How many chromosomes should a “normal” human have? Are females XX or XY? How do the words: DNA, gene and chromosomes relate?

12.2: Chromosomal Disorders

Chromosomal disorders: Errors in the number or structure of a chromosome

Non-disjunction Homologous chromosomes or sister chromatids fail to separate during meiosis. Result: Gametes with abnormal # of chromosomes

Non-disjunction

Trisomy Having 3 of a particular chromosome. Examples Trisomy 21: Down syndrome Trisomy 18: Edwards syndrome - feet with rounded bottom - crossed legs, clenched hands

Trisomies of Sex Chromosomes XXX Female XXY: Klinefelter Male XYY: Male Turner’s Syndrome XO Female 45 Chromosomes

Chromosomal Duplications Part of a chromosome is repeated. Vary from fatal to developmental abnormalities. Often leads to cancer in somatic cells

Chromosomal Deletions Part of a chromosome is deleted. Ex: Williams Syndrome http://abcnews.go.com/2020/video/williams-syndrome-children-friend-health-disease-hospital-doctors-13817012 Partial deletion of chromosome 7

Chromosome Inversion Fragment breaks and reverses on the same chromosome. Not as lethal.

Chromosome Translocation Fragment of one chromosome attaches to ANOTHER, DIFFERENT chromosome. If there is an UNEQUAL swap of segments, results can serious. List of Chromosome Disorders http://www.netnet.net/mums/mum_chro.htm

Transposons Single genes that can move around. “Jump” from one chromosome to another. If they insert in the middle of an existing gene, that gene will be disrupted.