bb lec1 pt2

What is a gene?

A DNA segment inherited from parents that determines characteristics, including RBC antigens

What do genes determine in blood banking?

Antigens expressed on RBCs

What is a chromosome?

A nuclear structure that carries genes

Where are chromosomes located?

Inside the nucleus

What is mitosis?

Cell division in somatic (nucleated) cells

What is meiosis?

Cell division in gametes (sperm and egg)

How many chromosomes do gametes have?

23

How many chromosomes are present after fertilization?

46

What is phenotype?

Physical/visible expression of inherited traits

In blood banking, phenotype refers to what?

Antigen present on RBCs

What is genotype?

Actual genes inherited from parents

What determines phenotype?

Interaction of genotypes

Is phenotype interchangeable with antigen in BB?

Yes

What genotype produces blood type A?

A/A or A/O

Why does A/O still express A antigen?

A gene is dominant

What genotype produces blood type B?

B/B or B/O

Why does B/O still express B antigen?

B gene is dominant

What genotype produces blood type AB?

A/B

Why is AB codominant?

A and B genes are both expressed

What genotype produces blood type O?

O/O

What does the O gene represent?

Amorph (absence of A and B genes)

What is homozygous?

Same genes inherited (A/A, B/B, O/O, D/D)

What is heterozygous?

Different genes inherited (A/O, B/O, A/B)

Can AB be homozygous?

No, AB is always heterozygous

How should genotypes be written?

Italicized with a slash (e.g. A/O)

Can blood type O parents produce blood type AB child?

No

If both parents are A/O, what offspring blood types are possible?

A and O

If both parents are B/O, what offspring blood types are possible?

B and O

Can two blood type A parents produce a blood type B child?

No

What BB application uses ABO inheritance rules?

Paternity testing

What is the purpose of a Punnett square?

Predict genotype and phenotype probabilities

AO × AO produces what phenotypes?

75% A, 25% O

OO × AO produces what phenotypes?

50% A, 50% O

OO × AA produces what phenotype?

100% A

What is the most important Rh antigen?

D antigen

Why is D antigen important?

Most immunogenic Rh antigen

What genotypes express D antigen?

D/D and D/d

What genotype is Rh-negative?

d/d

What does small d represent?

Amorph (absence of D gene)

What does Rh-positive mean?

Presence of D antigen

What does Rh-negative mean?

Absence of D antigen

Can Rh-negative individuals have other Rh antigens?

Yes

dd × dd produces what Rh type?

100% Rh-negative

Dd × dd produces what Rh types?

50% Rh-positive, 50% Rh-negative

DD × dd produces what Rh type?

100% Rh-positive

Why is D antigen routinely detected?

It is the most exposed and immunogenic

Are other Rh antigens present but not tested?

Yes

What are alleles?

Alternative forms of genes at the same locus

What is a locus?

Location of a gene on a chromosome

How many genes can exist at one Rh locus?

2–3 genes

Example of Rh haplotype?

DCE/dce

What are antithetical antigens?

Opposite antigens produced by alleles

Example of antithetical pairs in Kell?

K and k

Example in Kidd system?

Jkᵃ and Jkᵇ

What is polymorphism?

Expression of multiple alleles at one locus

Which system is more polymorphic: Rh or ABO?

Rh

How many antigens exist in ABO?

4

How many antigens exist in Rh?

~50

Why is HLA highly polymorphic?

Many alleles at one locus

Which HLA belong to MHC Class I?

HLA-A, HLA-B, HLA-C

Which HLA belongs to MHC Class II?

HLA-D

Purpose of HLA typing?

Transplant compatibility

What is codominance?

Both genes expressed (e.g. AB)

What is dominance?

One gene suppresses another

What is recessive inheritance?

Expressed only if homozygous

Example of dominant suppression?

Leᵇ suppresses Leᵃ (Lewis)

What are the two types of silent genes?

Amorph and suppressor

What is an amorph gene?

Gene that produces no antigen

Example of amorph gene in ABO?

O

Example of amorph gene in Rh?

d

What are common Duffy genes?

Fyᵃ, Fyᵇ, Fy (amorph)

What phenotype is Fy(a-b-)?

No Duffy antigens expressed

Which population commonly has Fy(a-b-)?

African descent

What is a suppressor gene?

Gene that inhibits antigen expression

Example suppressor gene?

In(Lu)

Which system uses suppressor genes?

Lutheran

What is independent segregation?

One gene passed from each parent

What is independent assortment?

Genes on different chromosomes assort independently

Which systems are linked on chromosome 1?

Rh and Duffy

Which systems are linked on chromosome 19?

ABO and H

Which blood group is X-linked?

Xgᵃ

Which chromosome carries Xgᵃ gene?

X chromosome

Can males be heterozygous for Xgᵃ?

No

What is dosage effect?

Stronger antigen expression in homozygous inheritance

Which blood groups show dosage?

MNSs, Rh (except D), Duffy, Kidd, Lutheran

Why does D antigen not show dosage?

Expressed strongly in both homozygous and heterozygous

Why is dosage important in antibody detection?

Antibodies may react only with homozygous cells

Why can anti-M be missed?

M antigen weakly expressed in MN cells

Which reagent cells detect dosage antibodies best?

Homozygous reagent cells

What is cis position?

Genes on same chromosome

What is trans position?

Genes on opposite chromosomes

What is C trans?

C antigen masks D antigen

What results from C trans?

Weak D (Du variant)

What is weak D?

Reduced expression of D antigen

Why is weak D clinically important?

May be misidentified as Rh-negative

What causes weak D?

C trans, partial D, weak D gene

What is linkage?

Genes inherited together due to proximity

What is a haplotype?

Set of linked genes inherited together

Example haplotype?

DCE

What is crossing over?

Exchange of genes during meiosis