Question

In peas, tall (D) is dominant to dwarf (d) and yellow cotyledons (G) is dominant to green (g). If a tall, heterozygous pea plant with green cotyledons is crossed with a dwarf pea plant heterozygous for yellow cotyledons, what will be the phenotypic results in the progeny?

Short answer

The phenotypic results in the progeny will be an equal distribution of 1:1:1:1 for Tall and Yellow, Dwarf and Yellow, Tall and Green, and Dwarf and Green respectively.

Step-by-step solution

Determine the genotypes of the parental plants

First, we must convert the given phenotypes of the parental plants into genotypes. The tall pea plant has green cotyledons, so it must represent the genotype Ddgg (heterozygous tall, homozygous recessive green). The dwarf pea plant has heterozygous yellow cotyledons, so its genotype must be ddGg (homozygous recessive dwarf, heterozygous yellow).

Set up the Punnett squares

To set up the Punnett squares, we will first find out all the possible gametes that these two plants can produce. For the tall plant (Ddgg), it can produce two kinds of gametes: Dg or dg. For the dwarf plant (ddGg), it can also produce two kinds of gametes: dG or dg. Now we can set up a 2x2 Punnett square to find out all the possible genotypes of the offspring.

Fill in the Punnett squares

Fill in the Punnett squares by combining the gametes produced by the parental plants to generate the offspring's genotypes: | | Dg | dg | |----|----|----| | dG | DdGg | ddGg | | dg | Ddg | ddgg |

Determine the phenotypes of the offspring

Now that we have all the genotypes of the offspring, we can determine their phenotypes based on which traits are dominant: - DdGg: Tall and Yellow (hybrid) - ddGg: Dwarf and Yellow (heterozygous for yellow) - Ddg: Tall and Green (heterozygous for tall) - ddgg: Dwarf and Green (homozygous recessive for both traits)

Calculate the phenotypic ratios

To find the phenotypic ratios, count the number of offspring with each phenotype and then divide by the total number of offspring: - Tall and Yellow: 1/4 - Dwarf and Yellow: 1/4 - Tall and Green: 1/4 - Dwarf and Green: 1/4 Thus, the phenotypic results in the progeny will be an equal distribution of 1:1:1:1 for Tall and Yellow, Dwarf and Yellow, Tall and Green, and Dwarf and Green respectively.

Key concepts

Genotype to Phenotype Conversion

Understanding how genotypes translate to phenotypes is crucial in genetics. A genotype is the genetic makeup of an organism, while a phenotype is the observable trait. Genes exist in different forms called alleles, which can be either dominant or recessive. The dominant allele overshadows the recessive allele's effect.

During genotype to phenotype conversion, the combination of alleles determines the organism's trait. For example, for plant height in peas, the allele for tall (D) is dominant over dwarf (d). Therefore, a plant with a genotype of DD or Dd will display the tall phenotype because the presence of at least one dominant D allele ensures the tall trait.

Similarly, with cotyledon color where yellow (G) is dominant over green (g), a plant having genotypes GG or Gg will exhibit yellow cotyledons. The only way to have green cotyledons is by having the genotype gg. By predicting the possible genotypic outcomes, using tools like Punnett squares, we can forecast the phenotypic offspring distribution.

Mendelian Inheritance

Mendelian inheritance refers to the patterns of inheritance for traits as established by Gregor Mendel in the 19th century. These foundational principles help us predict how traits pass from one generation to the next. Mendel's laws include the Law of Segregation and the Law of Independent Assortment.

The Law of Segregation states that alleles separate during gamete formation, ensuring that each gamete carries only one allele for each trait. When fertilization happens, offspring receive one allele from each parent, reconstituting the pair.

The Law of Independent Assortment proposes that genes for different traits segregate independently of one another in the formation of gametes. This is assuming the genes are on separate chromosomes or far enough apart on the same chromosome to behave independently. These laws form the basis of understanding inheritance patterns within Punnett squares and phenotypic ratios.

Dihybrid Cross

A dihybrid cross is an extension of Mendelian inheritance that involves two traits at once. It describes a mating experiment between two organisms that are identically hybrid for two traits. For example, when a pea plant with genotype DdGg crosses with another DdGg plant, where 'D' represents tall stems, 'd' dwarf stems, 'G' yellow cotyledons, and 'g' green cotyledons, we study the inheritance of both stem height and cotyledon color.

In doing so, we use a larger Punnett square to map the possible genotypes and thus predict phenotypic outcomes. Unlike a monohybrid cross, which only considers one trait and yields a 3:1 phenotypic ratio, a dihybrid cross gives rise to a 9:3:3:1 phenotypic ratio in the F2 generation under typical conditions of random mating and if the genes assort independently. This showcases the intricate dynamics of inheritance when multiple traits are at play.