Transcript Chap. 13 Sex Linked Inheiritance_2

Chromosomes, Mapping, and the
Meiosis–Inheritance Connection
Chapter 13
History of Inheritance
• Carl Correns – 1900
– First suggests central role for chromosomes
• Walter Sutton – 1902
– Chromosomal theory of inheritance
• Carl Correns – 1909
– Suggests link between heredity and sex
• Thomas Morgan
– Fruit flies
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• T.H. Morgan – 1910
– Working with fruit fly, Drosophila melanogaster
– Discovered a mutant male fly with white eyes
– Wanted to see if this trait was inheritable
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Parental Generation
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F1 Cross
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Testcross
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Sex-Linked Traits
• Sex chromosomes:
– “The two chromosomes associated with an
organism’s determination of male or female”.
• Sex chromosomes vary according to species
• Drosophila sex is based on the number of X
chromosomes
•
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2 X chromosomes = female
1 X and 1 Y chromosome = male
• Sex-linked trait
• “A trait determined by a gene on a sex chromosome”
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X chromosome
Y chromosome
Human
Chromosomes
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Dosage compensation
• It would seem that since a female has two X
chromosomes, she should create twice as many
proteins as a male who has only one causing
another set of problems. But this doesn’t happen.
Why?
• Dosage compensation
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Chromosome theory exceptions
• The majority of inheritance comes from
the DNA in the chromosomes.
• Inheritance can also occur through the
DNA found in certain organelles.
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Genomic imprinting
• “Phenotype
exhibited by a
particular allele
depends on which
parent contributed
the allele to the
offspring”
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Nondisjunction of Autosomes
• “Failure of homologues or sister chromatids
to separate properly during meiosis”
• Aneuploidy – gain or loss of a chromosome
– Monosomy – loss of a chromosome
– Trisomy – gain of a chromosome
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Trisomy 18
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Nondisjunction of sex chromosomes
• The result of nondisjunction of sex
chromosomes is different than nondisjunction
of autososomes.
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