1. Karyotypes Different organisms have different numbers of chromosomes Autosomes: Any chromosome that is not a sex chromosome (X or Y chromosome) – Humans have 22 pairs of autosomes Karyotype: a photograph of the complete diploid set of chromosomes grouped in homologous pairs and arranged in order of decreasing size.

2. How to make a karyotype: 1.Photograph a cell going through mitosis. – Why couldn’t you photograph a cell during interphase to make a karyotype? 2.Match up the chromosomes in homologous pairs. – What do a pair of homologous chromosomes have in common? – How are the chromosomes in a homologous pair different? 3.Arrange the chromosomes from largest to smallest Karyotypes

3. What can be learned from making a karyotype? – The number of chromosomes in the organism – The gender – The presence of chromosomal disorders What does the karyotype to the right tell you about the organism? Karyotypes

4. Chromosomal mutation: mutation that changes the number or structure of chromosomes (entire genes not just bases are changed). – Deletion: The loss of all or part of a chromosome – Duplication: A segment of the chromosome is repeated – Inversion: part of the chromosome is reverse from its usual direction. – Translocation: one chromosome breaks off and attaches to another chromosome. Chromosomal Disorders

5. Many chromosomal disorders are caused by a mistake in meiosis called nondisjunction. Nondisjunction: homologous chromosomes fail to separate during meiosis – Abnormal number of chromosomes find their way into gametes – Causes chromosomal disorders. – Which of the sperm cells have an extra chromosome, which are missing a chromosome? Chromosomal Disorders

6. Disorders caused by nondisjunction. Down Syndrome Caused by an extra 21 st chromosome. Also known as trisomy 21 Trisomy: having three copies of a chromosome. Chromosomal Disorders

7. Turner’s Syndrome Females are born with only one X chromosome Monosomy X: having only one X chromosome. Klinefelter’s Syndrome Males born with two X chromosomes and a Y chromosome. Y chromosome determines if the individual is male or female. Chromosomal Disorders