Chromosomes and Mutations Dr. Nichols Coronado HS

What Are Mutations? Changes in the nucleotide sequence of DNA May occur in somatic cells (aren’t passed to offspring) May occur in gametes (eggs & sperm) and be passed to offspring

Are Mutations Helpful or Harmful? Mutations happen in many organisms regularly. Almost all mutations are neutral Chemicals & UV radiation cause mutations Many mutations are repaired by enzymes

Are Mutations Helpful or Harmful? Some type of skin cancers and leukemia result from somatic mutations Some mutations may improve an organism’s survival (beneficial)

Types of Mutations

Chromosome Mutations Five types exist: Deletion Inversion Translocation Nondisjunction Duplication

Deletion Due to breakage A piece of a chromosome is lost

Inversion Chromosome segment breaks off Segment flips around backwards Segment reattaches

Duplication Occurs when a gene sequence is repeated

Translocation Involves two chromosomes that aren’t homologous (the same) Part of one chromosome is transferred to another chromosomes

Translocation

Nondisjunction Failure of chromosomes to separate during meiosis Causes gamete to have too many or too few chromosomes Disorders: Down Syndrome – three 21st chromosomes Turner Syndrome – single X chromosome Klinefelter’s Syndrome – XXY chromosomes

Starting point

Real Life Deletions A portion of the chromosome is missing or deleted. Known disorders in humans include Wolf-Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4; and Jacobsen syndrome, also called the terminal 11q deletion disorder.

Real Life Duplications A portion of the chromosome is duplicated, resulting in extra genetic material. Known human disorders include Charcot-Marie-Tooth disease type 1A.

Types of Translocations Reciprocal translocation: Segments from two different chromosomes have been exchanged. Robertsonian translocation: An entire chromosome has attached to another at the centromere - in humans these only occur with chromosomes 13, 14, 15, 21 and 22

Diseases of Translocation Recurring miscarriages, Leukaemia, Infertility, Breast Cancer, Schizophrenia, Muscular Dystrophy.

Real Life Inversions Edwards syndrome: Ninety percent die in infancy; however, those that live past their first birthday usually are quite healthy thereafter. They have a characteristic clenched hands and overlapping fingers. Patau Syndrome, also called D-Syndrome or trisomy-13. Symptoms are somewhat similar to those of trisomy-18, but they do not have the characteristic hand shape.

Normal Male 2n = 46

Normal Female 2n = 46

Male, Trisomy 21 (Down’s) 2n = 47

Female Down’s Syndrome

Klinefelter’s Syndrome

Turner’s Syndrome 2n = 45

Introducing the chromosome!

Human chromosomes Image believed to be in the Public Domain

The chromosomes of a human female