A student claims the probability a human sperm will receive all chromatids of maternal origin is 50 %. Explain why she is wrong.
To explain why the student's claim is incorrect, we need to understand the process of meiosis and how genetic material is divided during this process.
During meiosis, which is a specialized form of cell division that produces gametes (sperm or egg cells), the genetic material from the parent organism is divided into half and shuffled before being distributed into the resulting gametes. This division and shuffling process ensures genetic diversity in offspring.
To understand why the student's claim that a human sperm has a 50% chance of receiving all chromatids of maternal origin is incorrect, we should examine how the chromosomes segregate during meiosis.
In humans, each somatic cell (non-sex cell) contains 22 pairs of autosomal chromosomes and one pair of sex chromosomes (X and Y). During meiosis, the parent cell undergoes two rounds of cell division, resulting in four haploid cells (sperm or eggs), each containing a single set of chromosomes.
The first phase of meiosis, called meiosis I, involves the separation of homologous chromosomes. During this phase, each homologous pair of chromosomes (one inherited from each parent) lines up along the equator of the cell and then segregates into two separate daughter cells. This process is called "random assortment," meaning that chromosomes can segregate in different combinations, leading to genetic variation in the resulting gametes.
During meiosis II, the sister chromatids of each chromosome, which were replicated in the preceding S phase, separate. The two haploid cells produced from meiosis I divide again, resulting in four haploid cells, each containing one copy of each chromosome.
The point to note here is that the segregation of chromosomes during both meiosis I and meiosis II is a random process. It is impossible for a sperm to receive all chromatids of maternal origin because the chromosomes involved in the formation of a sperm do not favor any particular combination or arrangement. The distribution of chromatids among the sperm cells is a random and unpredictable event.
Therefore, the student's claim that there is a 50% chance of a human sperm receiving all chromatids of maternal origin is not based on the process of meiosis, which involves random assortment and segregation of chromosomes.