Mutation in Mitosis and Meiosis

Mutations can be: positive – have a good effect on the organism negative – be detrimental or fatal neutral – have no effect (repetition of triplet code)

If a mutation occurs in a gamete or during meiosis, the mutation is passed on to the offspring.

Mutations during DNA replication 1. base pair substitution/deletion (affects 1 amino acid) 2. frame shift mutation (affects every amino acid after mutation)

Mutations Due to Changes in Chromosomes 1. Nondisjunction - problems during meiosis which result in cells having too many or too few chromosomes - inheriting an extra chromosome results in a trisomy ex: Down Syndrome (trysomy 21) - a syndrome because it involves a group of disorders that occur together - mental impairment, thick tongue, short, stocky and thick neck - more susceptible to infection, heart defects, survive into 30’s and 40’s but have a higher risk of Alzheimer’s disease - genetic testing can tell a pregnant woman if the child will have Down Syndrome or not Changes in Chromosome Structure 2. Deletion - a portion of the chromosome is actually lost (caused by viruses, irradiation and chemicals) - example is cri-du-chat – a part of chromosome 5 is lost and the children have mental disabilities, an altered facial structure and a abnormally developed larynx that makes them sound like a cat when they cry

3. Duplication - when a gene sequence is repeated one or more times within one or more chromosomes - fragile X syndrome – 1 in 1500 males and 1 in 2500 females – 700 repeats instead of 29 of a specific gene

4. Inversion - a certain gene segment becomes free from its chromosome and is reinserted in the reverse order which of course alters gene activity

5. Translocation - part of one chromosome changes places with another part of the same chromosome or with a part of another non-homologous chromosome - if part of chromosome 14 exchanges places with a part of chromosome 8 cancer can occur - some of the Down Syndrome symptoms are related to translocations between chromosome 14 and 21, a type of leukemia is traced to translocation between chromosomes 22 and 9 Mutation Diagrams Mutation Diagrams