Lecture #22 - Non-human chromosomal abnormalities

Question 1

Define

1. Aneuploidy
2. Polyploidy
3. Other chromosomal aberreations

Answer 1

Aneuploidy - loss or gain of one or a few chromosomes relative to the diploid

Polyploidy - posession of multiple entire sets of chromosomes

Other chromosomal aberrations - loss, gain or rearrangement of parts of chromosomes

Question 2

Polyploidy

1. Self-fertilization can happen in what?
2. Can the autopolyploid be viable and fertile?
3. Why “auto”?

Answer 2

1. Can happen in plants
2. Yeah, can be becayse meiosis still works (every chromosome has a homologue) - may not (?) work for allopolyploids

Question 3

Just appreiciate because he gave nothing else

It’s fertile because?

Answer 3

Fertile because the homologous chromosomes can pair up at meiosis

But generally sterile because homologous chromosomes don’t match in prophase I meisosis - don’t recognise eachother

The two parents were co-incidentally from same family and so have same diploid no.

Question 4

Appreciate

Answer 4

Question 5

Also appreciate

Answer 5

Question 6

Appreicate

Answer 6

Question 7

Triploid parthenogenetic whiptail lizard Cnemidophorus neomexicanus

Answer 7

All offspring are female

No male in species

Mate with eachother to ovulate

Question 8

Discovery of tetraploidy in a mammal

Answer 8

Poliploidy in mammals is very rare - would mess up X Inactivation

Largest no. of chromosome in any mammal - know its polyplody bc all the close relatives of this rat have 1/2 amount of chromosomes in their nucleus

In this rat, some chromosomes have been lost and the whole set then doubled hence only one X and one Y (so has standard sex-determining as all mammals)

Question 9

Deletion, duplication, inversion and translocation

Answer 9

Deletion - piece of chromosome gets excised

Duplication - piece of chromosome duplicates - leads to evolutionary flexibility. The genes on duplicated get selected to do slightly different jobs

Translocation - could be due to crossing over. Two bits of non-homologous chromosomes swap over. Can be reciprocal if one off, other doesn’t have to give genes back.

Question 11

Lejeune syndrome

Cri du chat

Answer 11

Deletion of tip of short arm of chromosome 5

“crying of cat” - make this noise when young if affected

-Mental retardation, poor growth, eyes wide apart, 1 in 50k, 4:3 girs to boys

Question 12

William-Beuren Syndrome

Answer 12

deletion in chromosome 7

In graph: moving along chromosome 7 - missing those genes - slightly different deletion for these three people

Micro deletion in chromosome 8\7 - can be slightly different in different indiviuals - graph shows this so clinical effect different for different people.

Question 13

Inversions

Answer 13

Different populations have different inversions

Inversions cause problems in meiosis - chromosomes can’t line up in meiosis so can be identified in cell

Can have fertility effects

Question 14

Philadelphia translocation

Answer 14

Philadelphia translocation

t(9;22): 95% of patients with chronic myeloid lukemia

TK overexpression - treatable with Gleevec in 90% cases

Fused genes that are put together have tyrosine kinase - which keeps cells replication or something so it’s basically cancer

Question 15

Duchenne muscular dystrophy in a t(X;21) female

Answer 15

Usually lethal

Bad if normal chromosome has been inactivated - doesn’t have functional DMD gene.

Question 16

Familial Down Syndrome from t(14;21)

Answer 16

Familial down different to normal down bc it’s due to translocation - not nondisjunction.

Robertsonian translocation = two long arms of acrocentric chromosome fuse

Occurs in families - passed on

One of the gametes is 21/14 so essential 3 x 21 aka down normal