# How Many Phenotypic Classes Result from Mendelian Crossings?

• tsoya
In summary, a Mendelian crossing problem refers to a genetic inheritance pattern first described by Gregor Mendel in the 19th century. The key principles of Mendelian genetics include the law of segregation and the law of independent assortment. These principles are used to understand and predict the inheritance of traits in offspring. To solve a Mendelian crossing problem, one must identify the genetic makeup of the parent organisms and use mathematical models to determine the possible combinations of alleles in the offspring. Some common challenges when solving Mendelian crossing problems include incomplete dominance and multiple alleles.
tsoya
I GOT IT nevermind thanks

i would really appreciate some help on this,
swamped with studies and my brain won't wrap around the mendelian gene crossings

here's one:
Base height of a plant is 10 cm. Four genes contribute to the height, and each dominant allele contributes 3 cm to height. If you cross a 10-cm plant (quadruply homozygous recessive) with a 34-cm plant, how many phenotypic classes will there be in the F2?

so i subtracted 10 from 34 =24. Dividing by 3 I get 8- so does that mean 8 dominant alleles present in one of the parents? don't really know where to go from there..and another:
In guinea pigs the brown coat color allele (B) is dominant over red (b), and the solid color allele (S) is dominant over spotted (s). The F1 offspring of a cross between true-breeding brown, solid-colored guinea pigs and red, spotted pigs are crossed. What proportion of their offspring (F2) would be expected to be red and solid colored?

-so is one of the F1 BBSS? And the other bbss? So I don't understand how I can get a red?

Last edited:
For the first question, the 10 cm plant is homozygous recessive for all four genes, so it has four alleles of bb and the 34 cm plant has four alleles of BB. In the F2 generation, these will combine to make 8 different phenotypic classes: Bb (12 cm), Bb (15 cm), Bb (18 cm), Bb (21 cm), BB (24 cm), BB (27 cm), BB (30 cm), and BB (33 cm).For the second question, the true-breeding parent guinea pigs are BBSS and bbss. The F1 offspring would all be BbSs, and when they are crossed in the F2, the expected ratio of red and solid colored offspring is 1:3. This means that for every red, spotted guinea pig you would expect three red, solid colored guinea pigs.

I am happy to help you understand the concept of Mendelian gene crossings. Mendelian genetics is the study of how traits are inherited from parents to offspring through the passing of genes.

In the first problem, we are dealing with height in plants and four genes that contribute to it. The dominant allele in each gene contributes 3 cm to the height. When you cross a 10-cm plant (quadruply homozygous recessive) with a 34-cm plant, you are essentially crossing two different genotypes - one with all recessive alleles and one with some dominant alleles. To determine the number of phenotypic classes in the F2 generation, you need to consider all possible combinations of alleles from the parents. In this case, there will be 8 different combinations of alleles in the F2 generation, resulting in 8 different phenotypes. This is because each parent can contribute either a dominant or recessive allele for each of the four genes, resulting in 2x2x2x2=8 different combinations.

In the second problem, we are dealing with coat color in guinea pigs. The dominant allele for coat color is B for brown and the dominant allele for pattern is S for solid. The F1 generation is the result of crossing two true-breeding parents, one with brown and solid coat (BBSS) and the other with red and spotted coat (bbss). This results in offspring with the genotype BbSs. In the F2 generation, when you cross these offspring with each other, you will get a 9:3:3:1 ratio of offspring with different coat colors and patterns. This means that 9/16 or about 56% of the offspring will be red and solid colored.

I hope this explanation helps you understand Mendelian gene crossings better. If you have any further questions, please do not hesitate to ask. Good luck with your studies!

## What is a Mendelian crossing problem?

A Mendelian crossing problem refers to a genetic inheritance pattern first described by Gregor Mendel in the 19th century. It involves the crossing of two parent organisms with different traits and the resulting inheritance of those traits in their offspring.

## What are the key principles of Mendelian genetics?

The key principles of Mendelian genetics include the law of segregation, which states that each individual has two copies of a gene, one from each parent, and these copies separate during the formation of reproductive cells. The second principle is the law of independent assortment, which states that the inheritance of one gene is not influenced by the inheritance of another gene.

## What is the purpose of Mendelian crossing problems in genetics?

Mendelian crossing problems are used to understand and predict the inheritance of traits in offspring based on the genetic makeup of their parents. By conducting crosses and analyzing the resulting offspring, scientists can determine the probability of certain traits being inherited and better understand the underlying genetic mechanisms at play.

## How do you solve a Mendelian crossing problem?

To solve a Mendelian crossing problem, you first need to identify the parent organisms and their genetic makeup, including the alleles for the trait of interest. Then, you can use Punnett squares or other mathematical models to determine the possible combinations of alleles in the offspring and the likelihood of each outcome.

## What are some common challenges when solving Mendelian crossing problems?

Some common challenges when solving Mendelian crossing problems include incomplete dominance, where one allele is not completely dominant over the other, and multiple alleles, where there are more than two versions of a gene. In these cases, additional genetic principles and tools may be needed to accurately predict the inheritance of traits.

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