A student claims the probability a human sperm will receive all chromatids of maternal origin is 50 %. Explain why she is wrong.
Are the following true or false and support your answer:
i. Red blood cells and nerve cells in adult humans are suitable for karyotyping (determining the number, size, and morphology of the chromosomes)
ii. Polar bodies do not contain chromosomes.
iii. Immediately after meiosis I, cells are considered to be haploid.
iv. One tetrad/bivalent at metaphase I of meiosis consists of 2 non-identical strands of DNA.
To explain why the student is wrong in claiming that the probability of a human sperm receiving all chromatids of maternal origin is 50%, we need to understand the process of meiosis and how genetic material is divided during this process.
In meiosis, which is the type of cell division involved in the formation of gametes (sperm and egg cells), there are two main stages: meiosis I and meiosis II. During meiosis I, the homologous pairs of chromosomes are separated, while in meiosis II, the sister chromatids are separated.
In the process of meiosis I, the homologous chromosomes line up next to each other and can exchange genetic material in a process called crossing over. This exchange of genetic material results in a shuffling of the chromosomes, creating new combinations of maternal and paternal genetic information.
Based on this process, it is incorrect to claim that a human sperm will receive all chromatids of maternal origin. In fact, the genetic material in each sperm cell is a unique combination of maternal and paternal contributions due to crossing over during meiosis I. Therefore, the probability of a sperm receiving all chromatids of maternal origin is significantly less than 50%.
Now, let's analyze the statements and determine whether they are true or false:
i. Red blood cells and nerve cells in adult humans are NOT suitable for karyotyping. Karyotyping requires actively dividing cells, such as cells from the bone marrow, which can undergo cell division and provide a sample of chromosomes for analysis. Red blood cells and nerve cells are terminally differentiated cells, meaning they no longer divide, so they cannot be karyotyped.
ii. Polar bodies, which are produced during oogenesis, do NOT contain chromosomes. Polar bodies are formed during the asymmetric division of the cytoplasm in the process of oogenesis. They do not contain chromosomes because most of the genetic material is concentrated in the developing egg cell itself.
iii. Immediately after meiosis I, cells are considered to be haploid. This statement is true. After meiosis I, the resulting cells have undergone a reduction division, dividing the number of chromosomes in half. These cells are called haploid because they contain only one set of chromosomes, whereas the parent cell was diploid (containing two sets of chromosomes).
iv. One tetrad/bivalent at metaphase I of meiosis consists of 2 non-identical strands of DNA. This statement is true. During meiosis I, the homologous chromosomes pair up to form tetrads or bivalents. These structures consist of two non-identical strands of DNA, one originating from the mother and one from the father. The DNA within each strand can undergo crossing over, resulting in genetic recombination.