Errors in meiosis can cause genetic disorders

in humans and other eukaryotic organisms, meiosis is a type of cell division that produces germ cells. germ cells are egg cells in females and sperm cells in males. germ cells can contain defective genes that result in miscarriages or cause genetic disorders.
errors made by the cellular machinery during meiosis can lead to serious genetic disorders. some typical errors include incorrect copying of the dna sequence when the dna is replicated before cell division, errors during recombination, or errors when chromosomes segregate to the daughter cells.
if chromosomes fail to be separated and shuffled properly into the gametes during meiosis, an egg or sperm cell can have too many or too few chromosomes. this means that the extra chromosome will be passed down to the offspring and be present in every cell of the offspring's body. the word "trisomy" means that there are three copies of a chromosome, rather than just two—one from a person's mother and one from the father. trisomy 21, having three copies of chromosome 21, is commonly known as down syndrome. trisomy 21 is the most common chromosomal anomaly and affects about 5,000 babies born each year.
besides errors occurring in meiosis, genetic mutations in the fertilized embryo can be germline mutations or acquired mutations. sometimes, a mutation may occur in a person's germ cells but not occur in other cells. these mutations can be passed on to the person's children.
in another case, a mutation can occur in the germ cell right after the formation of the zygote. such mutations occurring in the embryo will manifest in all of the cells of the growing embryo. such mutations are called  de novo  mutations and explain why a child can have a mutation with no history of the mutation or the resulting disorder in their parents or other ancestors.
some types of mutations that occur early in the development of the embryo can result in two different forms of dna existing in the cells of the body. the different forms of dna occurring in the body are the result of cell division occurring before the mutation and after. this is known as  mosaicism, which is a condition that can cause health problems, depending on the mutation and how many cells are affected by the mutation. sometimes, genetic mutations can be so severe that they fatally disrupt embryonic development.
while many mutations can have serious consequences, other mutations have no noticeable effects on the individual's genome at all. a  silent mutation  occurs when one dna base in a protein-coding region is substituted for another that encodes for the same amino acid. for example, the stop codon taa located at the end of a protein coding sequence in dna could experience a single mutation in the third nucleotide, rendering it tag. the codon would still remain a stop sequence, so the function of the gene would not be affected.

reflect and respond

based on what you've learned, briefly explain the evolutionary significance of the fact that parents pass on their chromosomes to their children. what happens when there is an error in the mechanisms by which chromosomes are passed down? what are some genetic disorders that can arise from mutations that are either inherited or acquired?
a sample answer might look like this: parents pass on their chromosomes to their children because the dna, packaged in the chromosomes, provides the instructions for all cells in the body to function. if there is an error in the mechanisms by which chromosomes are passed down, the chromosomes may not be passed down properly. this could lead to genetic disorders. there are many examples of genetic disorders that range from very minor to very severe. a frameshift mutation causes tay-sachs disease, an autosomal recessive disorder that is typically fatal. frameshift mutations, in which the dna or rna sequence's reading frame is shifted by the addition or deletion of nucleotides, can have catastrophic consequences.