WEEK 2 Flashcards
What happens during incomplete/partial dominance?
A cross between parents with contrasting traits may sometimes generate offspring with an intermediate phenotype
e.g a red and white flower will have offspring of pink flowers unlike Mendelian crosses where offspring can only be red or white
What occurs in Tay-Sachs disease?
Homozygous recessive individuals are severely affected with a fatal lipid-storage disorder and neonates die within their first three years. There is almost no activity of hexosaminidase A, an enzyme involved in lipid metabolism.
What is Tay-Sachs disease an example of?
Incomplete dominance
What is the threshold effect and in which disease can this be illustrated by?
The threshold effect is when normal phenotypic expression occurs anytime a minimal level of gene product is attained
What are the symptoms of Tay-Sachs disease?
- Progressive neurodegeneration
- Development delay
- Hyperreflexia (overreactive/overresponsive bodily reflexes)
- Hyperacusis (sensitive to a range of sounds)
- Lysosomes with onion skin
- hepatosplenomegaly (swollen liver and spleen)
What is codominance?
When both alleles contribute to the phenotype of the heterozygote
Multiple alleles can be studied only in ______________
Populations
Why can multiple alleles only be studied in populations?
Any individual diploid organism has at most only two homologous chromosomes therefore multiple alleles can only be studied among populations where numerous alternative forms of the same genes can exist
What is the history of the founding of ABO blood groups?
Discovered by Karl Landsteiner in the early 1900s
The ABO system is characterised by the presence of ________ on the surface of _________
- Antigens
- Red blood cells
Which chromosome is the gene that determines ABO blood group located?
Chromosome 9
Which mode of inheritance does the ABO system exhibit?
Codominance
How is the ABO phenotype tested in an individual?
A blood sample is mixed with an antiserum containing type A or type B antibodies. If an antigen is present on the surface of the person’s blood cells it will react with the antibody and cause agglutination of the red blood cells.
What are two practical applications of knowledge of human blood types?
Blood transfusions & organ transplants
The A and B antigens of blood are ______________
Carbohydrate groups
The specificity of the A and B antigens is based on the ________________ of the carbohydrate g
Terminal Sugar
Which three sugar molecules are in H substance?
Galactose (Gal)
N-acetylglucosamine (AgGluNH)
Fucose
What is the IA allele responsible for?
An enzyme that can add ten sugar N-acetylgalactosamine to the H substance
What is the H substance?
Something that all individuals have in which one or two terminal sugars are added
What is the IB allele responsible for?
A modified enzyme that cannot add N-acetylgalactosamine but instead can add a terminal galactose
What does being a carrier for Tay-sachs disease entail?
Being a carrier for tay-sachs disease will appear in the genotype but not the phenotype thus the individual will not have the symptoms of the disease
What is the correlation between blood groups and “H substance”?
All individuals will have “H substance” and antigens are added which differentiates to produce different blood groups
(those in blood group O will only have the H substance)
What do Heterozygotes (IAIB) do?
They add either one or the other sugar at the many sites available on the surface of the red blood cells, this illustrates the codominance of the AB blood type
Individuals of ______________ cannot add either terminal sugar; these persons have only the H substance on the surface of their red blood cells
Type O
FUT1 Gene produces an enzyme that makes ________
Fucose
What is the equation to make H substance?
H substance precursor + Fucose = H substance
Describe the “Bombay Phenotype”
Genetically the patient was type B but functionally type O. FUT1 gene had mutated which prevented fucose from attaching to the H substance which prevented the IA and IB alleles from recognising the incomplete H substance as a proper substrate. Neither antigen could be added to the cell surface therefore functionally she became type O.
