1. What are the possible blood types for the offspring? A, B and AB 2. What are the ratios or percentages for each possible blood type from this cross? 50% chance for Type A, 25% chance for Type AB and 25% chance for Type B. 3. What blood type is not possible from this cross? Type O because in order to develop a probability for it, both parent genotypes should have at least one O allele. B. Cross between male with blood type B and a female with blood type AB: A B A B
B AB BB B AB BB B AB BB o Ao Bo Male Genotype BB Male Genotype Bo 1. What are the possible blood types for the cross between the type B (BB or Bo? ) male and AB female? The cross would result in blood types A, B and AB. 2. What are the percentages (%) or probabilities for each blood type in the offspring? For male genotype BB: 50% for Type AB and 50% for Type B. For male genotype is Bo: 50% for Type B, 25% for Type AB and 25% for Type A. 3.
What blood type(s) would not be possible in a cross between these two parents? Type O because in order to develop a probability for it, both parent genotypes should have at least one O allele. PART II 1. How do meiosis and sexual reproduction (fertilization) produce offspring that differ genetically from the parents? Be sure to talk about both meiosis and fertilization. Meiosis is a two-phase process of cell division. In the male reproductive system, a primary spermatocyte which has 46 chromosomes goes through meiosis I to produce 2 secondary spermatocytes.
These in turn go through meiosis II to yield 2 spermatids each. In all, both phases result in 4 sperm cells which are unlike their parent cell because they contain just half the number (haploid or 23) of chromosomes (Tortora and Derrickson, 2006). In females, a primary oocyte completes the first round of meiosis on a monthly basis to yield a secondary oocyte with a haploid number of chromosomes. It also begins meiosis II prior to ovulation and completes this phase only after fertilization.
When a sperm fertilizes a secondary oocyte, the 23 chromosomes of the sperm combine with the 23 chromosomes of the oocyte to form a zygote with 46 (diploid number) chromosomes (Tortora and Derrickson, 2006). Rapid mitosis then takes place to produce an offspring that is different from each parent but bear resemblance to both parents since his/her set of characteristics are the result of the union of genetic material from both parents. The specific characteristics that will be fully expressed will be determined by the principles of inheritance as well as factors in the environment (Tortora and Derrickson, 2006).
2. Describe one example of a human disorder that is inherited and also describe the specific inheritance pattern. X-linked agammaglobulinemia or XLA is a congenital disease caused by mutations in the Bruton tyrosinase kinase (BTK) gene located on the X q21. 2-22 chromosome (Genetics Home Reference, 2008). BTK is an enzyme that is necessary for B-lymphocytes to mature and produce gammaglobulins or antibodies. The absence of BTK results in an individual with a severely depressed immune system, highly susceptible to infections.
XLA is sex-linked because mutations occur in a gene of the X-chromosome and presents in males because they only have one X chromosome (the other being the Y-chromosome) while females have two. Thus, females are not affected by the disease but only become carriers. What is striking about this disorder is that males cannot pass on the mutated gene to their offspring so that a 50% chance for sons inheriting the disease and for daughters to be carriers only occurs if the mother is a carrier (Genetics Home Reference, 2008).
List of References
Genetics Home Reference (2008). X-linked Agammaglobulinemia. Retrieved 23 October 08 from http://ghr. nlm. nih. gov/condition=xlinkedagammaglobulinemia. Starr, B. (2004). Understanding Genetics. Retrieved 23 October 08 from http://www. thetech. org/genetics/ask. php? id=199. Tortora, G. J. and Derrickson, B. (2006). Principles of Anatomy and Physiology 11th ed. New Jersey: John Wiley and Sons, Inc. University of Arizona (2004). The Biology Project: Blood Types Tutorial. Retrieved 23 October 08 from http://www. biology. arizona. edu/human_bio/problem_sets/ blood_types/Intro. html.