only one chromosome loses a piece and another chromosome gets one

7. Errors in Structure
When any of these things happen there is a chance that a baby that forms from one of the gametes will be deformed

8. Errors in Structure
Structural disorders can lead to many abnormalities and increase the likelihood of some diseases, including cancer
Table 4.1 on page 177 in your textbook describes some of these READ IT!!!!
Cri du chat
Syndrome is
a deletion
disorder

9. Errors in number
Occurs when homologous chromosomes or sister chromatids don’t separate properly in Anaphase (I or II)
This is called
nondisjunction

10. Errors in chromosome number
When non-disjunction occurs, one gamete will lose a chromosome and one will get an extra one
Both cases can cause defects
As you can see from the karyotype chart, the later chromosomes are shorter
Since they’re shorter, they’re more likely to get moved to the wrong place

11. Non-disjunction disorders
Trisomy – Down Syndrome-
Trisomy 18
-Edward Syndrome-
Cause – 3 chromosome #21
Chances – 1 in 800 births (more common with older mothers)
Signs- flattened face, intellectual disabilities, short stature
Cause – 3 chromosome #18
Chances – 1 in 18000
Signs- facial abnormalities, intellectual and physical disabilities

12. Non-disjunction of sex chromosomes
Klinefelter Syndrome
XXY
Turner Syndrome XO
1 in 1000 males
Unable to produce sperm
Female features (e.g. breast development)
1 in 5000 females
Short stature, webbed neck, sexual immaturity