Lesson 2 Flashcards
is a unit of inheritance that encodes a particular protein, which is a key component of the human body
gene
Proteins from Genes
• ____(triplets of nitrogenous bases) code for specific amino acids.
• Amino acids link together to form____.
Codons
proteins
DNA and Chromosomes
• Genes are located in_____
• A double-stranded helix containing codons responsible for protein coding.
• \_\_\_\_: Coiled DNA structures found in the nucleus, containing 23 pairs: (2)
DNA
Chromosomes
• 1 pair of sex chromosomes (XX or XY) • 22 pairs of autosomes
• control metabolic processes within the cell, affecting tissues, organs, and body systems.
Chromosomes
Nitrogenous Bases
• (4)
• 3 consecutive nitrogenous bases
=____ (carries a specific amino acid).
• Amino acids link via _____to form proteins.
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
1 codon
peptide bonds
• Example: If a person has blood type A, their red blood cells express A antigens.
Phenotype
• The outward expression of genes.
• A result of genotype expression.
Phenotype
• The genetic makeup responsible for gene expression.
Genotype
Example Scenario:
• An individual with blood type B has B antigens on red blood cells.
• Possible genotypes: ???
• BB (homozygous)
• BO (heterozygous) → One dominant (B) and one recessive (O) gene.
T or F. Why??
• Two individuals can have the same phenotype but different genotypes.
• One could be homozygous (AA or BB).
• The other could be heterozygous (AO or BO).
• A & B are dominant genes → Antigens are expressed when present.
Genetic Principles in Blood Banking
Inheritance of Blood Type
• If both parents are heterozygous (AO and BO), their offspring can inherit different combinations of these genes.
• Possible genotypes for the offspring:????
• OO is…
• AB, AO, and BO are…
AB, AO, BO, OO.
homozygous (recessive)
heterozygous
Phenotype is determined by the____ expressed on red blood cells.
• A and B genes are dominant, so when both are present, both antigens are expressed →____
antigens
Type AB blood
Important tool for illustrating the probability of genotypes from known or inferred genotypes
Punnett square
• _____are located at specific____ (positions) on chromosomes.
• Example: ABO blood group gene is found on chromosome____.
Genes
loci
9
• Different forms of a gene at a specific locus.
Alleles
• ABO alleles:
• Each locus can only contain____ allele from each parent.
A, B, and O.
one
Blood Group System
ABO
Rh
Diego
Chromosome????
9 ABO
1 Rh
17 Diego
Antithetical
Allelic genes are_____, meaning only one form can be present at a given locus.
• Example: A, B, and O alleles—…
antithetical
each person inherits only one from each parent (either A B or O)
• Genes with multiple alleles at a single locus.
Polymorphic Genes
Polymorphic Genes
• Example:
• Rh blood group _____ alleles
• HLA (Human Leukocyte Antigen) has extensive variation, making organ matching difficult.
has 5 alleles (D, C, c, E, e).
Inheritance patterns: (3)
Codominant
Dominant
Recessive
Both inherited dominant genes are expressed.
AB blood type (both A and B antigens are expressed).
Codominant
A single dominant gene expresses its trait, even if paired with a recessive gene.
A or B blood type (AO or BO genotype).
Dominant
A recessive gene is only expressed if inherited in a homozygous state.
O blood type (OO genotype).
Recessive
Key Summary
• Dominant (A/B) + Recessive (O) →…
• Both Dominant (A & B) →…
• Both Recessive (O & O) →…
Antigen is expressed (Type A or B)
Both antigens are expressed (Type AB)
No antigen expression (Type O)
do not code for any functional product (e.g., antigens).
Silent, amorph, or null genes
Silent, amorph, or null genes
Causes (2)
- Inheritance of an amorphic gene from both parents (homozygous for a non-functional gene).
- Action of suppressor genes that inhibit gene expression, even if a dominant gene is present.
Example Scenario
• A person inherits a dominant gene (e.g., Lu^a/Lu^b for the Lutheran blood group),
• However, if a suppressor gene (In^Lu) is present, no antigen will be expressed, leading to a null phenotype (Lu a-b-).
