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Blood Group Notes IB Assessment Statement • Describe ABO blood groups as an example of codominance and multiple alleles. Phenotype Genotype O ii A IAIA or IAi B IBIB or IBi AB IAIB Codominance • In the cases of some genes, two alleles may be expressed in the phenotype at the same time. • That is, NO allele is truly dominant or recessive. Codominance • When no alleles are dominant in a gene, we say these alleles are codominant. • Example: If a homozygous white rose (WW) is crossed with a homozygous red rose (RR) all their offspring are pink (WR). That ism they show a blending of physical traits. Blood Type. There are three alleles for blood type: • Blood Group B represented by IB – co-dominant with blood group A – Dominant over blood group O • Blood Group A represent by IA – co-dominant with blood group B – Dominant over blood group O • Blood Group O represented by i – Recessive to both group A and B Practice Cross 1 : • A person with homozygous Group A blood crosses with a homozygous Group B Blood: – The Symbols (letters you will use) ______________________ – The Cross (the parent’s genotypes)_________________________ – The Punnett square: Practice Cross 2: • A person with heterozygous Group AB blood crosses with another heterozygous Group AB Blood: • The Symbols (letters you will use) ______________________ • The Cross (the parent’s genotypes)_________________________ • The Punnett square: Practice Cross 3: • A person with heterozygous Group AB blood crosses with a person who has O type Blood: • The Symbols (letters you will use) ______________________ • The Cross (the parent’s genotypes)_________________________ • The Punnett square: Practice Cross 4: • A person with heterozygous Group A blood crosses with a person who is heterozygous with B type Blood: • The Symbols (letters you will use) ______________________ • The Cross (the parent’s genotypes)_________________________ • The Punnett square: IB Assessment Statement • Define sex linkage. IB Assessment Statement • Describe the inheritance of colour blindness and hemophilia as examples of sex linkage. – Both colour blindness and hemophilia are produced by a recessive sex-linked allele on the X chromosome. Sex-Linked Traits Notes __XX__= FEMALE ___XY__= MALE – There are some traits and genetic disorders that are carried on the Sex Chromosomes (usually the X)___. – There are many diseases are on the X chromosome • Examples: – Hemophilia – Color blindness • Genetic Disease are usually recessive. Genotype example – Examples: • __XN ___= normal gene • _ Xn _ = gene with trait or disorder IB Assessment Statement – State that a human female can be homozygous or heterozygous with respect to sex-linked genes. – Explain that female carriers are heterozygous for X-linked recessive alleles. MALES • Because males only have 1 X chromosome if they inherit the X chromosome with the disease on it they have the disease because they only have one X chromosomes to hide the trait. • Thus males inherit sex-linked genetic diseases more frequently than females. • ___XnY_____= male with trait • ___XNY__= male without trait FEMALES • Inherit 2 X chromosomes_ • Thus, females can also be a Carrier of the trait. This means even if a female does not have a disease, she can pass it to her offspring, if she is a carrier. –Xn Xn _= female with trait –XN Xn = female who is a carrier –XN XN= female without trait Example problem: • Colorblindness is a sex-linked trait. • Cross a carrier female with a normal male. – Select Symbols: – Write the cross: – Make a Punnet Square: IB Assessment Statement • Predict the genotypic and phenotypic ratios of offspring of monohybrid crosses involving any of the above patterns of inheritance • PRACTICE PROBLEMS