LESSON #1.8: SEX-LINKED TRAITS, PEDIGREE CHARTS, MULTIPLE ALLELES

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 male genotypes: female genotypes: X A Y, X a Y a = recessive X A X A, X A X a, X a X a

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: C = c = Colour-blindness in humans NOT colour blind Colour blind

SAMPLE PROBLEM 1: Parent phenotypes: Colour-blind x not colour-blind Parent genotypes: X c Y x X C X C Parent gametes: X c Y x X C X C

SAMPLE PROBLEM 1: F 1 X c Y X C X C

SAMPLE PROBLEM 1: F 1 X c Y X C X C X c X C Y X C X C X c X C Y F 1 Phenotypes: 100% of daughters are NOT colour-blind 100% of sons are NOT colour-blind F 1 Genotypes: 100% of daughters are X C X c 100% of sons are X C Y

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: X C Y x X C X c Parent gametes: X C Y x X C X c

SAMPLE PROBLEM 1: F 1 X C Y X C X c

SAMPLE PROBLEM 1: F 1 X C Y X C X C X C X C Y X c X C X c X c Y F 1 Phenotypes: 100% of females have normal vision 50% of sons are colour-blind, 50% have normal vision F 1 Genotypes: 50% of females are X C X C, 50% females X C X c 50% of males are X C Y, 50% males X c Y

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

1 2 I II 1 2 3 4 5 III 1 2 3

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 X A X A - normal; X A X a -carrier; X a X a -affected X A Y-normal; X a Y-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: I A = A antigen on the red blood cells I B i = B antigen on the red blood cells, = has neither antigen If everyone has two copies of these genes, there are six possible combinations (genotypes) :

ABO BLOOD TYPING I A I A I A i I B I B I B i both resulting in Type A blood both resulting in Type B blood I A I B 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 ( I A i ) and the father has blood Type B ( I B i ). Determine the possible genotypes and blood types (phenotypes) for their children TRAIT: blood types Parent phenotypes: Parent genotypes: (mother) (father) Type A x Type B I A i x I B i Parent gametes: I A i x I B i

SAMPLE PROBLEM 1: I A i I B i

SAMPLE PROBLEM 1: F 1 Phenotypes: 25% Type AB; 25% Type A; 25% Type B 25% Type O F 1 Genotypes: 25% I A I B ; 25% I A i (heterozygous); 25% I B i (heterozygous); 25% i i (homozygous recessive) I A I B I A I B I B i i I A i i i i

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 Parent phenotypes: (father) (mother) Type A + x Type O- Parent genotypes: I A I A ++ x i i - - Parent gametes: I A + I A + I A + I A + x i- i- i- i-

SAMPLE PROBLEM 1: i - i - i - i - I A + I A + I A + I A +

SAMPLE PROBLEM 1: F 1 Phenotypes: 100% Type A + F 1 Genotypes: 100% I A i +- I A + I A + I A + I A + i - I A i +- I A i +- I A i +- I A i +- i - I A i +- I A i +- I A i +- I A i +- i - I A i +- I A i +- I A i +- I A i +- i - I A i +- I A i +- I A i +- I A i +- **These will be DIHYBRID Crosses!!!

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