chromosomal mutations when good meiosis goes bad
TRANSCRIPT
Chromosomal Mutations
When Good Meiosis Goes BadWhen Good Meiosis Goes Bad
MUTATION REVIEW• Mutation is any change to a cell’s DNAMutation is any change to a cell’s DNA
- most mutations are bad - most mutations are bad
– – some can be beneficialsome can be beneficial
- mutation is required for evolution to - mutation is required for evolution to occuroccur
• Mutations can occur randomly 1 in 100,000 Mutations can occur randomly 1 in 100,000 replicationsreplications
• Mutations can be caused by mutagens Mutations can be caused by mutagens
GENE MUTATION
• Mutations can occur in genesMutations can occur in genes
- - point mutation point mutation – one nucleotide substituted for another– one nucleotide substituted for another
the fat cathe fat catt ate the rat the fat ca ate the rat the fat carr ate the rat ate the rat
- - frameshift mutation frameshift mutation – a nucleotide is either– a nucleotide is either
inserted or deleted from a geneinserted or deleted from a gene
- all of the DNA triplets from the point of mutation - all of the DNA triplets from the point of mutation
onward are altered.onward are altered.
deletion:deletion: the fthe faat cat ate the rat the ftc ata tet her att cat ate the rat the ftc ata tet her at
insertioninsertion:: the fat cat ate the rat the fa the fat cat ate the rat the fann tca tat eth era t tca tat eth era t
CHROMOSOME MUTATIONCHROMOSOME MUTATION
• Chromosome mutations occur when there Chromosome mutations occur when there
is an error in meiosisis an error in meiosis
• chromosomes hold many genes – chromosomes hold many genes –
mutation has huge impactmutation has huge impact
• can result in extra copies of entire can result in extra copies of entire
chromosomeschromosomes
• can be changes to parts of chromosomescan be changes to parts of chromosomes
DIAGNOSISDIAGNOSIS
• A A karyotypekaryotype is produced to examine an individual’s is produced to examine an individual’s chromosomeschromosomes
- a karyotype is a picture - a karyotype is a picture
of a person’s chromosomes of a person’s chromosomes
as homologous pairsas homologous pairs
- allows many - allows many
chromosomal chromosomal
mutations to be seenmutations to be seen
PRODUCING A KARYOTYPE• Fluid is taken from the womb by Fluid is taken from the womb by amniocentesisamniocentesis
-the fluid contains cells from the embryo-the fluid contains cells from the embryo
-the cells are grown in a tissue culture and induced to -the cells are grown in a tissue culture and induced to undergo mitosis.undergo mitosis.
- they are treated making them easier to see and - they are treated making them easier to see and photographed in metaphase.photographed in metaphase.
-pictures of homologous chromosomes are matched up -pictures of homologous chromosomes are matched up and examined for mutationsand examined for mutations
NONDISJUNCTION• Occurs when a tetrad fails to split in meiosis IOccurs when a tetrad fails to split in meiosis I
or chromatids fail to split in meiosis IIor chromatids fail to split in meiosis II
MORE NONDISJUNCTION • Nondisjunction causes some gametes to receive Nondisjunction causes some gametes to receive
an extra copy of a chromosome an extra copy of a chromosome
– – called called trisomy trisomy – the zygote produced from – the zygote produced from this gamete will have 3 copies of the this gamete will have 3 copies of the chromosome after fertilizationchromosome after fertilization
- trisomy 21 causes Down Syndrome- trisomy 21 causes Down Syndrome
• Nondisjunction causes other gametes to receiveNondisjunction causes other gametes to receive
no copies of a chromosomeno copies of a chromosome
- called - called monosomy monosomy –the zygote produced from –the zygote produced from this gamete will have only one copy of the this gamete will have only one copy of the chromosome after fertilizationchromosome after fertilization
-monosomy is usually lethal-monosomy is usually lethal
DELETIONDELETION
• A portion of a A portion of a
chromosome is lost.chromosome is lost.
• Deletions are responsible Deletions are responsible
for many syndromes:for many syndromes:
Cri du Chat, Wolf-Cri du Chat, Wolf-
Hirschhorn syndrome Hirschhorn syndrome
etc…etc…
INVERSIONINVERSION
• A segment of a A segment of a
chromosome will chromosome will
reverse end to end.reverse end to end.
• Most common on Most common on
chromosome 9 – not chromosome 9 – not
harmfulharmful
DUPLICATIONDUPLICATION
a segment of a a segment of a chromosome is duplicated chromosome is duplicated producing extra copies of producing extra copies of genes-on a chromosome.genes-on a chromosome.
can have harmful effects – can have harmful effects – Pallister-Killian SyndromePallister-Killian Syndrome
can lead to new genetic can lead to new genetic
combinations -combinations - potential potential force for evolutionforce for evolution
TRANSLOCATIONTRANSLOCATION
• a part of a chromosome a part of a chromosome joins another non-joins another non-homologous chromosomehomologous chromosome
• non- Robertsonian non- Robertsonian (balanced) – 2 non (balanced) – 2 non homologous homologous chromosomes exchange chromosomes exchange parts – not harmfulparts – not harmful
• Robertsonian Robertsonian (unbalanced) – one (unbalanced) – one chromosome gives up a chromosome gives up a part to a non-homologous part to a non-homologous chromosome – Down chromosome – Down SyndromeSyndrome
NORMAL KARYOTYPES
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