Answered: mice, the A allele causes agouti fur,…

Human Anatomy & Physiology (11th Edition)

11th Edition

ISBN:9780134580999

Author:Elaine N. Marieb, Katja N. Hoehn

Publisher:Elaine N. Marieb, Katja N. Hoehn

Chapter1: The Human Body: An Orientation

Section: Chapter Questions

Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...

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Question

In mice, the A allele causes agouti fur, the A^Y allele causes yellow fur and is dominant to the A allele. The homozygous A^Y A^Y genotype is lethal. Why is the A^YA^Y homozygous condition lethal?

The A^Y allele lacks an upstream merc gene which is required for normal embryonic development.

The A^Y allele contains a null mutation in the A gene, which is required for normal embryonic development.

The yellow pigment produced by A allele is required for survival.

The A^Y allele highly transcribes the merc gene which is lethal in a homozygous A^YA^Y individual.

None of the other answers are correct.

Expert Solution

Step 1

The gene in question is thought to be important, and the deadly allele can be dominant or recessive.
Achondroplasia, a genetic disease that causes dwarfism, is an example of deadly alleles in humans.
When present in the homozygous state, the deadly allele is dominant and causes the organism's death (AA)
Heterozygotes will have a reduced stature (dwarfism), whereas homozygous recessive people will be normal size.
Lethal alleles modify genotypic and phenotypic ratios to the norm by triggering the death of one genotypic variety.
In most cases, a cross of two heterozygotes results in a 3:1 ratio (dominant: recessive)
Two dwarf heterozygotes are usually stated to be defined as the expected to produce a 2: 1 ratio in achondroplasia (the homozygous dominant does not survive).