Ch.15 genetics ii
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Transcript of Ch.15 genetics ii
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Genetics - part two
Chapter 15
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Review
• Genes are located on chromosomes
• Diploid organisms have two copies of every chromosome
• Therefore, two alleles for every gene (except X,Y)
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Chromosomal basis of Mendel’s Laws
• Meiosis
• Segregation
• Independent assortment
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Fruit Flies
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Fruit Flies in Genetics
• Small genome – 4 chromosomes
• Short generation time
• Wild type – most common phenotype– Red eyes
• Studies revealed– Sex-linked genes
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Sex-linked Inheritance
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Gene Recombination & Crossing Over
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Constructing a Gene MapThe farther two genes are from each other, the higher the probability that crossing over will occur between them. This can be used to figure out where genes are on the chromosome.
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Some chromosomal systems of sex determination
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Sex-linked Inheritance
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Inactivation of the X & Barr Bodies• One X is inactivated during development – becomes Barr body• Same X is not inactivated in all cells• Mosaic in heterozygotes
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Nondisjuction (during Meiosis)
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Down Syndrome
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Genetic disorders caused by abnormal chromosome number (due to nondisjunction)
Name Chromosome Description
Down syndrome 21 Trisomy
Edward’s syndrome 18 Trisomy
Patau syndrome 13 Trisomy
Turner’s syndrome Single X XO
Klinefelter’s syndrome Extra X (in males) XXY
XYY syndrome Extra Y (in males) XYY
Triple X syndrome Extra X (in females) XXX
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Alterations of Chromosomes
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Genomic Imprinting
• Some genes behave differently if they come from ova/ sperm
• One gene can be “silenced” and the other is expressed
• Imprinting is not inherited
• Genes are re-imprinted for in the next generation
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Example: Imprinting• Prader-Willi/ Angelman syndromes• Deletion on chromosome 15
• If inherited from father– Prader-Willi syndrome
• Mental retardation, obseity, short stature, small hands and feet
• If inherited from mother– Angelman syndrome
• Spontaneous uncontrollable laughter, jerky movements, motor and mental problems