It’s a very well-known fact that most dragons do not breathe fire, and it’s also
ID: 64873 • Letter: I
Question
It’s a very well-known fact that most dragons do not breathe fire, and it’s also well known that alleles that enable fire breathing are recessive to the wild-type Sweet Breath phenotype. However, it’s unclear how many different genes, when mutated, cause the fire breathing phenotype. To answer this question you use four different strains of dragon and perform a series of crosses. Your strains are the Hungarian Horntail (Strain A), the Norwegian Ridgeback (Strain B), the Romanian Longhorn (Strain C), and the Swedish Shortsnout (Strain D). All strains are true breeding for a single homozygous recessive mutation that allows them to breathe fire. Cross #1 Hungarian Horntail (A) X Norwegian Ridgeback (B) = F1: All Sweet Breath Cross #2 Romanian Longhorn (C) X Swedish Shortsnout (D) = F1: All Sweet Breath Cross #3 Swedish Shortsnout (D) X Norwegian Ridgeback (B) = F1: All Firebreathing Cross #4 Romanian Longhorn (C) X Hungarian Horntail (A) = F1: All Firebreathing How many genes are involved in creating a firebreathing phenotype?
Explanation / Answer
AA (Hungarian Horntail) X BB (Norwegian Ridgeback)
F1 generation
A
A
B
AB
AB
B
AB
AB
The cross between the two homozygous recessive dragons has ended up developing all sweet breath dragons.
CC (Romanian Longhorn) X DD (Swedish Shortsnout)
F1 generation
C
C
D
CD
CD
D
CD
CD
The cross between the two homozygous recessive dragons has ended up developing all sweet breath dragons.
DD (Swedish Shortsnout) X BB (Norwegian Ridgeback)
F1 generation
D
D
B
DB
DB
B
DB
DB
CC (Romanian Longhorn) X AA (Hungarian Horntail)
F1 generation
C
C
A
CA
CA
A
CA
CA
The last two crosses has produced an all fire breathing dragons in its F1 generation.
In the penultimate cross between the swedish Shortsnout (D) and Norwegian Ridgeback (B), it should be noted that a mutation in any one of the gene is mutated, it makes the other gene recessive and expressive itself in the absence of the wild-type gene (sweet breath).
The same is the case between the cross between a Romanian Longhorn (C) and the Hungarian Horntain (A), where the mutation in any one of the genes would lead to the formation of a fire breath dragons instead of the sweet breath dragons.
A
A
B
AB
AB
B
AB
AB
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