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Chapter 5: Problem 14

The \(L^{\mathrm{M}}\) and \(L^{\mathrm{N}}\) alleles at the MN blood-group locus exhibit codominance. Give the expected genotypes and phenotypes and their ratios in progeny resulting from the following crosses. a. \(L^{\mathrm{M}} L^{\mathrm{M}} \times L^{\mathrm{M}} L^{\mathrm{N}}\) b. \(L^{\mathrm{N}} L^{\mathrm{N}} \times L^{\mathrm{N}} L^{\mathrm{N}}\) c. \(L^{\mathrm{M}} L^{\mathrm{N}} \times L^{\mathrm{M}} L^{\mathrm{N}}\) d. \(L^{\mathrm{M}} L^{\mathrm{N}} \times L^{\mathrm{N}} L^{\mathrm{N}}\) e. \(L^{\mathrm{M}} L^{\mathrm{M}} \times L^{\mathrm{N}} L^{\mathrm{N}}\)

Short Answer

Expert verified
a. 1:1 M:MN; b. all N; c. 1:2:1 M:MN:N; d. 1:1 MN:N; e. all MN.

Step by step solution

01

Understanding Codominance

In codominance, both alleles contribute equally to the phenotype. In this case, both the \(L^{\mathrm{M}}\) and \(L^{\mathrm{N}}\) alleles express themselves when present together, resulting in a phenotype that displays both traits, MN.
02

Analyzing Cross (a)

For the cross \(L^{\mathrm{M}} L^{\mathrm{M}} \) and \(L^{\mathrm{M}} L^{\mathrm{N}}\), the possible genotypes are \(L^{\mathrm{M}} L^{\mathrm{M}}\) and \(L^{\mathrm{M}} L^{\mathrm{N}}\). These result in a phenotypic ratio of 1:1, with offspring expressing either M or MN phenotypes.
03

Analyzing Cross (b)

For the cross \(L^{\mathrm{N}} L^{\mathrm{N}}\) and \(L^{\mathrm{N}} L^{\mathrm{N}}\), all offspring have the genotype \(L^{\mathrm{N}} L^{\mathrm{N}}\), resulting in a phenotype of N in a 1:0 ratio.
04

Analyzing Cross (c)

In the cross \(L^{\mathrm{M}} L^{\mathrm{N}}\) and \(L^{\mathrm{M}} L^{\mathrm{N}}\), the possible genotypes are \(L^{\mathrm{M}} L^{\mathrm{M}}\), \(L^{\mathrm{M}} L^{\mathrm{N}}\), and \(L^{\mathrm{N}} L^{\mathrm{N}}\), with a phenotypic ratio of 1:2:1 for M, MN, and N respectively.
05

Analyzing Cross (d)

For \(L^{\mathrm{M}} L^{\mathrm{N}}\) and \(L^{\mathrm{N}} L^{\mathrm{N}}\), the genotypes are \(L^{\mathrm{M}} L^{\mathrm{N}}\) and \(L^{\mathrm{N}} L^{\mathrm{N}}\) with a phenotypic ratio of 1:1, showing MN and N phenotypes.
06

Analyzing Cross (e)

In the cross \(L^{\mathrm{M}} L^{\mathrm{M}}\) and \(L^{\mathrm{N}} L^{\mathrm{N}}\), all offspring have the genotype \(L^{\mathrm{M}} L^{\mathrm{N}}\), resulting in an MN phenotype in the proportion of 1:0.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

MN blood group
The MN blood group is a great example to understand the concept of codominance. Blood groups are ways to categorize blood based on the presence or absence of certain antigens found on the surface of red blood cells. The MN blood group system involves two alleles:
  • \(L^{\mathrm{M}}\)
  • \(L^{\mathrm{N}}\)
When an individual inherits both \(L^{\mathrm{M}}\) and \(L^{\mathrm{N}}\) alleles, their blood type is neither purely M nor N. Instead, it is classified as MN. This is because both alleles express themselves equally and simultaneously. No allele overshadows the other, highlighting codominance.
Understanding the MN blood group allows us to see a real-world scenario of how genetic alleles can influence physical traits. It's an excellent tool for teaching how genes can work together or independently.
Phenotypic ratio
The phenotypic ratio is a way of expressing the different visible outcomes or phenotypes resulting from a genetic cross. When the alleles involved exhibit codominance, like in the MN blood group, understanding phenotypic ratios becomes more interesting. In the cross \(L^{\mathrm{M}} L^{\mathrm{M}}\) with \(L^{\mathrm{M}} L^{\mathrm{N}}\), we would see offspring in the following phenotypes:
  • 50% with M phenotype
  • 50% with MN phenotype
This results in a 1:1 phenotypic ratio.
Meanwhile, a cross between \(L^{\mathrm{N}} L^{\mathrm{N}}\) and \(L^{\mathrm{N}} L^{\mathrm{N}}\) results in offspring all displaying the N phenotype, leading to a 1:0 ratio.
Expressing outcomes in ratios helps geneticists predict trait inheritance patterns, especially in more complex systems involving codominance.
Genotype analysis
Genotype analysis involves examining the genetic constitution or genotype of an organism to predict possible phenotypes. With the MN blood group system, genotype involves the pairing of the two alleles, \(L^{\mathrm{M}}\) and \(L^{\mathrm{N}}\). This is crucial to determine the outcomes in crosses. Consider a cross of \(L^{\mathrm{M}} L^{\mathrm{N}}\) with \(L^{\mathrm{M}} L^{\mathrm{N}}\). The potential genotypes of offspring include:
  • \(L^{\mathrm{M}} L^{\mathrm{M}}\)
  • \(L^{\mathrm{M}} L^{\mathrm{N}}\)
  • \(L^{\mathrm{N}} L^{\mathrm{N}}\)
This offspring distribution results in a 1:2:1 phenotypic ratio, showcasing three possible outcomes: M, MN, and N.
Analyzing the genotype is essential to understand how traits are passed from one generation to another and how they manifest physically as phenotypes.

