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    Punnett Squares on Human Blood Types, Mitosis, Meiosis, and Genetic Variability

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    Completed Punnett Squares and Answers to all Quest
    Details: Part 1: Genetics Problem - Human Blood Types

    Mendel is the father of modern genetics, but there are some genetic characteristics that cannot be explained by simple Mendelian genetics. Such is the case with the human blood types in which there are 3 alleles for the same gene, A B, and o. A parent can pass allele A, B, or o to the offspring based on the parent's genotype.

    From these 3 alleles, there are 4 blood types (phenotypes): A, B, AB, and O, and there are six genotypes: AA, Ao, BB, Bo, AB, or oo. This is an example of codominance in which both A and B alleles are codominant to each other.

    Blood types can be used in forensics to determine if blood is from the victim or criminal. Blood types can be used to determine parental source in situation where the father is unknown; however, blood types can only eliminate certain blood types. DNA fingerprinting is a better method that is used often in criminal and parental determination cases.

    Punnett squares such as the one shown above are used to determine the probabilities (percentages) for genotypes of offspring given specific genotypes for the parents.

    In the example above, the Punnett Square represents a cross (mating) between a male (on the left side) with blood type AB, and a female, (top of square), with blood type A, genotype Ao.

    Fill out and turn in the Punnett square for AB x Ao above. Answer questions for the cross represented above. Understand the difference between phenotype (blood type) and genotype. The Punnett Square shows the possible genotypes. When answering the questions, percent (probability) calculations and the response should be in terms of the phenotypes (the blood types) and NOT the genotypes.

    What are the possible blood types for the offspring?

    What are the ratios or percentages for each possible blood type from this cross?

    What blood type is not possible from this cross?

    Fill out two Punnett squares for a cross between a male with blood type B and a female with blood type AB. (Note that we do not know if the father is genotype BB or Bo from the information given. Thus there are two solutions to the possible cross.) Set up two Punnett squares and answer the following questions about them. Turn in these two Punnett Squares and your answers to the questions. Again, make sure you understand the difference between phenotype (blood type) and genotype. The Punnett Squares that you set up show the possible genotypes. When responding to the questions, percent (probability) calculations and your response should be in terms of the phenotypes (the blood types) and NOT the genotypes.

    What are the possible blood types for the cross between the type B (BB or Bo?) male and AB female?

    What are the percentages (%) or probabilities for each blood type in the offspring?

    What blood type(s) would not be possible in a cross between these two parents?
    Hint: There are two answers for questions 1 & 2 above and only one for 3.

    You will be turning in 3 completed Punnett squares and responses to the questions for Parts 1, A and B above.

    Part 2: Cell division, mutations, and genetic variability.

    Eukaryotic cells can divide by mitosis or meiosis. In humans, mitosis produces new cells for growth and repair. And, meiosis produces sex cells (gametes), called sperm and eggs. Changes or mutations in genes in sex cells can be inherited by human offspring. Genetic variation in a population of organisms is good; however, sometimes mutations can be harmful or cause genetic disorders.

    Briefly, answer the following two questions. List and cite your references for this:

    How do meiosis and sexual reproduction (fertilization) produce offspring that differ genetically from the parents? Be sure to talk about both meiosis and fertilization.

    Describe one example of a human disorder that is inherited and also describe the specific inheritance pattern. For this question, pick disorders that result from mutations in DNA or chromosome number rather than examples such as a genetic tendency for a disorder such as cancer.

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    Solution Preview


    Human ABO blood types are a great way to demonstrate codominant inheritance patterns and the use of Punnett squares to predict offspring phenotypic ratios. I am not sure what your background knowledge is so I will briefly review the following concepts:

    Genotype: The gene forms, or alleles, present for a given trait in an individual. Humans are diploid and thus have a pair (one from the mother and one from the father) of each of the 23 chromosomes that comprise our genome, for a total of 46 chromosomes. For ABO blood type systems we are talking about the physical genes that encode O-linked glycoproteins that act as antigens and are found on the surface of our red blood cells (for further information about this see http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/B/BloodGroups.html). Since we get one gene from our mother and one from our father, we have two of these genes. If the DNA sequences for these two genes differ, then we have different forms of the gene and glycoprotein products that also differ in amino acid sequence.

    Phenotype: The physical form or physiological state of an organism as coded by its genotype. For example, if your ABO blood cell genotype is AA, then your phenotype with respect to this trait is the A bloodtype. Note that one possible allele form for this gene is "O", which means no surface glycoprotein is ...

    Solution Summary

    This solution explains punnett squares on human blood types, mitosis, meiosis, and genetic variability.