Genetic Anticipation

Question 1

This refers to the observation that in some diseases, there is a tendency for the age of onset of the condition to decrease & for the severity of the phenotype to increase, in successive generations.

Answer 1

Genetic anticipation

Question 2

T/F. The X - linked recessive condition, fragile X syndrome, exhibits pseudoautosomal inheritance .

Answer 2

False. Genetic anticipation

Question 3

Other diseases exhibiting genetic anticipation.

Answer 3

myotonic dystrophy

Huntington diseas

Several forms of spinocerebellar atrophy (SCA): currently SCA types 1, 2, 3, 6, 7, 8, 12, 17 and a complex form known as dentatorubral - pallidoluysian atrophy (DRPLA).

Question 4

Genetic anticipation is explained by ____ w/in or adjacent to a disease -associated gene and a tendency for the tract to become progressively larger by expansion at meiosis once it becomes ‘ unstable ’ by reaching a certain threshold size.

Answer 4

trinuclotide repeat expansion

Question 5

In the genes associated w/ Huntington disease and SCA (types 1, 2, 3, 6, 7 and 17), the ____ repeat tract is situated within the ____ itself, with an expansion therefore resulting in additional ____ amino acids within the encoded protein.

Answer 5

CAG; coding sequence; glutamine

Question 6

In the fragile X syndrome gene, the ___ repeat tract is located in the ____ w/ an expansion resulting in ____ and loss of function of the protein.

Answer 6

CGG; 5 ′ untranslated region (UTR); transcriptional repression

Question 7

In relation to myotonic dystrophy (type 1), however, the underlying ____ repeat expansion at chromosome ____ is located within the _____ of the ____ gene

Answer 7

CTG; 19q13; 3 ′ UTR; dystrophia myotonica protein kinase (DMPK)

Question 8

The mutant DMPK mRNA in myotonic dystrophy type 1 causes ____ (by sequestering important RNA - binding proteins) & thus exerts a toxic gain of function effect.

Answer 8

abnormal splicing of several genes

Question 9

A toxic gain of function RNA effect is believed to be involved in SCA8 in w/c a ____ expansion is present at the ____ of a non - coding RNA, in SCA12 in which a ____ tract is present in the ____ of the associated gene & in the relatively rare myotonic dystrophy type 2, which is now known to result from a ____ located within the first intron of the ____ gene at chromosome 3q21.

Answer 9

CUG; 3 ′ end; CAG; 5 ′ UTR; tetranucleotide repeat, CCTG, zinc finger protein 9 ( ZNF9 )