Question

The following genotypes of two independently assorting autosomal genes determine coat color in rats: \(A-B-(\text { gray }) ; A-b b\) (yellow) \(; a a B-\) (black); \(a a b b\) (cream) A third gene pair on a separate autosome determines whether any color will be produced. The \(C C\) and \(C c\) genotypes allow color according to the expression of the \(A\) and \(B\) alleles. However, the ce genotype results in allbino rats regardless of the \(A\) and \(B\) alleles present. Determine the \(F_{1}\) phenotypic ratio of the following crosses: (a)AAbbCC \(\times\) aaBBcc; (b) \(A a B B c c \times A A B b c c\) (c) \(A a B b C c \times A a B b c c\)

Short answer

What is the F1 phenotypic ratio for the following crosses for a three-gene system determining coat color in rats: (a) AAbbCC x aaBBcc: 100% gray (b) AaBBcc x AABBcc: 100% albino (c) AaBbCc x AaBbcc: 3:3:1:1:4 (gray:black:yellow:cream:albino)

Step-by-step solution

Analyze the given genotypes

Start by writing down the parent genotypes: AAbbCC and aaBBcc. Note that gene A is heterozygous in one parent and homozygous recessive in the other parent, gene B is homozygous in both parents but with different alleles, and gene C is homozygous in both parents but with different alleles.

Determine the genotype probabilities for the offspring

Using the rules of probability, determine the offspring's genotype probabilities for each gene: - For gene A: (Aa) - For gene B: (AB or Ba) - For gene C: (Cc)

Combine the probability to determine the F1 phenotypes

The combined genotype of the offspring will be AaBbCc. According to the provided information on the genotype and phenotype relationship, this genotype will result in gray coat color because the dominant alleles A and B are both present and the genotype Cc allows color according to the gene A and B alleles being present. Therefore, the \(F_{1}\) phenotypic ratio for this cross is 100% gray. ##Cross (b): AaBBcc \(\times\) AABBcc##

Analyze the given genotypes

Start by writing down the parent genotypes: AaBBcc and AABBcc. Note that gene A is heterozygous in one parent and homozygous dominant in the other parent, gene B is homozygous dominant for both parents, and gene C is homozygous recessive for both parents.

Determine the genotype probabilities for the offspring

Using the rules of probability, determine the offspring's genotype probabilities for each gene: - For gene A: (AA or Aa) - For gene B: (BB) - For gene C: (cc)

Combine the probability to determine the F1 phenotypes

The possible genotypes of the offspring are AABBcc and AaBBcc. However, since the genotype cc is homozygous recessive for gene C, it results in albino rats regardless of the A and B alleles present. Therefore, the \(F_{1}\) phenotypic ratio for this cross is 100% albino. ##Cross (c): AaBbCc \(\times\) AaBbcc##

Analyze the given genotypes

Start by writing down the parent genotypes: AaBbCc and AaBbcc. Note that gene A is heterozygous in both parents, gene B is heterozygous in one parent and homozygous recessive in the other parent, and gene C is heterozygous in one parent and homozygous recessive in the other parent.

Determine the genotype probabilities for the offspring

Using the rules of probability, determine the offspring's genotype probabilities for each gene: - For gene A: (AA, Aa, aA, or aa) - For gene B: (BB, Bb, bB, or bb) - For gene C: (CC, Cc, or cc)

Combine the probability to determine the F1 phenotypes

There are multiple possible genotypes for the offspring, so the phenotypic outcome will vary based on the final combination. However, knowing the relationship between the genotypes and phenotypes, we can do a weighted calculation by the number of each phenotype: - 3 gray:[\((AA,B_,C_)\), \((Aa,B_,C_)\) or \((Aa,B_,Cc)\)] - 3 black:[\((aa,B_,C_)\), \((aa,B_,C_)\) or \((aA,B_,Cc)\)] - 1 yellow:[\((A_,bb,C_)\)] - 1 cream:[\((a a b b C_)\)] - 4 albino:[\((_,_,cc)\)] Therefore, the \(F_{1}\) phenotypic ratio for this cross is \(3:3:1:1:4\) (gray:black:yellow:cream:albino).

Key concepts

Autosomal Genes

In genetics, autosomal genes refer to genes located on non-sex chromosomes, also known as autosomes. Humans, for example, have 22 pairs of autosomes. Genes on these chromosomes typically follow Mendelian inheritance patterns. This means that alleles, which are different forms of a gene, segregate and independently assort during the formation of gametes. For instance, if we're looking at genes determining coat color in rats, these are autosomal genes because they are found on the non-sex chromosomes.
Such genes can interact independently to influence phenotypic traits, such as color. For example, the gene combinations for coat color in certain rat models might include alleles that are dominant or recessive, affecting the resulting phenotype of their offspring based on Mendelian inheritance laws.

Phenotypic Ratio

Phenotypic ratio is an outcome from genetic crosses which expresses the relative number of different phenotypes appearing in the offspring. When predicting coat colors in rats, understanding phenotypic ratios is crucial.
By calculating potential combinations between alleles of two genes (say A and B), you can determine the visible traits (phenotypes) and express this as a ratio. For example, if a cross results in offspring with a variety of coat colors, you might calculate a phenotypic ratio of 3:1 or 9:3:3:1, depending on the interactions of multiple genes.
This ratio directly influences predictions on how traits will manifest in a population, giving essential insight into the genetic structure of offspring.

Genotype Probabilities

Genotype probabilities help us predict the likelihood of certain genetic makeups in the offspring. This involves understanding dominant and recessive alleles, especially in autosomal genes such as those determining coat color.
Each parent can pass on one allele from each gene pair, influencing the genotype of the offspring. For instance, if a rat has genotypes like AaBbCc, you can calculate probabilities for possible offspring genotypes like Aa, BB, or cc based on Mendelian genetics.

• A 50% probability for dominant alleles gives Aa.
• A 25% probability might result in recessive aa.
• Such calculations help predict the distribution of traits in a mating population.

Understanding these probabilities is vital for predicting phenotypic outcomes.

Coat Color Inheritance

Coat color inheritance in animals, such as rats, is a well-studied genetic trait often used to illustrate basic genetic principles. This trait is influenced by multiple genes, each with different alleles that can be dominant or recessive.
In the example of practicing exercises, we see that specific combinations, like AAbb or AABB, determine a range of colors including gray, yellow, black, and cream. Additionally, the interaction between these genes can be impacted by another gene (denoted as 'C' in the exercise) that either allows color expression or results in albinism.
The complexity arises because not only do individual genes matter, but also how they interact with others, resulting in various phenotypes. This makes coat color an excellent study case for understanding genetic interactions.

Albinism in Rats

Albinism in rats is a condition resulting from a specific genetic makeup where the animal lacks pigmentation, causing them to appear white or albino. This occurs because of the presence of homozygous recessive alleles at the C gene locus, represented as 'cc'.
In the context of coat color genetics, even if rats carry alleles for other colors (like A or B alleles), the 'cc' genotype will dominate, leading to a lack of color, or albinism.
This phenomenon is a great example of how a single gene can overshadow others, demonstrating epistasis, where one gene interferes with the phenotypic expression of another. Albinism, therefore, serves as a key study area for understanding gene interactions and dominance within genetic models.