1. Codominance, Multiple Alleles, Incomplete dominance, and Sex-linked Inheritance

2.  Not all alleles are dominant and recessive  Some alleles are equally strong and neither are masked by the other ◦ These alleles are said to be codominant  When both alleles are present in a heterozygote, they are both expressed in the phenotype  When expressing codominant alleles, both alleles are represented by different capital letters Example: Calico Cats = both black and orange spots are expressed, one is not dominate over the other

3.  A calico cat is crossed with a dominant orange cat. ◦ What colors will their kittens be?

4.  Remember: OB = female OO = male Kittens = calico (OB) and orange (OO) OOOB OOOB O O O B

5.  Multiple alleles: traits that are controlled by 3 or more alleles ◦ Example: human blood types  4 different blood types: A, B, AB, and O  3 different alleles: I A, I B, i  Codominance is also seen in blood types: when both phenotypes are expressed equally ◦ Example: AB blood type PhenotypeGenotype AI A I A or I A i BI B I B or I B i ABI A I B Oii

6.  A woman who is homozygous dominant blood type A marries a man who is homozygous dominant blood type B. ◦ What blood types could be found in their children?

7.  Remember: I B i = female I A i = male Offspring= blood type A (I A i), blood type B (I B i), blood type AB (I A I B ), and blood type O (ii) IAIBIAIB IAiIAi IBiIBiii IAIA i IBIB i

8.  The presence of a gene on a sex chromosome is called sex-linkage.  X-linked genes = genes found on the X chromosome  Can be found in BOTH males and females  Y-linked genes = genes found on the Y chromosome  Will be found ONLY in males

9.  Remember: XX = female XY = male (Y makes the guy!) X X X Y WHAT IS THE PROBABILITY OF HAVING A MALE OFFSPRING?

10.  In 1910, Thomas Morgan discovered traits linked to sex chromosomes in fruit flies.  Some genes are attached to the X and Y chromosomes  Examples of sex-linked traits: ◦ Red-green colorblindness ◦ Male pattern baldness ◦ Hemophilia ◦ Eye color in fruit flies

11.  In Men, traits expressed anytime present  In Women, must have two genes to show trait  Children inherit baldness from their mothers Sex-Linked Traits

12.  Example Problems: ◦ Red-green colorblindness is a recessive X-linked trait GenotypePhenotype Male – Not colorblind Male - Colorblind Female – Not colorblind Female – Not colorblind*** Female - Colorblind XNYXNY XnYXnY XNXNXNXN XNXnXNXn XnXnXnXn ***X N X n is a carrier. She does NOT exhibit the trait, but she CAN pass it on to her children.

13. PROBLEM 1: Normal vision father X Colorblind mother Will any of the children be colorblind?

14.  Remember: X n X n = female X N Y = male Children = Female carriers ( X N X n ), Colorblind Males (X n Y) XNXnXNXn XNXnXNXn XnYXnYXnYXnY XNXN Y XnXn XnXn

15. PROBLEM 2: Colorblind father X Normal vision mother (not a carrier) Will any of the children be colorblind?

16.  Remember: X N X N = female X n Y = male Children = Female carriers ( X N X n ), Normal Males (X N Y) XNXnXNXn XNXnXNXn XNYXNYXNYXNY XnXn Y XNXN XNXN

17.  Some alleles are not completely dominant over the other allele and an intermediate phenotype exists ◦ These alleles are said to have incomplete dominance  When both alleles are present in a heterozygote, they are both expressed in a combined phenotype ◦ A blending of the two alleles results  When expressing incomplete dominant alleles, both alleles are represented by the same letters Example: Pink carnations = neither white or red flowers are dominant so a blending occurs and the flowers are pink

18. If a pink carnation was crossed with a red carnation, will any of the offspring be pink?

19.  Remember: RW= female RR = male offspring = calico (OB) and orange (OO) RRRW RRRW R R R W