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)

Karyotype: A photomicrograph of chromosomes arranged according to a standard classification

What each of the human chromosomes look like

In other words… Chromosomes are digitally arranged so that they are matched with their homologue or “partner” chromosome. Homologue chromosomes are the same size, shape, and carry the same genes, and one is inherited from each parent. They are numbered according to size.

Sex determination with karyotype The first 22 pairs are autosomes Pair 23 are sex chromosmes— XX = female XY= male

Female and Male Karyotype

If there are chromosomal number abnormalities, how do they form? Meiosis: the process of creating sperm or egg from a diploid cell If there is a mistake when chromosomes are separating, then the resulting sperm or egg will have too many or too few chromosomes.

Prophase I: homologous chromosomes pairing into tetrads

Crossing over The chromosomes during prophase I undergo crossing over, where parts of the homologues randomly switch places.

Metaphase I: tetrads align, along the metaphase plate

Anaphase I: homologous chromosomes separate from the metaphase plate If chromosomes do not properly separate, this is called nondisjunction. Nondisjunction leads to trisomy and monosomy disorders.

Telophase I: membranes form around the separated homologues

Prophase II: spindle fibers bind to the sister chromatids of each chromosome

Metaphase II: chromosomes align along the metaphase plate

Anaphase II: sister chromatids separate to opposite poles

Telophase II: nuclear membrane forms around newly separated chromatids Note that each new nucleus formed has ½ the amount of DNA as the original cell. These cells are haploid cells.

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”

Nondisjunction

Disorders due to Nondisjunction In humans, a zygote with 45 chromosomes has only one copy of a particular chromosome monosomy In humans, a zygote with 47 chromosomes has three copies of a particular chromosome trisomy