22a) There would be 3 chromosomes present in each of the cells that make up the stomach of mosquito.
22c) There would be 3 chromosomes present in the sperm cells of a mosquito.
Prophase 1| A|
Metaphase 1| I|
Anaphase 1| E|
Telophase 1| F|
Prophase ii| H|
Metaphase ii| B|
Anaphase ii| G|
Telophase ii| d|
Prophase 1 is where the homologous chromosomes pair up and recombination occurs.
23) Non – Disjunction is the failure of chromosomes to separate properly. Non disjunction may occur during anaphase 1 or anaphase ii. If the tetrads do not separate normally during anaphase 1, an entire tetrad can end up on one side, therefore during the stages of meiosis ii gamates can be produced that either have extra chromosomes or are missing chromosomes. In the case of Down Syndrome the non disjunction has produced a gamete with an extra chromosome 21.
24a) Interphase 1 – there are three double stranded chromosomes, it is not a diploid because it does not contain 2 sets of DNA. The DNA in the nucleus has replicated the extra double stranded chromosome.
b) Anaphase 1 – The double stranded tetrads are pulled apart so that the chromosomes are separated to each pole, however one pole has an extra pair because of the extra set.
c) The nuclear membranes have reappeared and the spindle fibers have disappeared. One of the daughter cells is a haploid and one is not because of the extra chromosome.
D) Telophase II the daughter cells have split into 4, daughter cells contain the correct number of chromosomes and 2 others have an extra chromosome each.
25) There are a number important factors to consider in this answer. The first being is whether or not the non down syndrome parent is a carrier of the recessive down syndrome gene. If so it increases the chances that the couple will have a baby with down syndrome. As well, it needs to be researched, whether the parent with down syndrome, has down syndrome because of a mutation during meiosis or if it was a result of translocation. It the parent with down syndrome, has down syndrome because of the mutation during meiosis and the other parent is a non recessive gene carrier it is a very reasonable assumption that they will have a normal child, the odds are no higher for them than any other couple, because this type of down syndrome is not hereditary. If the other parent has a recessive gene or the down syndrome parent has the rare translocation, it increases their risk of having a down syndrome baby slightly higher than that of a couple who do not have down syndrome.
26) The general characteristics of a person with down syndrome include shorter height, mild to moderate intellectual ability and distinct facial features such as small upturned eyes, small flat noses a somewhat larger tongue and small ears. They also tend to have rounder flatter faces.
27a) Niemann Pick disease type A is a severe neurodegenerative disorder that occurs in infancy. This is an Autosomal Disorder. Generally by 6 months affected infants experience feeding difficulty, recurrent vomiting, enlargement of the spleen and liver which causes the abdomen to appear distended ( known as ascites) Some children with Niemann Pick Disease type A will have a cherry red spot in their retina. Affected children will only live to between 2 – 4 years of age, and there is no known cure or treatment for this disease.
B) The mothers genotype would be Ss, where S is the normal dominant sphingomyelinase gene, and s is mutated sphingomyelinase gene. Note to have Niemann Pick Type 2 disease you must have two SS genes.
C) The fathers genotype would be SS.
D) Father is SS, Mother is Ss