Describe two different ways that an error in meiosis could result in a human zygote that is missing one if its chromosomes (i.e., a zygote with 45 chromosomes instead of the normal 46).

Question

For each potential way this could happen, be specific about describing how and when the error would occur and describe the steps following the error all the way up to the zygote stage. 

Answer 1

The type of error that could occur is known as non-disjunction and this can occur in the anaphase stages of both meiosis I or II. Non-disjunction can cause either the duplication of a chromosome or the loss of one. Now remember, meiosis is the formation of the sex gametes. Each sperm and egg contains 23 chromosomes. At the point of fertilization, the zygote will have 46 chromosomes. If during meiosis I, the homologous chromosomes fail to separate (non-disjunction event), the result is two gametes that lack the chromosome and two gametes that have two copies of the chromosome. If the sister chromatids fail to separate in meiosis II, the results are one gamete that does not have the extra chromosome, two normal gametes with one copy of the chromosome, and one gamete with two copies of the chromosome.

Another possibility is an error that can occur during actual DNA replication - This error may lead to alternations within the sequence of the gene. Remember that any alternation disrupts gene function. Error during meiosis Introduces variation in the DNA sequence. The size of may be as small as a change to a single base or as large as the rearrangement of the whole chromosome. Error during DNA replication results in the wrong DNA nucleotide leading to the creation of muted protein. When the protein is mutated, this causes a change in its function. If meiosis does not occur properly, An egg or sperm contains too many chromosome or not enough chromosome.

Upon fertilization, in either case, the zygote will then either receive an extra chromosome or have a missing chromosome. Pregnancies with either trisomy(extra chromosome) or monosomy(missing a chromosome) can result in the birth of a child with a health problems or either miscarriage or stillborn birth.

Answer 2

The two ways errors during meiosis could result in a zygote with abnormal chromosome number is nondisjunction during either meiosis I or meiosis II. If homologous chromosomes fail to separate during meiosis I, the result is two gametes that lack that chromosome and two gametes with two copies of the chromosome. If sister chromatids fail to separate during meiosis II, the result is one gamete that lacks that chromosome, two normal gametes with one copy of the chromosome, and one gamete with two copies of the chromosome.