Genetics: Rhesus Factor and Inheritance

• These notes cover genetics, inheritance patterns, and blood groups.

The Rhesus Factor

• The Rhesus factor is another antigen inherited independently of the ABO blood group system.
• Inheritance is dominant-recessive.
• Genotypes: DD or Dd result in Rh-positive, dd results in Rh-negative.
• Phenotypes: Rh-positive or Rh-negative.
• Frequencies: 85% Rh-positive, 15% Rh-negative.
• Short notation for blood groups: e.g., AB+ or AB-.
• The image shows a model of blood group AB with (left) and without (right) the Rhesus antigen.

Role of Rhesus Factor in Pregnancy

• During pregnancy, Rh incompatibility can occur between a Rh-negative mother and an Rh-positive fetus.
• If the first child is Rh-positive and the mother is Rh-negative, during childbirth, the mother may be exposed to the fetal Rh antigen.
• This exposure can lead to the mother developing antibodies against the Rh antigen D.
• These antibodies can cross the placenta in subsequent pregnancies and attack Rh-positive fetal red blood cells.
• Antibody development requires initial exposure to the antigen, so the first contact usually isn't problematic, the second contact can lead to a life-threatening reaction.
• To prevent antibody formation after delivery, the mother is injected with anti-Rh antibodies immediately after the birth of an Rh-positive baby.
• These injected antibodies bind to and neutralize any fetal red blood cells that have entered the maternal circulation, preventing the mother's immune system from developing its own antibodies.
• There are over 30 different blood group systems with more than 600 known characteristics.

Overview of Inheritance Patterns

• This provides an overview of different modes of inheritance and associated diseases.

Autosomal Dominant

• Trait appears in almost every generation.
• If a child has the trait, at least one parent must also have it.
• Similar frequency in males and females.
• Examples: polydactyly, Huntington's disease, Marfan syndrome.

Autosomal Recessive

• Trait may skip generations.
• Children unaffected parents can be affected.
• Similar frequency in males and females.
• Examples: phenylketonuria, cystic fibrosis, sickle cell anemia.

X-Chromosomal Dominant

• All sons of an affected father are healthy
• All daughters of an affected father are affected.
• Females are generally more frequently affected.
• Examples: vitamin D-resistant rickets (very rare); other diseases in males often lethal.

X-Chromosomal Recessive

• Predominantly males are affected
• Females are only affected if the father is affected and the mother is a carrier.
• Examples: hemophilia, red-green color blindness, Duchenne muscular dystrophy.

Pedigree Analysis Exercises

• Practice problems of pedigrees with different inheritance patterns.
• Includes pedigrees for Huntington's disease and cystic fibrosis.
• Genetic analysis of pedigrees for determining inheritance patterns and genotypes of individuals.
• Understanding autosomal dominant, autosomal recessive, and X-linked recessive inheritance.

Blood Groups and Transfusions

• In 1901, Karl Landsteiner discovered blood groups A, B, and 0 through agglutination experiments with blood and serum.
• Later, the blood group AB was discovered, and Landsteiner received the Nobel Prize in 1930.

Agglutination Explanation

• Agglutination occurs due to the immune system.
• Red blood cells have antigens on the surface.
• The blood plasma contains antibodies.

Blood Group Antigens and Antibodies

• Blood group A: has A antigens and anti-B antibodies.
• Blood group B: has B antigens and anti-A antibodies.
• Blood group AB: has A and B antigens and no antibodies.
• Blood group 0: has no antigens and anti-A and anti-B antibodies.
• Frequencies of blood groups in Germany: 43% A, 11% B, 5% AB, and 41% 0.

Transfusion Compatibility

• Compatibility depends on the antigens on the donor red blood cells and the antibodies in the recipient's blood plasma.
• Shows a grid for which blood types can be transfused safely

Case Study of Charlie Chaplin

• Examines blood group inheritance for paternity tests.
• Since blood group inheritance follows Mendelian rules, it can be used to make statements concerning paternity within certain limits
• Pictured is the famous case of Charlie Chaplin, who was brought to court by Joan Barry after an affair

Single-Trait Experiment

• Varieties differed in only 1 trait (monohybrid)
• Mendel's Pioneer Achievements
• Statistical evaluation of thousands of samples for 12 years
• Research object: seed Pea (Pisum sativum)

Mendel's Results and His Rules - Dominant and recessive

• Combines two homozygous individuals one trait
• Crosses 2 heterozygote

Independent assortment

• Different traits are inherited independently of each other.
• The prerequisites for the Traits lie on different chromosomes

Breeding Scheme

• Combinatorial breeding is when, in crosses of livestock, the letters for the alleles can be written down in squares, along with the colored pigment and which color mark the animal has.
• Crossbreeding allows for new breeds of cattle

Dominant-Recessive Inheritance

• Crossbreeding diagram for the garden pea
• How could Mendel find out if the plants of the F2-Generation are homozygous or heterozygous
• By crossing the trait carriers with the recessive parent