Mendelian Genetics Notes

Mendelian Genetics Notes - Pedigrees Square male Circle...

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Pedigrees Square – male Circle – female Shaded – affected Open – not affected Ex. autosomal recessive (AR) assume that a person marrying into the family that is not affected is homozygous for the unaffecting allele double lines reflect inbreeding Is the trait recessive or dominant? - affected offspring with unaffected parents clue to recessive - both parents affected, but not all offspring affected clue to dominant Is the trait located on an autosome or on the sex chromosome? Is there a gender bias? 1. Y-linked – purely male to male transmissions (father to son only) 2. X-linked - recessive – affects male offspring more than females because females need two recessive X chromosomes to be affected - dominant – affects more females than males because fathers never pass x-linked traits to their sons 3. sex influenced – autosomal control influenced by sex hormones
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Ex. x-linked recessive x B x b x B y x B x B x b y x B x b x B y x B x b x B y x B x b x B y x B x b x b y x b y x b y x B x f8e5 x B x f8e5 x b x b presence of an affected females eliminates possibility that it is a y-linked trait gene passed from affected father via his unaffected daughter to his grandsons, therefore trait is x-linked recessive because first affected offspring came from unaffected parents Ex. Baldness B 1 = bald B 2 = nonbald Ex. genetics inheritance via mtDNA males females bald B 1 B 1 bald bald B 1 B 2 nonbald nonbald B 2 B 2 nonbald
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Mitochondrial DNA is passed in the cytoplasm during cytokinesis. Ova have a lot of cytoplasm, whereas sperm have very little. Therefore, mothers pass trait to all of their offspring and fathers pass to none. Ex. y-linked Ex. autosomal recessive (AR)
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3 1 2 Probability of 1 × 2 cross will be affected (dd): 1 2 × 1 × 1 4 = 1 8 P(1=Dd) P(2=Dd) Dd × Dd Probability of 1 × 3 cross will be affected (dd): _ 1 2 × 2 3 × 1 4 = 1 12
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Mendelian Genetics Notes - Pedigrees Square male Circle...

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