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a. What is the Raly gene? What does it encode? How does it relate to the lethality of Ay? b.  A heterozygous mouse AAy does not produce enough pigment and it is yellow. Homozygous individuals die during development, but AAy heterozygous do not. Why? You may use any graphic aid to explain this, if necessary. This means that you may use a Punnett square or a forking segregation diagram, or computations with fractions. c. Explain why there is a non-Mendelian 2:1 yellow/agouti phenotypic ratio in this cross.

a. What is the Raly gene? What does it encode? How does it relate to the lethality of Ay? b.  A heterozygous mouse AAy does not produce enough pigment and it is yellow. Homozygous individuals die during development, but AAy heterozygous do not. Why? You may use any graphic aid to explain this, if necessary. This means that you may use a Punnett square or a forking segregation diagram, or computations with fractions. c. Explain why there is a non-Mendelian 2:1 yellow/agouti phenotypic ratio in this cross.

Human Anatomy & Physiology (11th Edition)
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
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a. What is the Raly gene? What does it encode? How does it relate to the lethality of Ay?

b.  A heterozygous mouse AAy does not produce enough pigment and it is yellow. Homozygous individuals die during development, but AAy heterozygous do not. Why? You may use any graphic aid to explain this, if necessary. This means that you may use a Punnett square or a forking segregation diagram, or computations with fractions.

c. Explain why there is a non-Mendelian 2:1 yellow/agouti phenotypic ratio in this cross. 

 

**The Yellow Agouti Conundrum: Mendelian Genetics Meets Molecular Genetics** **Images:** - Agouti Mouse (Genotype: AA; also represented as A¹A¹) - Yellow Mouse (Genotype: AʸAʸ; also represented as A¹Aʸ) **Text:** Agouti is the common name for some animals of the genus *Dasyprocta*. The term “agouti” is also used to describe the fur color of other mammals, such as the mouse (*Mus musculus*), if they show a banded fur color reminiscent of *Dasyprocta*. Very importantly, the agouti gene (a) may be associated with obesity. Overexpression of the murine agouti gene in cultured human adipocytes prevents degradation of fats. After mating two mice, i.e., a yellow doe (♀) with a yellow buck (♂), their litter will be comprised of 2/3 yellow pups, 1/3 agouti (see genotypes above; A¹ indicates the wild type allele). Since by now you are more familiar with transmission genetics, you notice that this phenotypic proportion is not right (i.e., it is not ¾ to ¼). You will find in the formal scientific literature that Aʸ (yellow) is a recessive lethal allele: a homozygous AʸAʸ does not develop after fertilization or perishes early in pre-natal development. Phenotypes are analyzed only in living offspring, hence recessive lethal alleles are considered when considering genotypes and discrepancies between the genotypic proportions vs. phenotypic proportions. This seemingly incongruous relation between lethality and fur color has been explained at the level of molecular genetics. See articles posted on Canvas; Michaud et al. (1993) Genes Dev 7:1203-1213 and Duhl et al. (1994) Development 120:1695-1708. Here’s an intriguing thing: The embryonic lethality of homozygous lethal yellow mice (AʸAʸ) is associated with the disruption of an RNA-binding protein. You may refer to the classic monograph by Searle's WK (1979) *The Coat Colors of Mice*, Springer Verlag, Chapter 2 (posted on Canvas) or seek articles in books or internet sources if you happen to use additional references. There are vestigial differences in how
Transcribed Image Text:**The Yellow Agouti Conundrum: Mendelian Genetics Meets Molecular Genetics** **Images:** - Agouti Mouse (Genotype: AA; also represented as A¹A¹) - Yellow Mouse (Genotype: AʸAʸ; also represented as A¹Aʸ) **Text:** Agouti is the common name for some animals of the genus *Dasyprocta*. The term “agouti” is also used to describe the fur color of other mammals, such as the mouse (*Mus musculus*), if they show a banded fur color reminiscent of *Dasyprocta*. Very importantly, the agouti gene (a) may be associated with obesity. Overexpression of the murine agouti gene in cultured human adipocytes prevents degradation of fats. After mating two mice, i.e., a yellow doe (♀) with a yellow buck (♂), their litter will be comprised of 2/3 yellow pups, 1/3 agouti (see genotypes above; A¹ indicates the wild type allele). Since by now you are more familiar with transmission genetics, you notice that this phenotypic proportion is not right (i.e., it is not ¾ to ¼). You will find in the formal scientific literature that Aʸ (yellow) is a recessive lethal allele: a homozygous AʸAʸ does not develop after fertilization or perishes early in pre-natal development. Phenotypes are analyzed only in living offspring, hence recessive lethal alleles are considered when considering genotypes and discrepancies between the genotypic proportions vs. phenotypic proportions. This seemingly incongruous relation between lethality and fur color has been explained at the level of molecular genetics. See articles posted on Canvas; Michaud et al. (1993) Genes Dev 7:1203-1213 and Duhl et al. (1994) Development 120:1695-1708. Here’s an intriguing thing: The embryonic lethality of homozygous lethal yellow mice (AʸAʸ) is associated with the disruption of an RNA-binding protein. You may refer to the classic monograph by Searle's WK (1979) *The Coat Colors of Mice*, Springer Verlag, Chapter 2 (posted on Canvas) or seek articles in books or internet sources if you happen to use additional references. There are vestigial differences in how
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