Lecture 17 Chromosome changes

Question 1

X chromosome inactivation in female
(what) inactivates X chromosome in female due to (what)

(when?)
(which?)
(in somatic cell vs in gamete formation)

Answer 1

Heterochromatin (tightly packed chromatin) formation inactivates an entire X chromosome in females due to dosage compensation (equal expression of X in both male and female)

when: early during development.
which: Random X-chromosome inactivation
inactivation is hereditary through cell division (reactivated in germ cell)

Question 2

Changes in chromosome number
Euploidy:
cause:
autopolyploid
allopolyploid

Aneuploidy:

Answer 2

Euploidy: complete sets of chromosomes
haploid (N): one set of chromosome
Diploid (2N): 2 sets of chromosome
Triploid (3N): 3 sets of chromosome
Tetraploid (4N): 4 sets of chromosome

cause:
auto: non disjunction of all chromosomes at meiosis
non disjunction at mitosis

autotriploid sterile, cant get complete set of chromosomes into one gamete.

allo: hybridization

Aneuploidy: loss or gain of one or more chromosome
Monosomy (2N-1): 1 chromosome in a homologous pair
Trisomy (2N+1): 3 chromosomes in a homologous pair
Tetrasomy (2N+2): 4 chromosomes in a homologous pair
cause: products of non disjunction at division one or two

Question 3

human chromosome mutations

Answer 3

Down syndrome: trisomy 21
Tuner syndrome: XO
Klinefelter syndrome: XXY