Genetics

Question 1

What genes relevant to blood group antigens are on the X chromosome?

Answer 1

Xk, XG

Question 2

What is Lyonization?

Answer 2

Inactivation of an X-chromosome which occurs in women in development. Note: Some genes escape inactivation (eg. XG)

Question 3

Distinguish between heterozygosity and hemizygosity.

Answer 3

Heterozygosity: Two different alleles at a locus.
Hemizygosity: Only one allele at the locus (other deleted)

Question 4

What substance is used for G-banding?

Answer 4

Quinacrine

Question 5

What does it mean for genes to be “Syntenic”?

Answer 5

Being on the same chromosome but being sufficiently far enough for linkage disqeuilibrium to not occur.

Question 6

What does it mean for alleles to be in cis or trans?

Answer 6

Cis = Same chromosome (haplo)
Trans = Different chromosome (haplo)

Question 7

What is the position effect?

Answer 7

When one haplotype affects the expression of another. Example: Cappellini effect (Ce in trans to a D-containing haplotype reduces D expression).

Question 8

How does chimerism occur?

Answer 8

Can result from transplant, twin chimerism (in utero transfer of hematopoietic progenitors ONLY), or from tetragemeity/dispermy.

Question 9

What are some roles for DNA phenotype analysis?

Answer 9

Failure of serology to identify phenotype
Recent transfusion
Distinguishing alloantibodies from autoantibodies

Question 10

At what point in development can maternal cell-free DNA samples be used to determine fetal phenotype?

Answer 10

As early as 5 weeks, but ideally at 15 weeks or later.

Question 11

What antigens are best typed via genetics rather than serology?

Answer 11

Dombrock, Hy, Joa, Jsa, Jsb, Cw, V, VS