Genetic Disorders

Question 1

What is Down Syndrome caused by?

Answer 1

The individual has 3 copies of chromosome 21 which is caused by nondisjunction during meiosis.
Either the egg or the sperm has 2 copies instead of 1 of chromosome 21.

Question 2

What does sporadic trisomy mean?

Answer 2

It means the trisomy is not inherited

Question 3

True or False: You get 100% transfer over of genes

Answer 3

False, sometimes you don’t get 100% transfer over of genes

Question 4

What are two factors that impact how symptoms of Down Syndrome show in individuals?

Answer 4

Environment & genetic background

Question 5

List symptoms for Down Syndrome

Answer 5

• Intellectual Disability (100%)
• Congenital Heart Defect (40%)
• Hypotonia
• Atlantoaxial instability (neck) (12%)
• Hyperthyroidism/goiter (over active thyroid can cause metabolism issues & weight loss)
• Character facial features
• Increased incidence of Leukemia (1%)
• Male infertility
• Female significantly reduced fertility

Question 6

How can an extra chromosome cause a wide range of phenotypic effects?

Answer 6

• Chromosomes transmit genetic information

- The type & amount of genetic material is important for normal development

Question 7

Describe Tiploidy 69

Answer 7

In this syndrome you have a full extra set of chromosomes
-Usually caused by paternal chromosomes

• Not compatible with long term survival
• 2% of all conceptions
• 20% of all chromosomally abnormal miscarriages
• 3% of triploid conceptuses survive to be recognized
• Partial hydatidiform mole, usually associated with triploidy

Question 8

Describe the etiology of Triploidy 69

Answer 8

• No association with maternal age
• 69% are paternally derived due to double fertilization
• Remaining are failure of meiosis 2 resulting in diploid egg

Question 9

Explain why it is important that meiosis is a reduction division.

Answer 9

We need haploid gametes in order to live normal lives.

Question 10

What would occur to successive generations if it was not a reduction division?
Would this result in viable offspring?

Answer 10

Each generation would end up with excessive chromosomes

-No

Question 11

What does recurrent microdeletions & duplications result in?

Answer 11

nonhomologous recombination which results in unequal crossing over

Question 12

What is attributed to extra gene regions?

Answer 12

Phenotype

Question 13

Which disorder is associated with cat-eye syndrome?

Answer 13

Partial Tetrasomy 22q11

Question 14

Describe 22q11 syndrome

Answer 14

Highly variable-can be mosaic
Supernumerary marker chromosome involving two copies of 22q11
Symptoms include: cat-eyes
-down slanting palpebral fissures
-change in Iris and anal atresia with fistula

Question 15

What is a Dicentric chromosome?

Answer 15

A chromosome with 2 centromeres

Question 16

What is a derivative chromosome?

Answer 16

A chromosome that is composed of pieces from two or more chromosomes or has multiple chromosomal structural rearrangements within the same chromosome.

Question 17

What is a ring chromosomes?

Answer 17

A chromosome whose ends have fused together.

Question 18

What is a marker chromosome?

Answer 18

A chromosomal fragment that is too small to be identified by standard karyotyping, needs a specialized genetic analysis (Think sequencing)