Problem 10 - Biology Concepts and Applications

Question

Your sister gives you a purebred Labrador retriever, a female named Dandelion. Suppose you decide to breed Dandelion and sell puppies to help pay for your college tuition. Then you discover that two of her four brothers and sisters show hip dysplasia, a heritable disorder arising from a number of gene interactions. If Dandelion mates with a male Labrador known to be free of the harmful alleles, can you guarantee to a buyer that her puppies will not develop the disorder? Explain your answer.

Step-by-Step Solution

Answer

No, you can't guarantee they won't carry the gene, but puppies won't express it due to the male's healthy alleles.

Step 1: Understand Genetic Heredity

Hip dysplasia is a genetic disorder that can be passed from parents to offspring. If a Labrador exhibits hip dysplasia, it has alleles that cause the condition. Since Dandelion's siblings show the disorder, it's possible that she carries the harmful alleles as well.

Step 2: Analyze Dandelion's Genotype

Dandelion's siblings have hip dysplasia, which suggests the disorder could be recessive. This means Dandelion could be a carrier (heterozygous) or, less likely, also express the disorder (homozygous recessive). Her genotype is therefore uncertain based solely on her siblings' conditions.

Step 3: Consider Male Labrador's Genotype

The male Labrador is known to be free of harmful alleles for hip dysplasia, indicating he is homozygous dominant (does not carry or express the disorder). Any alleles contributed by him to the offspring will not include the disorder-causing genes.

Step 4: Apply Genetic Probability

Since the male contributes non-harmful alleles and assuming Dandelion is a carrier, each puppy will have at least one non-disorder allele from their father. However, if Dandelion carries a recessive harmful allele, each puppy has a 50% chance of being a carrier but will not express the disorder.

Step 5: Conclusion on Puppy Health

You cannot guarantee that none of the puppies will carry a harmful allele, but they will not express the disorder because they will receive at least one healthy allele from their father. Breeding with a non-carrier ensures puppies will not develop hip dysplasia.

Key Concepts

Hip Dysplasia

Hip dysplasia is a common genetic disorder in dogs, particularly in large breeds like Labrador Retrievers. It affects the hip joints of the animals, leading to discomfort and mobility issues as they age. The condition arises from the improper development of the hip socket, and is influenced by both genetic and environmental factors. If a dog has hip dysplasia, it may experience joint pain or arthritis, and in severe cases, may require surgical intervention.

When breeding dogs, understanding the genetic implications of hip dysplasia is essential. This disorder is heritable, meaning it can be passed down from affected parents to their offspring. Responsible breeding practices focus on reducing the prevalence of such genetic disorders by careful selection and monitoring of breeding pairs.

Genotype Analysis

Genotype analysis is a critical component in predicting whether an animal might pass certain genetic traits to its offspring. In the case of Dandelion, analyzing her genotype can help determine the likelihood of her puppies developing or carrying hip dysplasia.

This analysis involves understanding whether Dandelion’s genetic makeup contains alleles (different forms of a gene) associated with hip dysplasia. Since her siblings exhibit the disorder, she may carry the recessive alleles that contribute to it. In practical terms, determining the exact genotype would require genetic testing, which can identify the specific combinations of alleles Dandelion holds.

Recessive Alleles

Genetic inheritance often involves dominant and recessive alleles. For a disorder like hip dysplasia, which may be recessive, the puppy must inherit two copies of the harmful allele (one from each parent) to express the disorder.

If Dandelion has the genetic makeup heterozygous for the gene responsible for hip dysplasia, she would carry one normal allele and one recessive allele. Even though she does not exhibit symptoms, she can still pass on the recessive allele to her puppies. Only when paired with another recessive allele from the other parent would the disorder manifest.

• Labs that are homozygous dominant (two healthy alleles) are unaffected and do not carry the disorder.
• Carrier labs are heterozygous and can pass on the disorder without showing symptoms.

Carrier Genetics

In genetic terms, a carrier is an individual that has one copy of a recessive allele for a particular trait or disorder, and the trait is not expressed in the phenotype. Dandelion's genotype suggests that she might be a carrier for the alleles causing hip dysplasia.

Being a carrier means that while Dandelion does not exhibit hip dysplasia, she can pass the recessive allele to her offspring. If her puppies inherit a recessive allele from Dandelion and a normal allele from a homozygous dominant parent, they will be carriers. However, if bred with a Labrador that is not a carrier, the disorders's expression in the offspring can be prevented.

• The offspring inherit healthy alleles from the father ensuring the disorder is not expressed.
• Though not expressed, the puppies can still be carriers, as they may inherit Dandelion's recessive allele.

Responsible breeding practices seek to control these traits, reducing the incidence of genetic disorders in future generations.