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Unformatted text preview: basis of inheritance. A testcross is a cross between an individual with a recessive phenotype and an individual whose genotype is unknown. For a more detailed explanation, see the PowerPoint presentation. Please see the Conceptual and Experimental Summaries for Chapter 3 on page 66.
This lecture outline was prepared from Genetics: Analysis and Principles, by Brooker, 2009 (3rd edition). It contains phrases and entire sentences taken verbatim from that source, and is in no way meant to represent original work by Mark Bierner.
I n fruit ﬂ ies, the allele for red eye color can be shown as Xw+ (the + indicates that it is the dominant, wild type allele) and the allele f or white eye color can be shown as Xw Females can be Xw+Xw+ (homozygous dominant with red eyes), Xw+Xw (heterozygous with red eyes and, therefore, carrier of the white eye color allele), or XwXw (homozygous recessive with white eyes) The gene does not exist on the Y chromosome, so males can be shown as either Xw+Y (hemizygous dominant with red eyes) or XwY (hemizygous recessive with white eyes Xw+Xw (red-eyed carrier female) x Xw+Y (red-eyed male) ---> from what we did cross these are the results we obtained 25% Xw+Xw+ red-eyed 25% Xw+Xw red-eyed 25% Xw+Y red-eyed 25% XwY white-eyed Xw+Xw (red-eyed carrier female) x XwY (white-eyed male) --- > what we didn't cross 25% Xw+Xw red-eyed 25% XwXw white-eyed 25% Xw+Y red-eyed 25% XwY white-eyed TEST CROSS ONLY VALIDATES WHAT WAS SUSPECTED FROM RESULTS OF THE SECOND (F1 X F1 CROSS). HAD THIS BEEN AUTOSOMAL RECESSIVE, THE RESULTS WOULD HAVE BEEN THE SAME. Autosomal Recessive: Let R represent a dominant allele for red eyes and let r represent the recessive for white eyes. A test cross similar to the preceding would be heterozygous x homozygous recessive: Parent 1 Rr x Parent 2 rr 50% Rr red-eyed 50% rr white-eyed 10...
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