1. How many genes on each chromosome? hundreds
What would happen if a pair of chromosomes were broken or missing? It may affect a lot of genes
During meiosis (sex. Reproduction), chromosomes go to daughter cells.

2. However, sometimes mistakes happen.
Down Syndrome
Karyotype: normal human karyotype has 46 total chromosomes, or 23 pairs
Notice # 21 has an extra chromosome

3. (described syndrome in 1866)
Trisomy 21: a karyotype that includes three number 21 chromosomes
Down Syndrome:
John Langdon Down
(described syndrome in 1866)
Physical & other features:
Distinct facial features
heart defects
an impaired immune system
varying degrees of mental disability

4. Non Disjunction: homologous chromosomes or sister chromatids failing to separate during meiosis
As women get older, chances of DS increase.

5. Damaged Chromosomes 4 Types
Duplication - change to a chromosome in which part of the chromosome is repeated
Deletion - change to a chromosome in which a fragment of the chromosome is removed

6. Inversion - change to a chromosome in which a fragment of the original chromosome is reversed
Translocation - change to a chromosome in which a fragment of one chromosome attaches to a nonhomologous chromosome