Silent, Amorph, and Null Genes
There will be instances where despite inheriting a dominant gene, the inheritance of a suppressor gene will inhibit the expression of the products of a gene, regardless of inheriting
dominant genes = product of genes will not be expressed
Lutheran:
Dominant
Suppresor
Dominant gene: Lu a/Lu b
Suppressor gene: : In(Lu)
The amorph phenotype of the ABO blood group system
O
Null phenotype of Rh blood group
Does not allow the expression of DCcEe antigens
Rh null
Null phenotype
From the inheritance of both the recessive genes of the Lutheran blood group
Lu (a-b-)
are located at specific loci (positions) on chromosomes.
Genes
• Different forms of a gene at a specific locus.
Alleles
ABO alleles:
A, B, and O.
Allelic genes are______, meaning only one form can be present at a given locus.
• Example: A, B, and O alleles—each person inherits only one from each parent.
antithetical
• Genes with multiple alleles at a single locus.
• Example:
• Rh blood group has 5 alleles (D, C, c, E, e).
• HLA (Human Leukocyte Antigen) has extensive variation, making organ matching difficult.
Polymorphic Genes
Inheritance of an _______ gene from both parents (homozygous for a non-functional gene).
amorphic gene
Action of______ genes that inhibit gene expression, even if a dominant gene is present.
suppressor genes
• A person inherits a dominant gene (e.g., Lu^a/Lu^b for the Lutheran blood group),
• However, if a suppressor gene (_____) is present, no antigen will be expressed, leading to a null phenotype (Lu a-b-).
In^Lu
Kell
Amorph
Phenotype
K° (Silent Kell gene)
Kell-null (K0K0)
Lutheran
Amorph
Suppressor
Phenotype
Lu (Amorph Lutheran)
In(Lu)
Lu(a-b-)
Lutheran
Amorph
Suppressor
Phenotype
Lu (Amorph Lutheran)
In(Lu)
Lu(a-b-)
Kidd
Amorph
Suppressor
Phenotype
Jk
In(Jk)
Jk(a-b-)
Duffy
Amorph
Phenotype
Fy
Fy(a-b-)
ABO
Amorph
Phenotype
O
O
H
Amorph
Phenotype
h
Bombay
Bombay Phenotype
(hh)
Suppressor Genes in Blood Groups:
• → Even if dominant genes are present, these suppressor genes prevent antigen expression.
Lutheran (In^Lu) and Kidd (In^Jk)
Mendelian Principles in Blood Group Inheritance
- Independent Segregation (Law of Segregation)
- Independent Assortment (Law of Independent Assortment)
• Each parent has two copies of a gene but can pass only one allele to their offspring.
• The Punnett square demonstrates how each gene is transmitted independently.
Independent Segregation (Law of Segregation)
• Genes for different traits are inherited separately when located on different chromosomes.
Independent Assortment (Law of Independent Assortment)
ABO Chromosome
9
Kell Chromosome
7
Rh
Duffy
1
Lutheran
Lewis
LW
Hh
Chromosome
19
• _____genes do not produce any antigen → Leads to null phenotypes.
• _____genes inhibit antigen expression, even if a dominant gene is inherited.
Amorph (null)
Suppressor
Mendelian inheritance explains how blood group antigens are inherited:
• Independent segregation →______
• Independent assortment →_____
One allele from each parent.
Blood group genes on different chromosomes are inherited separately.
Understanding heterozygosity and homozygosity is crucial in blood banking because it affects the_______, which influences the strength of antigen-antibody reactions in serological testing.
dosage effect
Homozygous for Jk^a (Jk(a+b-))
Reaction Strength:
Strong (3+)
• Why? Because there is a double dose of Jk^a antigens, many antibodies can bind, leading to stronger hemagglutination.
Heterozygous for Jk^a and Jk^b (Jk(a+b+))
Reaction Strength:
Weaker (1+ to 2+)
• Why? Because the red cells contain both Jk^a and Jk^b antigens, there are fewer Jk^a antigen sites for the antibodies to bind, resulting in a weaker reaction.
• _____individuals have a mixed antigen population, leading to weaker serological reactions (1+ to 2+).
• _____individuals have a double dose of antigens, leading to stronger reactions (3+).
• Blood group antibodies can show dosage effects, meaning they react more strongly with homozygous cells than heterozygous cells.
Heterozygous
Homozygous
These concepts explain exceptions to Mendel’s Law of Independent Assortment, particularly when genes are located close to each other on the same chromosome.
Linkage, Haplotypes, and Crossing Over
are genes that are close together on the same chromosome and tend to be inherited together rather than independently.
• Example: MNSs blood group system
Linked genes
A_______ is the genetic combination of linked genes that are inherited as a unit.
