Assume that a particular genetic condition in a mammalian species causes an inability to digest starch. this disorder occurs with equal frequency in males and females. In most cases, neither parent of the affected offspring has the condition.
(a) Describe the most probable pattern of inheritance for this condition. Explain your reasoning. Include in your disscusion a sample cross(es) sufficient to verify your proposed pattern.
(b) Explain how mutation could cause this inability to digest starch.
(c) Describe how modern techniques od molecular biology could be used to determine whether the mutant allele is present in a given individual.
biology
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(a) The most probable pattern of inheritance for this condition is autosomal recessive.
Reasoning: Equal frequency in males and females suggests that the gene responsible for this condition is not located on the sex chromosomes (X or Y). Since neither parent of the affected offspring has the condition, it indicates that they are carriers of the mutated gene. This suggests that the disorder is likely inherited in an autosomal recessive manner, as carriers (heterozygous individuals) do not exhibit the disorder.
To verify this pattern, a cross between two carriers (parents) can be performed. Let's designate the normal allele as "A" and the mutant allele as "a".
Possible parental genotypes:
Parent 1: Aa (carrier)
Parent 2: Aa (carrier)
Sample cross:
A a
------------------
A | AA Aa
a | Aa aa
In this cross, the Punnett square shows that there is a 25% chance (1 out of 4) of producing an affected offspring (aa genotype).
(b) The inability to digest starch can be caused by a mutation in a gene that encodes an enzyme involved in starch digestion, such as amylase. Amylase is responsible for breaking down starch into smaller glucose molecules that can be absorbed by the body. A mutation in the gene encoding amylase can lead to the production of a non-functional or less efficient enzyme, resulting in the inability to digest starch properly.
(c) Modern techniques of molecular biology could be used to determine the presence of the mutant allele in a given individual. Here is a step-by-step description of how this could be done:
1. DNA Extraction: Obtain a tissue sample (e.g., blood or cheek swab) from the individual.
2. PCR (Polymerase Chain Reaction): Use a technique called PCR to amplify the specific region of the gene of interest that contains the mutant allele. PCR involves using DNA primers that flank the target region to selectively amplify only the specific DNA fragment.
3. Gel Electrophoresis: Separate the PCR-amplified DNA fragments in a gel matrix based on their size using gel electrophoresis. This technique allows the visualization of the DNA fragments and distinction between the normal and mutant alleles based on their size differences.
4. DNA Sequencing: If necessary, perform DNA sequencing to determine the exact nucleotide sequence of the amplified fragments. This helps identify specific mutations within the gene that may be responsible for the inability to digest starch.
By comparing the DNA sequence with known normal and mutant sequences, molecular biologists can confirm whether an individual has the mutant allele associated with the inability to digest starch.
(a) Based on the information provided, the most probable pattern of inheritance for this condition is autosomal recessive inheritance. This pattern suggests that the condition is caused by a recessive allele on an autosome (a non-sex chromosome) and requires two copies of the mutant allele for the trait to be expressed.
To verify this pattern, we can perform a test cross. A test cross involves crossing an individual with the unknown genotype (in this case, an affected individual) with a homozygous recessive individual (one that is known to carry two copies of the normal allele). If the trait is inherited as an autosomal recessive condition, we would expect the offspring to have a 1:1 ratio of affected to unaffected individuals.
For example, let's assume that the unknown genotype for the affected individual is represented by Aa (where A represents the normal allele and a represents the mutant allele). A test cross would involve crossing the affected individual (Aa) with an individual who is homozygous recessive for the condition (aa). The resulting offspring would have the following genotypes: Aa (affected) and aa (unaffected). This would support the pattern of autosomal recessive inheritance.
(b) Mutation could cause the inability to digest starch by altering the structure or function of a gene involved in starch digestion. Starch digestion relies on several enzymes produced by specific genes. A mutation in one of these genes could result in a non-functional or less efficient enzyme, leading to the inability to digest starch.
For instance, a mutation might disrupt the gene responsible for producing the enzyme amylase, which breaks down starch into smaller molecules that can be absorbed and utilized by the body. If the mutant allele encodes a non-functional or less efficient amylase enzyme, individuals carrying two copies of this allele would have impaired starch digestion.
(c) Modern techniques of molecular biology could be used to determine whether the mutant allele is present in a given individual. One of the commonly used techniques is DNA sequencing. DNA sequencing allows us to read the genetic code of an individual and identify any variations or mutations in specific genes.
To determine the presence of the mutant allele, we would need to analyze the DNA of the given individual and specifically look for the presence of the mutant allele associated with the inability to digest starch. By comparing the sequence of the individual's gene of interest with a known normal reference sequence, we can identify any differences or mutations in the gene.
Additionally, other molecular techniques such as polymerase chain reaction (PCR) could be used to specifically amplify the region of interest before sequencing. This allows for more efficient and targeted analysis of the gene of interest.
Overall, molecular biology techniques provide a powerful tool to analyze the presence of specific genetic variants, including the mutant allele associated with the inability to digest starch.