Question

You are a well-trained Cytogenetic Technologist. You work as a Genetic Counselor at a medical institution. You are meeting a nervous couple in your office, who recently found out that they are going to be first-time parents. They have come to you to discuss the chances of having a child with birth defect or genetic disorder. To ease their nerves, you greet them with a smile in your white coat, guide them to their seats, and slowly go through the options of prenatal tests available for them.

KARTOTYPE TEST METHODS
First you introduce to the parents the importance of karyotype test, by describing its domy to detect two broad categories of abnormalities in chromosomes, (1)_____and (2)_____. You provide a few examples of genetic disorders that can be caused by chromosomal abnormalities, such as (3)____and (4)____. Some parents would like to know what is the main cause of these genetic disorders. Without going into too much detail, you explain to them that chromosomal abnormalities are usually caused by (5)____in meiosis I and melosis II, when the homologous chromosomes or sister chromatids fail to separate during meiotic cell division
After the parents have decided to conduct a fetal karyotype test, you collect a small sample of chorion cells through chorionic villi sampling (CVS). Chorion is a membrane around the embryo that eventually fuses with the amnion. The chorion cells are grown in culture because chromosomes are most visible at (6)___stage of cell division. You use a technique called banding to create distinguishable landmarks on the chromosomes. There are several types of staining techniques you can use for karyotyping, some advanced techniques like FISH (fluorescent in situ hybridization) uses fluorescent probes to add colors onto different DNA sequences on the chromosome. You choose the most common type of staining techniques called G- banding to label the fetus chromosomes with Glemsa dye.
After taking photos of the chromosomes from a microscope, you sort the (7)____pairs of autosomes in the following order, from (8)____to (9)____, and keep the sex chromosomes last. The sorted photographed image of chromosomes is called (10)____. Now, you are ready to examine the karyotype of the fetus.

Answer 1

1 monosomy

2 trisomy

3 Down syndrome

4 Turner syndrome

5 non-disjunction

6 metaphase

7 twenty-two

8 largest (chromosome 1)

9 smallest (chromosome 22)

10 karyotype

Step-by-step explanation:

Non-disjunction during meiosis I or II occur when homologous chromosomes or sister chromatids refuse to separate. This makes the resulting gametes to have too many or too few chromosome numbers in their genomes.

A gamete with too few chromosome number that participates in fertilization with a normal gamete will result in a zygote with abnormally less chromosome number. This situation is referred to as monosomy. Whereas, the fusion of a gamete with too many chromosome number with a normal gamete will result in a zygote with too many chromosome, a situation known as trisomy.

The manifestation of monosomy and trisomy in humans results in Turner and Down syndromes respectively.

Humans have 23 pairs of chromosomes out of which a pair determines maleness or femaleness - the sex chromosome. Other chromosomes are referred to as autosomes. Hence, there are 22 autosome pairs and 1 pair of sex chromosome.

Chromosomes are studied by karyotyping, a process that involves photographing chromosomes at the metaphase stage of the cell cycle, cutting them out, and then arranging them in decreasing order of size.