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Explain why there is a non-Mendelian 2:1 yellow/agouti phenotypic ratio in this cross.  b. What is the Raly gene? What does it encode? How does it relate to the lethality of Ay? c. 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 Pu

Explain why there is a non-Mendelian 2:1 yellow/agouti phenotypic ratio in this cross.  b. What is the Raly gene? What does it encode? How does it relate to the lethality of Ay? c. 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 Pu

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

b. What is the Raly gene? What does it encode? How does it relate to the lethality of Ay?

c. 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.

 

The Yellow Agouti Conundrum: Mendelian Genetics Meets Molecular Genetics Yellow mouse Agouti mouse (AA; also represented as A'/A") (AA"; also represented as A/A) Agouti is the common name for some animals of the genus Dasiprocta. 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 Dosiprocta. 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 (9 ) with a yellow buck ( ), their litter will be comprised of 2/3 yellow pups, 1/3 agouti (see genotypes above; A' 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 % to %). You will find in the formal scientific literature that A' (yellow) is a recessive lethal allele: a homozygous A'A" 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 (A'/A") is associated with the disruption of an RNA-binding protein. You may obtain more information in Silvers WK (1979) The Coat Colors of Mice, Springer Verlag, Chapter 2 (posted on Canvas). Remember to cite bibliographic or Internet sources if you happen to use additional references. You may not need this information, but it is here to give you an idea of the complexity of the alleles A/a, and its relationship with obesity. According to Hollander WF and Gowen JW (1956) J Hered 47:221-224, other fur color alleles at the agouti locus and their phenotypes in the mouse (Mus musculus) are: a "black," non-agouti, yellow hair in the ears and around the perineum a* extreme non-agouti a' "black-and-tan" (belly yellowish, rest of the body black) A wild type (uniformly agouti) A" "white-bellied," or yellow-bellied agouti A "yellow," lethal if homozygous; the heterozygote is obese
Transcribed Image Text:The Yellow Agouti Conundrum: Mendelian Genetics Meets Molecular Genetics Yellow mouse Agouti mouse (AA; also represented as A'/A") (AA"; also represented as A/A) Agouti is the common name for some animals of the genus Dasiprocta. 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 Dosiprocta. 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 (9 ) with a yellow buck ( ), their litter will be comprised of 2/3 yellow pups, 1/3 agouti (see genotypes above; A' 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 % to %). You will find in the formal scientific literature that A' (yellow) is a recessive lethal allele: a homozygous A'A" 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 (A'/A") is associated with the disruption of an RNA-binding protein. You may obtain more information in Silvers WK (1979) The Coat Colors of Mice, Springer Verlag, Chapter 2 (posted on Canvas). Remember to cite bibliographic or Internet sources if you happen to use additional references. You may not need this information, but it is here to give you an idea of the complexity of the alleles A/a, and its relationship with obesity. According to Hollander WF and Gowen JW (1956) J Hered 47:221-224, other fur color alleles at the agouti locus and their phenotypes in the mouse (Mus musculus) are: a "black," non-agouti, yellow hair in the ears and around the perineum a* extreme non-agouti a' "black-and-tan" (belly yellowish, rest of the body black) A wild type (uniformly agouti) A" "white-bellied," or yellow-bellied agouti A "yellow," lethal if homozygous; the heterozygote is obese
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