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Most popular questions from this chapter

In goats, a beard is produced by an autosomal allele that is dominant in males and recessive in females. We'll use the symbol \(B^{\mathrm{b}}\) for the beard allele and \(B^{+}\) for the beardless allele. Another independently assorting autosomal allele that produces a black coat \((W)\) is dominant to the allele for white coat \((w) .\) Give the phenotypes and their expected proportions for the following crosses. a. \(B^{+} B^{\mathrm{b}}\) Ww male \(\times B^{+} B^{\mathrm{b}}\) Ww female b. \(B^{+} B^{\mathrm{b}}\) Ww male \(\times B^{+} B^{\mathrm{b}}\) Ww female c. \(B^{+} B^{+}\) Ww male \(\times B^{\mathrm{b}} B^{\mathrm{b}}\) Ww female d. \(B^{+} B^{\mathrm{b}}\) Ww male \(\times B^{\mathrm{b}} B^{\mathrm{b}}\) Ww female

Turkeys have black, bronze, or black-bronze plumage. Examine the results of the following crosses: $$ \begin{array}{ll} {\text { Parents }} & {\text { Offspring }} \\ \hline \text { Cross 1: black and bronze } & \text { all black } \\ \text { Cross 2: black and black } & 3 / 4 \text { black, } 1 / 4 \text { bronze } \\ \text { Cross 3: black-bronze and } & \text { all black-bronze } \\ \text { black-bronze } & \\ \text { Cross 4: black and bronze } & 1 / 2 \text { black, } 1 / 4 \text { bronze, } 1 / 4 \\ & \text { black-bronze } \\ \text { Cross 5: bronze and black- } & 1 / 2 \text { bronze, } 1 / 2 \text { black-bronze } \\ \text { bronze } & \\ \text { Cross 6: bronze and bronze } &\\\ &\text {4 bronze,} \text {1 / 4 black-bronze} \end{array} $$ Do you think these differences in plumage arise from incomplete dominance between two alleles at a single locus? If yes, support your conclusion by assigning symbols to each allele and providing genotypes for all turkeys in the crosses. If your answer is no, provide an alternative explanation and assign genotypes to all turkeys in the crosses.

Suppose that you are tending a mouse colony at a genetic research institute, and one day you discover a mouse with twisted ears. You breed this mouse with twisted ears and find that the trait is inherited. Both male and female mice may have twisted ears, but when you cross a twisted-eared male with a normal- eared female, you obtain results that differ from those obtained when you cross a twisted-eared female with a normal-eared male: the reciprocal crosses give different results. Describe how you would determine whether this trait results from a sex-linked gene, a sex-influenced gene, genetic maternal effect, a cytoplasmically inherited gene, or genomic imprinting. What crosses would you conduct, and what results would be expected with these different types of inheritance?

What is gene interaction? What is the difference between an epistatic gene and a hypostatic gene?

Match each of the following terms with its correct definition (parts \(a\) through \(i\) ) Phenocopy __________ Pleiotropy __________ Polygenic trait ____________ Penetrance _________ Sex-limited trait _________ Genetic maternal effect __________ Genomic imprinting __________ Sex-influenced trait _________ Anticipation __________ a. The percentage of individuals with a particular genotype that express the expected phenotype. b. A trait determined by an autosomal gene that is more easily expressed in one sex. c. A trait determined by an autosomal gene that is expressed in only one sex. d. A trait that is determined by an environmental effect and that has the same phenotype as a genetically determined trait. e. A trait determined by genes at many loci. f. The expression of a trait is affected by the sex of the parent that transmits the gene to the offspring. g. The trait appears earlier or is more severe in succeeding generations. h. A gene affects more than one phenotype. i. The genotype of the maternal parent influences the phenotype of the offspring.
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