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Transcript
Unit 4 – Lecture 7 Review Mendellian / Single-Gene Inheritance two alleles per gene = 1 dominant, 1 recessive ex: R = red, r = blue RR = red Rr = red rr = blue COLOR THE IMAGES ON YOUR LECTURE NOTES Discuss What does it mean to be “incomplete” ? [don’t say – to not be complete…think about this] Incomplete Dominance Incomplete Dominance two dominant alleles present BLEND of alleles is expressed when combined uses same letter with “prime” or 1 A another letter as exponent can have a recessive allele still – which is hidden by BOTH of the dominant alleles if present. Incomplete Dominance – cont’d Incomplete Dominance ex: R = red, R1 = blue RR = red RR1 = PURPLE R1R1 = blue COLOR THE IMAGES ON YOUR LECTURE NOTES Codominance Codominance two dominant alleles present BOTH alleles are expressed when combined offspring show both phenotypes at same time uses same letter with “prime” or another letter as exponent can have a recessive allele still – which is hidden by BOTH of the dominant alleles if present. Codominance – cont’d Codominance ex: R = red, R1 = blue RR = red RR1 = red AND blue [striped, spotted, checkered, etc] R1R1 = blue COLOR THE IMAGES ON YOUR LECTURE NOTES Multiple Alleles Multiple Alleles trait is coded for by more than 2 alleles for the SAME gene [same letter!!] more combinations for the same trait gene can have: multiple dominant alleles – like codominant or incomplete dominance multiple recessive alleles – all of which would be hidden by any dominant allele present MA Example - Discuss Example: three alleles for the “R” gene R = red R1 = white r = orange What color phenotypes would result from each of the following genotypes? [assume co-dominance] RR red RR1 red AND white R1R1 white Rr red white rr orange R1r Multiple Alleles – cont’d Multiple Alleles ex: Blood Type – codominant multiple allele trait alleles = IA, IB & io A and B are dominant, O is recessive caps letter “I” lower-case letter “i” MA – Discuss A B So…if A [I ] and B [I ] are dominant, and O [io]is recessive … which genotypes will give each blood-type phenotype? [A, B, and O] o A blood: IA IA or IA i B blood: IB I B o B I i or o o O blood: only i i NOTE You MAY NOT do blood type as your multiple allele trait. Your traits must ALL be able to be seen just by looking at your creature. Polygene Inheritance Polygene Inheritance “poly” = many traits are influenced by many genes will have combinations of different letters ex: traits with ranges or many types hair/eye/skin color, height, build, etc. Polygene Inheritance Polygene Inheritance ex: A / G / R = red a / g / r = no red more dominant alleles, more color Aa Gg Rr is darker red than Aa gg rr Naming Inheritance Types of Chromosomes Autosome = non-sex determining chromosome [1-22] “autosomal” trait = trait on a non-sex chromosome Sex-Chromosome = X or Y, chromosome pair #23 “sex-linked” trait = trait on the X or Y [sex] chromosome Naming Inheritance Autosomal Dominant dominant trait on a non-sex chromosome heterozygotes [Aa] and dominant homozygotes [AA] have the trait children with trait have at least one parent with the trait affects males and females equally Naming Inheritance Autosomal Recessive recessive trait on a non-sex chromosome must be recessive homozygote [aa] to have the trait children with trait have parents who either show or carry the trait carrier – heterozygote person for a recessive trait – does not show it, but has the allele [Aa] if both parents have the trait, ALL children will have the trait Naming Inheritance Autosomal Recessive affects males and females equally traits often skip generations Naming Inheritance Sex-linked Dominant [XA] dominant trait on a sex chromosome typically on the X-chromosome many are fatal [especially in males] if both parents have trait, most children will have it ¾ of children if heterozygous mother all children if homozygous mother affects males and females equally if both parents have it, all kids have it. Naming Inheritance Sex-linked Recessive [Xa] recessive trait on a sex-chromosome typically on the X-chromosome females can be carriers; males cannot affects more males than females son with trait can have parents who don’t show trait no father to son transmission of trait traits often skip generations