Basic Blood Bank Genetics

Question 1

How does genetics influence blood groups?

Answer 1

1. Different genes produce enzymes that add different types of sugars (ABO/ Lewis)
2. Different genes produce proteins which are found on the surface of RBC (Duffy system)

Question 2

Gene

Answer 2

a unit of heredity which is transferred from a parent to offspring and is held to determine some characteristic of the offspring

Question 3

Allele

Answer 3

one or two more alternative forms of a gene (one from mom and one from dad)

Question 4

Homozygous

Answer 4

Having two identical alleles of a particular gene or genes

Question 5

Heterozygous

Answer 5

Having two different alleles of a particular gene or genes

Question 6

Genotype

Answer 6

-the genetic composition of an individual organism

Question 7

Phenotype

Answer 7

-the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment

Question 8

Penetrance

Answer 8

the extent to which a particular gene or set of genes is expressed in the phenotypes of individuals carrying it
-measured in the proportion of carriers showing the characteristic phenotype

Question 9

Gene modifiers

Answer 9

-elements which affect the phenotypic and or molecular expression of other genes

Question 10

polymorphic

Answer 10

variants of a particular DNA sequence
-used in the setting of Rh blood groups

Question 11

haplotype

Answer 11

set of DNA variations, or polymorphisms, that tend to be inherited together
-used in the setting of Rh blood groups

Question 12

Cis

Answer 12

-when alleles occupy adjacent loci on the same chromosome

Question 13

Trans

Answer 13

-when alleles occupy adjacent loci on different chromosomes

Question 14

Mendel’s first law

Answer 14

shows that alleles of genes have no permanent effect on one another when present in the same plant but segregate unchanged by passing into different gametes

Question 15

Law of segregation (1st law)

Answer 15

-a diploid individual possesses a pair of alleles for any particular trait and each parent passes one of these randomly to its offspring

Question 16

autosomal dominant

Answer 16

-inheritance of dominant allele results in its phenotypic expression over a recessive allele

Question 17

autosomal co-dominant

Answer 17

-inheritance of two different alleles which results in the phenotypic expression of both alleles or partial expression of one allele

Question 18

autosomal recessive

Answer 18

-inheritance of two copies of a recessive allele or one amorph is required for the phenotypic expression of the allele

Question 19

Amorph

Answer 19

-mutated allele that has lost the ability to encode any functional protein

Question 20

Dominant (sex-linked)

Answer 20

-inheritance of the allele on the X or Y chromosomes results in full expression of the phenotype

Question 21

Co-dominant (sex-linked)

Answer 21

-inheritance of two different alleles on an X chromosome results in the phenotypic expression of both the alleles or partial expression of one allele

Question 22

Recessive (sex-linked)

Answer 22

-inheritance of the allele on the X chromosome resulting in all-male offspring expressing the trait and no females
-or the trait is expressed in all males inheriting the affected X chromosome or females inheriting two X chromosomes with the allele

Question 23

Codominance

Answer 23

-both alleles are expressed and their gene products are seen at the phenotypic level
-The homozygous type would have a stronger reaction than the heterozygous

Question 24

Dosage

Answer 24

significant difference in antibody reaction strength depending on the quantity of the target
-JKa JKb antigens will have a decreased quantity of each (single dose)

-JKa JKa antigens will have higher quantity and react stronger (double dose)

Question 25

Examples that show dosage

Answer 25

-Duffy
-Kidd
-Rh
-MNSs blood group systems

Question 26

Mendel’s second law (Law of independent assortment)

Answer 26

1. genes for different traits are inherited separately from each other
2. This allows for a possible combination of genes to occur in the offspring
3. Mendel’s law applies to all sexually reproducing diploid organisms

Question 27

Exceptions to Mendel’s second law

Answer 27

1. if genes for separate traits are closely linked on a chromosome they can be inherited together as a single unit

Question 28

Hardy-Weinberg Equation

Answer 28

p2+2pq+q2 = 1
-describes an idealized state
p = frequency of allele 1
q = frequency of allele 2

Question 29

What are the criteria that must be met in order to use the Hardy-Weinburg?

Answer 29

1. The population studied must be large
2. Mating must be random
3. No mutations in parents or offspring
4. No migration, no differential fertility, and no mortality of genotypes studied

Question 30

Phenotype frequencies

Answer 30

1. found by random testing of a population
2. independent phenotypes may be multiplied to give the frequency of the combinations in a population or the lack of the combination phenotype in the population

Question 31

Pedigree analysis

Answer 31

requires the understanding of various standard conventions in the representation of data figures
-males = squares
-females = circles
-Line joining a male and female indicates mating
-offsprings are indicated by a vertical line
- consanguineous mating is indicated by a double line

Question 32

Propositus

Answer 32

-the most interesting member of the pedigree indicated by an arrow

Question 33

Is inclusion certain

Answer 33

-never (but with genetic molecular testing it can be pretty close to certainly)

Question 34

is exclusion certain

Answer 34

-can be pretty certain in some circumstances but mutation is always a possibility

Question 35

Direct exclusion

Answer 35

when a genetic marker is present in the child but absent from both the mother and the alleged father

Question 36

Indirect exclusion

Answer 36

when a genetic marker is/are absent from the child that should have been transmitted by the alleged father given his observed phenotype

Question 37

What are the criteria for suitable markers?

Answer 37

1. well-established inheritance patterns
2. reliable phenotype determination
3. unhindered expression of the gene (co-dominant without modifier gene or null gene)
4. high frequency of common alleles
5. able to generate good probability of exclusion
6. many alternative alleles
7. gene frequencies established in the population in question

Question 38

Examples of suitable markers

Answer 38

ABO, Rh, MNSs, Kidd, Kell, Duffy, HLA, serum proteins, plasminogen, haptoglobin, transferrin, properdin B

Question 39

RFLP

Answer 39

restriction fragment length polymorphisms
-very robust system when used with at least 4 probes
-multiple probes and restriction endonucleases required as mutation is common and fragment length varies on both ends

Question 40

PCR

Answer 40

-used with HLA markers and VNTR and short tandem repeats
-pretty much the standard these days with 99% inclusion and 100% exclusion
-can now be done with pregnant women’s blood utilizing circulating fetal DNA