• In the MNSs system, possible haplotypes are MS, Ms, NS, Ns instead of individual inheritance of M, N, S, and s separately.
haplotype
• Definition: When certain haplotypes occur more frequently in a population than expected by chance.
• Example: If genes were inherited separately:
• M = 17% of population
• S = 12% of population
• However, because M and S are linked, the MS haplotype might be found in 24% of the population instead of the expected (17% × 12% = 2%).
Linkage Disequilibrium
• Definition: When certain haplotypes occur more frequently in a population than expected by chance.
• Example: If genes were inherited separately:
• M = 17% of population
• S = 12% of population
• However, because M and S are linked, the MS haplotype might be found in 24% of the population instead of the expected (17% × 12% = 2%).
Linkage Disequilibrium
Crossing Over
• Occurs during cell division
(Prophase I of Meiosis)
• Exchange of genetic material between homologous chromosomes, leading to genetic recombination.
• Result: Creates genetic variation, making individuals unique—even identical twins!
Crossing over
close together on a chromosome are inherited together
MNSs blood group
Linkage Genes
Combination of linked genes that are inherited as a unit
MS, Ms, NS, Ns
Haplotype
When certain haplotypes appear more frequently than expected by chance
MS occurring in 24% instead of 2%
Linkage Disequilibrium
Calculations
This process is used to determine the frequency of a particular phenotype in a population,
helping to find compatible donor blood units for transfusion, ensuring that they lack certain antigens that could cause hemolytic transfusion reactions.
Combined Phenotypic Calculations
Gene Frequencies:
Hardy-Weinberg Equations
Hardy-Weinberg Formula
p^2 + 2pq + q^2 = 1
Hardy-Weinberg Formula
p^2 + 2pq + q^2 = 1
Where:
• ___= frequency of the dominant allele (homozygous)
• ___= frequency of the recessive allele (homozygous)
• ___= heterozygous genotype (combination of dominant and recessive alleles)
Also, it’s known that:
p + q = 1
p
q
pq
No longer appliacble
In the past, methods like blood typing were used for paternity testing to determine biological relationships. However, with advancements in DNA testing and molecular genetics, these older methods have become less reliable. Today, DNA testing is the most accurate way to confirm or exclude paternity.
Relationship Testing
No longer appliacble
In the past, methods like blood typing were used for paternity testing to determine biological relationships. However, with advancements in DNA testing and molecular genetics, these older methods have become less reliable. Today, DNA testing is the most accurate way to confirm or exclude paternity.
Relationship Testing
Paternity Testing Methods:
DNA testing
Blood typing
• Uses polymerase chain reaction (PCR) and other molecular genetics techniques to analyze genetic material and confirm or disprove paternity.
DNA Testing (Molecular Studies)
• Screening Test: Provides clues about paternity but is not a confirmatory test.
Blood Typing
Types of Paternity Testing:
- Direct Exclusion
- Indirect Exclusion
DE and ID are both dependent on the _____ gene
Obligatory gene
- expected to be passed on to the baby
• Definition: When the child’s genetic marker is absent from both parents.
Direct Exclusion
Example:
• Mother: Blood type O (OO genotype)
• Father: Blood type A (AA or AO genotype)
• Child: Blood type B (BO genotype)
• Explanation: The B marker in the child cannot be passed on by either parent (because the parents do not have the B allele), so______ occurs.
This means the man cannot be the biological father.
direct exclusion
Example:
• Mother: Blood type O (OO genotype)
• Father: Blood type A (AA or AO genotype)
• Child: Blood type B (BO genotype)
• Explanation: The B marker in the child cannot be passed on by either parent (because the parents do not have the B allele), so______ occurs.
This means the man cannot be the biological father.
direct exclusion
• Definition: When only one parent has the genetic marker, but the result might be influenced by other genetic factors (like a suppressor gene).
Indirect Exclusion
Example (using Kidd Blood Group system):
• Mother: Jk (a+b-) — Genotype: Jkª/Jka
• Father: Jk (a-b+) — Genotype: Jk’/Jkº
• Child: Jk (a+b-) — Genotype: Jkª/Jkº
• Explanation: The child’s blood type suggests the father should have passed on a Jk’ gene. However, if the father has a suppressor gene that inhibits the expression of the Jk’ antigen, the absence of Jk’ on the father’s side does not necessarily exclude him as the father.
This is termed______, as the suppressor gene could explain the lack of Jk’ expression.
Indirect Exclusion
