Complex Patterns of Inheritance

1. Complex Patterns of Inheritance Unit 4 – Lecture 7

2. 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

3. Discuss • What does it mean to be “incomplete” ? [don’t say – to not be complete…think about this]

4. Incomplete Dominance • Incomplete Dominance • two dominant alleles present • BLEND of alleles is expressed when combined • 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. A 1

5. Incomplete Dominance – cont’d • Incomplete Dominance • ex: R = red, R1 = blue • RR = red • RR1 = PURPLE • R1R1 = blue • COLOR THE IMAGES ON YOUR LECTURE NOTES

6. 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.

7. 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

8. 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

9. 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 RR1 • R1R1 Rr • R1r rr red white white red AND white red orange

10. 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”

11. MA – Discuss • So…if A [IA] and B [IB] are dominant, and O [io]is recessive … • which genotypes will give each blood-type phenotype? [A, B, and O] • A blood: IA IA or IA io • B blood: IB IB or IB io • O blood: only io io

12. 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.

13. 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.

14. 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

15. 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

16. 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

17. 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

18. Naming Inheritance • Autosomal Recessive • affects males and females equally • traits often skip generations

19. 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.

20. 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