WEEK 2

Question 1

What happens during incomplete/partial dominance?

Answer 1

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

Question 2

What occurs in Tay-Sachs disease?

Answer 2

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.

Question 3

What is Tay-Sachs disease an example of?

Answer 3

Incomplete dominance

Question 4

What is the threshold effect and in which disease can this be illustrated by?

Answer 4

The threshold effect is when normal phenotypic expression occurs anytime a minimal level of gene product is attained

Question 5

What are the symptoms of Tay-Sachs disease?

Answer 5

• 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)

Question 6

What is codominance?

Answer 6

When both alleles contribute to the phenotype of the heterozygote

Question 7

Multiple alleles can be studied only in ______________

Answer 7

Populations

Question 8

Why can multiple alleles only be studied in populations?

Answer 8

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

Question 9

What is the history of the founding of ABO blood groups?

Answer 9

Discovered by Karl Landsteiner in the early 1900s

Question 10

The ABO system is characterised by the presence of ________ on the surface of _________

Answer 10

1. Antigens
2. Red blood cells

Question 11

Which chromosome is the gene that determines ABO blood group located?

Answer 11

Chromosome 9

Question 12

Which mode of inheritance does the ABO system exhibit?

Answer 12

Codominance

Question 13

How is the ABO phenotype tested in an individual?

Answer 13

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.

Question 14

What are two practical applications of knowledge of human blood types?

Answer 14

Blood transfusions & organ transplants

Question 15

The A and B antigens of blood are ______________

Answer 15

Carbohydrate groups

Question 16

The specificity of the A and B antigens is based on the ________________ of the carbohydrate g

Answer 16

Terminal Sugar

Question 17

Which three sugar molecules are in H substance?

Answer 17

Galactose (Gal)
N-acetylglucosamine (AgGluNH)
Fucose

Question 18

What is the IA allele responsible for?

Answer 18

An enzyme that can add ten sugar N-acetylgalactosamine to the H substance

Question 19

What is the H substance?

Answer 19

Something that all individuals have in which one or two terminal sugars are added

Question 20

What is the IB allele responsible for?

Answer 20

A modified enzyme that cannot add N-acetylgalactosamine but instead can add a terminal galactose

Question 21

What does being a carrier for Tay-sachs disease entail?

Answer 21

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

Question 22

What is the correlation between blood groups and “H substance”?

Answer 22

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)

Question 23

What do Heterozygotes (IAIB) do?

Answer 23

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

Question 24

Individuals of ______________ cannot add either terminal sugar; these persons have only the H substance on the surface of their red blood cells

Answer 24

Type O

Question 25

FUT1 Gene produces an enzyme that makes ________

Answer 25

Fucose

Question 26

What is the equation to make H substance?

Answer 26

H substance precursor + Fucose = H substance

Question 27

Describe the “Bombay Phenotype”

Answer 27

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.