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Transcript
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