Genetics - Lecture 1 - Chromosome abnormalities in human diseases

What are the 2 types of chromosomal disorders?

1. Aneuploidy

2. Changes in chromosome structure

What are 3 example syndromes of aneuploidy (extra or lost chromosomes)?

1. Down syndrome (caused by trisomy 21 - 3 copies of chromosome 21)

2. Kinefelter syndrome (genotype of XYY - extra copy of chromosome Y)

3. Turner syndrome (X0 - they don’t have a second sex chromosome, one copy of chromosome X)

What does changes in chromosome structure refer to?

the right number of chromosomes but significant change in the arrangement or structure of one or more chromosomes

→ which can lead to various genetic disorders

what are the 5 types of changes in chromosome structure?

1. deletions

2. duplications

3. inversions

4. reciprocal translocations

5. robertsonian translocations

what is deletion in chromosome structure?

• removal of a segment of a chromosome

• results from deletion of an area of chromosomes called 5p - 5p deletion syndrome

what is duplications in chromosome structure?

• whole chunks of chromosomes appear twice

• either appear in the original spot - 2 bits next to each other in the same direction

• or they can translocate to another bit of the genome

what inversions in chromosome structure?

• chunk of chromosome that flips around

• the total amount of DNA is correct but the sequences at either ends of the inversion are near sequences that they shouldn’t be near

  → leads to impact

what is reciprocal translocations in chromosome structure?

• when two chromosomes swap some material

what is robertsonian translocations in chromosome structure?

• specific translocation that is more commonly seen

• one of the ways you can get down syndrome

what is aneuploidy?

• chromosome aberrations in which the chromosome number is abnormal (not a whole set)

• an aneuploid is an individual organism whose chromosome number differs from the wild type by the part of a chromosome set

• usually, the aneuploid chromosome set differs from the wild type by only one chromosome or by a small number of chromosomes

• aneuploid can have a chromosome number either greater or smaller than that of the wild type

what is polyploidy?

• organisms have more or fewer than the normal number of sets (aberrant euploids)

• polyploids are individual organisms that have more than two chromosome sets

• how many copies of all the chromosome an individual has relates to how many times we get the 23 chromosomes

  —> the number fo chromosome sets is called the ploidy or ploidy level

what are the 2 syndromes that can occur as a result of aneuploidy?

(normal chromosome number = 2n (2 copies) = 46 (23×2)

1. monosomy - missing chromosome (2n - 1 = 45)

2. trisomy - extra chromosome (2n + 1 = 47)