LESSON #1.8: SEX-LINKED TRAITS, PEDIGREE CHARTS, MULTIPLE ALLELES PART A: SEX-LINKED TRAITS • Sex-linked traits are controlled by genes located on the sex chromosomes. • A recessive trait located on the X chromosome is more likely to express itself in males A = Dominant a = recessive • male genotypes: XAY, XaY • female genotypes: XAXA, XAXa, XaXa PART A: SEX-LINKED TRAITS • A “Recessive lethal X-linked disorder” is a trait that when both recessive alleles are present it results in death/malformation of offspring (occurs more often in males) SAMPLE PROBLEM 1: In humans, the recessive allele that causes a form of red-green colour-blindness ( c ) is found on the X chromosome. • Identify the phenotypes and genotypes of the F1 generation from a colour-blind father and a mother who is homozygous for perfect vision. • Trait: Colour-blindness in humans • C = NOT colour blind • c = Colour blind SAMPLE PROBLEM 1: • Parent phenotypes: Colour-blind x not colour-blind • Parent genotypes: • Parent gametes: XcY Xc Y x x XCXC XC XC SAMPLE PROBLEM 1: F1 XC XC Xc Y SAMPLE PROBLEM 1: F1 Xc Y XC XCXc XCY XC XCXc XCY • F1 Phenotypes: 100% of daughters are NOT colour-blind 100% of sons are NOT colour-blind • F1 Genotypes: 100% of daughters are XCXc 100% of sons are XCY SAMPLE PROBLEM 2: • Identify the phenotypes and genotypes of the F1 generation from a father who has perfect vision and a mother who is heterozygous for colour-blindness. • Parent phenotypes: not colour-blind x not colour-blind • Parent genotypes: • Parent gametes: XCY XC Y x x XCXc XC Xc SAMPLE PROBLEM 1: F1 XC Xc XC Y SAMPLE PROBLEM 1: F1 XC Y XC XCXC XCY Xc XCXc XcY • F1 Phenotypes: 100% of females have normal vision 50% of sons are colour-blind, 50% have normal vision • F1 Genotypes: 50% of females are X CXC, 50% females XCXc 50% of males are XCY, 50% males XcY • WORKSHEET PART B: PEDIGREE CHARTS • Pedigree charts are constructed to show the inheritance of genetic conditions within generations of a family Fraternal twins Identical twins 2 1 1 I 2 II 3 4 1 5 2 3 III • Pedigree charts help in determining whether a trait is controlled by an autosomal dominant, autosomal recessive, or sex-linked allele • Autosomal dominant - if both parents have the trait and the offspring do not (“carriers” are not possible) AA-affected; Aa-affected; aa-normal • Autosomal recessive -if neither parent have the trait but some of their offspring do AA-normal; Aa-carrier; aa-affected • Pedigree charts help in determining whether a trait is controlled by an autosomal dominant, autosomal recessive, or sex-linked allele • Sex-linked- if only females are “carriers”; males and females show the trait unevenly XAXA- normal; XAXa-carrier; XaXa-affected XAY-normal; XaY-affected PEDIGREE CHART FOR THE SICKLE-CELL ANEMIA DISORDER: PEDIGREE CHART FOR THE SICKLE-CELL ANEMIA DISORDER: Conclusion: What can you determine about a family, using a pedigree chart? • # of generations/individuals • # of carriers • phenotypes/genotypes • # of individuas • whether it is autosomal dominant or recessive • WORKSHEET PART C: MULTI-ALLELISM • Some traits are controlled by two or more different alleles. This gives more possible phenotypes. **not to be confused with dihybrid crosses which involves two different traits; each controlled by their own alleles! ABO BLOOD TYPING • Your blood type is established before you are born, by genes inherited from your parents; you receive one blood type allele from each parent. • Your blood type is determined by alleles coding for the presence or absence of the Type A and Type B antigen molecules on the red blood cells. ABO BLOOD TYPING • the gene coding for blood type has three different alleles: IA = A antigen on the red blood cells IB = B antigen on the red blood cells, i = has neither antigen • If everyone has two copies of these genes, there are six possible combinations (genotypes) : ABO BLOOD TYPING IA IA IA i both resulting in Type A blood • IB IB • IB i both resulting in Type B blood IA IB resulting in Type AB blood (Type A & B are codominant) • i i resulting in Type O blood (recessive) ABO BLOOD TYPING ** A & B are codominant with each other, but dominant over i SAMPLE PROBLEM 1: Suppose that a mother has blood Type A ( IA i ) and the father has blood Type B ( IB i ). Determine the possible genotypes and blood types (phenotypes) for their children TRAIT: blood types • Parent phenotypes: (mother) Type A • Parent genotypes: • Parent gametes: IAi IA i x x x IB (father) Type B IBi i SAMPLE PROBLEM 1: IA IB i i SAMPLE PROBLEM 1: IA i IB IAIB IBi i IAi ii F1 Phenotypes: 25% Type AB; 25% Type A; 25% Type B 25% Type O F1 Genotypes: 25% IAIB; 25% IAi (heterozygous); 25% IBi (heterozygous); 25% i i (homozygous recessive) THE RHESUS FACTOR The rhesus factor is another antigen discovered on red blood cells; two possible alleles: • Rh-positive (Rh+) is dominant (~ 85% of Canadians have this antigen) • Rh-negative (Rh-) is recessive (15%) SAMPLE PROBLEM 2: For human blood type, the alleles for types A and B are codominant, but both are dominant over the type O allele. The Rh factor is separate from the ABO blood group and is located on a separate chromosome. The Rh+ allele is dominant to Rh-. • Indicate the possible phenotypes from the mating of a woman, type,O, Rh-, with a man, type A, Rh+ (both homozygous) SAMPLE PROBLEM 2: TRAIT: blood types and rhesus factor (father) • Parent phenotypes: Type A + • Parent genotypes: IA IA++ x x • Parent gametes: IA+ IA+ IA+ IA+ x (mother) Type Oi i- i- i- i- i- SAMPLE PROBLEM 1: IA+ iiii- IA+ IA+ IA+ SAMPLE PROBLEM 1: F1 Phenotypes: 100% Type A + IA+ IA+ IA+ IA+ i- IAi +- IAi +- IAi +- IAi +- i- IAi +- IAi +- IAi +- IAi +- i- IAi +- IAi +- IAi +- IAi +- i- IAi +- IAi +- IAi +- IAi +- F1 Genotypes: 100% IAi +**These will be DIHYBRID Crosses!!! Video and… PRACTICE TIME!