The cross between the male parent AB and female parent Ao revealed offsprings with genotype AA, Ao, AB and Bo. The gene pairs AA and Ao denote blood type A, the corresponding phenotype, AB denotes blood type AB for the offspring and Bo for blood type B. The given problem is a monohybrid cross. The phenotypic ratio or the blood type ratio is given to be 2 A: 1AB:1B. To express in percentages, this means that 50% or half of the total offsprings will acquire blood type A, 25% with blood type AB and remaining 25% for blood type B.
There is no chance of acquiring an offspring with blood type o since there is only one allele of o, that was provided by only the female parent only. For an offspring to have a blood type o, there must be an allele o from each of the parent that would combine at fertilization. In this case it is impossible to get a genotype oo, and so there is zero percent of probability of acquiring an offspring with blood type o. Figure 1 shows the completed Punnet Square for this cross.
On the other hand, the possible blood types or phenotypes for the cross of female parent with blood type AB and male parent with blood type B, assuming that the genotype is BB, are AB and B. This particular cross revealed a 50% probability of acquiring offsprings with blood type AB and also 50% for acquiring blood type B. It would be impossible to acquire offsprings with blood types A and o. This is because there is no chance of acquiring genotypes AA and oo.
Since there was be no provider of the allele o, so there would be no allelic pairing of o from both parents during fertilization. Note also that there is only one allele of A, that is provided by the female parent, however there is no A in the other parent and so it is impossible to have A and A pairing during fertilization. Figure 2 shows the completed Punnet Square for this cross. On the other hand, if we assume that the genotype of the male parent with blood type B is Bo, then the cross would reveal offsprings with blood type A ,B, and AB.
This cross also revealed that there is 50% probability of acquiring offsprings with blood type B with genotypes Bo and BB, 25% probability for blood type AB genotype is also AB and 25% probability of acquiring offsprings with blood type A with genotype Ao. Figure 3 shows the completed Punnet Square for this cross. This cross would not give offsprings with genotypes oo, which we know are the bood type o individuals. The reason again for this is there is only one allele of o, provided only by one of the parents and so no chances of o and o pairing of alleles.
It has been established that during fertilization, the genes exemplifying the same trait, for this example is the human blood type would pair up. There are different gametes that are being provided by the parents. These would talk on the Blood System on Humans, in this case we have the ABO blood group system in which the type is determined by the inheritanmce of one of the three alleles, the A, B and O (O’Neil 2007). There are three different alleles for the same gene.
Human blood type also displays codominance in nature, that is both the alleles A and B if both present in an individual will both manifest their effects on the individual (Mclean, 2000). It is contrasted to dominance and recessive alleles in which the allele which is more dominant to the other will mask out the effect of the other recessive allele (McLean, 2000) It has also been noted that human blood sampling is not accurate in forensics, rather DNA fingerprinting is more used. Answers to Part 2: Cell division, mutations, and genetic variability.
Meiosis is the process of joining the haploid chromosomes from each of the parents. Each chromosome on one parent has a homologous chromosome from the other parent. At syngamy, wherein the sex cells of the parents fuse, resulting to fertilization, the homologous chromosomes finally combine. The behavior of these chromosomes during the fertilization and meiosis accounts for the variation of the each generation. It was noted that there are three accountable mechanisms in which we can attribute genetic variation (Campbell, 1999).
The first one is the crossing over stage of the homologous portion of the chromosomes that are non-sister chromatid at the pachytene stage in very early Prophase 1. This is because the chromosomes pair up gene by gene, in which they trade a piece of the chromosome to the other forming what we call as chiasma. Crossing over stage is a very important stage in which the DNA inherited from the parents are being joined together in a chromosome. This is also refered to as recombination. The resulting individual with these chromosomes will be genetically different from the parents.
This explains why children look different from their parents (Lester cited by Ashcraft, 2004). The second one is the Independent Assortment of Chromosomes. This was first observed by Mendel. This reiterates that chromosomes at anaphase assort independently of the other during metaphase 1 which is a stage of Meiosis 1. The homologous chromosomes that were formerly bivalent independently segregate from each other. As a result, the first meiotic daughter cells could have a 50% chance of acquiring either the chromosome from the paternal or maternal parent.
After reaching the Telophase 1 of Meiosis 1, the daughter cells will then enter the Meiosis 2. Further independent segregation of the non-identical sister chromatids happen at Meiosis 2 (Biology Online, 2001). Random Nature of Fertilization also adds genetic variability from Meiosis. Considering the fact that any gamete of the male parent( sperm) could fertilize and fuse with the gamete of the female parent, that is in assumption that both gametes are viable, this could only mean that the formed zygote could contain any one in the million possible combinations of chromosomes.
It has been established that the ovum is one of the more than eight million possible combinations of the chromosome, and the same instance in the sperm (Campbell, 1999). There are any other factors that could be considered in the genetic variability of the offsprings from the parents, among which are linkage of genes inherited from the parents, chromosomal aberrations and viability of the gametes. A good example could be the genetic mutations. Take an instance that the parent could have accidental errors in the process of transcription, translation.
Our knowledge on DNA replication suggest that that our genetic material would propagate this mutation as the DNA make copies of itself. DNA replication make exact copies of theirselves, thus transferring the acquired to their next line of generation. These would be transferred in the gametes via meiosis, as we know meiosis is the mechanism for gamete formation. Fertilization of these gametes would then development new offspring with different genetic constitution as compared to the parents (Biology Online, 2001).
References Ashcraft, C. (2004). Genetic Variability by Design. Retrived August 06, 2008 from http://www. nwcreation. net/articles/recombinationreview Biology-Online-Scientific American. 2001. Independent Assortment and Crossing Over. Retieved August 8,2008 from http://www. biology-online. org/2/2_meiosis Campbell, N. (1999). Biology. Menlo Park: Benjamin/Cummings Pub. Co. McLean, P. (2000). Variations to Mendel’s First Law of Genetics. Mendelian Genetics. Retrived August 10, 2008 from http://www. ndsu. nodak. edu/instruct/mcclean/plsc431/mendel/mendel2. htm O’Neil. (2007). ABO Blood Types. Updated April 03, 2007. Retrived August 10, 2008 from http://anthro. palomar. edu/blood/ABO_system. htm