Chromosomal Mutations When Good Meiosis Goes Bad

MUTATION REVIEW Mutation is any change to a cell’s DNA Mutation is any change to a cell’s DNA - most mutations are bad - most mutations are bad – some can be beneficial – some can be beneficial - mutation is required for evolution to occur - mutation is required for evolution to occur Mutations can occur randomly 1 in 100,000 replications Mutations can occur randomly 1 in 100,000 replications Mutations can be caused by mutagens Mutations can be caused by mutagens

GENE MUTATION Mutations can occur in genes Mutations can occur in genes - point mutation – one nucleotide substituted for another - point mutation – one nucleotide substituted for another the fat cat ate the rat the fat car ate the rat - frameshift mutation – a nucleotide is either - frameshift mutation – a nucleotide is either inserted or deleted from a gene inserted or deleted from a gene - all of the DNA triplets from the point of mutation onward are altered. - all of the DNA triplets from the point of mutation onward are altered. deletion: the fat cat ate the rat the ftc ata tet her at deletion: the fat cat ate the rat the ftc ata tet her at insertion: the fat cat ate the rat the fan tca tat eth era t insertion: the fat cat ate the rat the fan tca tat eth era t

CHROMOSOME MUTATION Chromosome mutations occur when there is an error in meiosis Chromosome mutations occur when there is an error in meiosis chromosomes hold many genes – mutation has huge impact chromosomes hold many genes – mutation has huge impact can result in extra copies of entire chromosomes can result in extra copies of entire chromosomes can be changes to parts of chromosomes can be changes to parts of chromosomes

DIAGNOSIS A karyotype is produced to examine an individual’s chromosomes A karyotype is produced to examine an individual’s chromosomes - a karyotype is a picture - a karyotype is a picture of a person’s chromosomes of a person’s chromosomes as homologous pairs as homologous pairs - allows many - allows many chromosomal chromosomal mutations to be seen mutations to be seen

PRODUCING A KARYOTYPE Fluid is taken from the womb by amniocentesis Fluid is taken from the womb by amniocentesis -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 undergo mitosis. -the cells are grown in a tissue culture and induced to undergo mitosis. - they are treated making them easier to see and photographed in metaphase. - they are treated making them easier to see and photographed in metaphase. -pictures of homologous chromosomes are matched up and examined for mutations -pictures of homologous chromosomes are matched up and examined for mutations

NONDISJUNCTION Occurs when a tetrad fails to split in meiosis I Occurs when a tetrad fails to split in meiosis I or chromatids fail to split in meiosis II or chromatids fail to split in meiosis II

MORE NONDISJUNCTION Nondisjunction causes some gametes to receive an extra copy of a chromosome Nondisjunction causes some gametes to receive an extra copy of a chromosome – called trisomy – the zygote produced from this gamete will have 3 copies of the chromosome after fertilization – called trisomy – the zygote produced from this gamete will have 3 copies of the chromosome after fertilization - trisomy 21 causes Down Syndrome - trisomy 21 causes Down Syndrome Nondisjunction causes other gametes to receive Nondisjunction causes other gametes to receive no copies of a chromosome no copies of a chromosome - called monosomy –the zygote produced from this gamete will have only one copy of the chromosome after fertilization - called monosomy –the zygote produced from this gamete will have only one copy of the chromosome after fertilization -monosomy is usually lethal -monosomy is usually lethal

DELETION A portion of a chromosome is lost. A portion of a chromosome is lost. Deletions are responsible for many syndromes: Deletions are responsible for many syndromes: Cri du Chat, Wolf- Hirschhorn syndrome etc… Cri du Chat, Wolf- Hirschhorn syndrome etc…

INVERSION A segment of a chromosome will reverse end to end. A segment of a chromosome will reverse end to end. Most common on chromosome 9 – not harmful Most common on chromosome 9 – not harmful

DUPLICATION  a segment of a chromosome is duplicated producing extra copies of genes-on a chromosome.  can have harmful effects – Pallister-Killian Syndrome  can lead to new genetic combinations - potential force for evolution

TRANSLOCATION a part of a chromosome joins another non-homologous chromosome a part of a chromosome joins another non-homologous chromosome non- Robertsonian (balanced) – 2 non homologous chromosomes exchange parts – not harmful non- Robertsonian (balanced) – 2 non homologous chromosomes exchange parts – not harmful Robertsonian (unbalanced) – one chromosome gives up a part to a non-homologous chromosome – Down Syndrome Robertsonian (unbalanced) – one chromosome gives up a part to a non-homologous chromosome – Down Syndrome

NORMAL KARYOTYPES

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