Chromosomes, Mapping, and the Meiosis–Inheritance Connection Chapter 13

2 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 History of Inheritance

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 3

4 Parental Generation

F 1 Cross 5

6 Testcross

7 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 2 X chromosomes = female 1 X and 1 Y chromosome = male Sex-linked trait “A trait determined by a gene on a sex chromosome”

8 X chromosome Y chromosome Human Chromosomes

9 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

10 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.

11 Genomic imprinting “Phenotype exhibited by a particular allele depends on which parent contributed the allele to the offspring”

12 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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14 Trisomy 18

15 Nondisjunction of sex chromosomes The result of nondisjunction of sex chromosomes is different than nondisjunction of autososomes.