4.3: Mendel’s Experiments
- Describe the different laws of genetics developed by Mendel.
- Utilize Punnett square to perform and follow a monohybrid cross.
- Explain how pedigree trees are constructed and how to use them to study genetic diseases.
Mendel’s Crosses
Mendel’s seminal work was accomplished using the garden pea, Pisum sativum , to study inheritance. This species naturally self-fertilizes, meaning that pollen encounters ova within the same flower. The flower petals remain sealed tightly until pollination is completed to prevent the pollination of other plants. The result is highly inbred, or “ true-breeding ,” pea plants. These are plants that always produce offspring that look like the parent. By experimenting with true-breeding pea plants, Mendel avoided the appearance of unexpected traits in offspring that might occur if the plants were not true breeding. The garden pea also grows to maturity within one season, meaning that several generations could be evaluated over a relatively short time. Finally, large quantities of garden peas could be cultivated simultaneously, allowing Mendel to conclude that his results did not come about simply by chance.
Monohybrid Crosses
Mendel performed hybridizations , which involve mating two true-breeding individuals that have different traits. In the pea, which is naturally self-pollinating, this is done by manually transferring pollen from the anther of a mature pea plant of one variety to the stigma of a separate mature pea plant of the second variety.
Plants used in first-generation crosses were called P , or parental generation , plants (Figure \(\PageIndex{1}\)). Mendel collected the seeds produced by the P plants that resulted from each cross and grew them the following season. These offspring were called the F 1 , or the first filial (filial = daughter or son), generation. Once Mendel examined the characteristics in the F 1 generation of plants, he allowed them to self-fertilize naturally. He then collected and grew the seeds from the F 1 plants to produce the F 2 , or second filial , generation. Mendel’s experiments extended beyond the F 2 generation to the F 3 generation, F 4 generation, and so on, but it was the ratio of characteristics in the P, F 1 , and F 2 generations that were the most intriguing and became the basis of Mendel’s postulates.
A monohybrid cross is one in which both parents are heterozygous (or a hybrid) for a single (mono) trait. The figure above shows the trait petal colour.
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Solution
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F1 : first filial generation in a cross; the offspring of the parental generation.
F2 : second filial generation produced when F 1 individuals are self-crossed or fertilized with each other.
Hybridization : process of mating two individuals that differ with the goal of achieving a certain characteristic in their offspring.
Monohybrid : result of a cross between two true-breeding parents that express different traits for only one characteristic.
P or P0 : parental generation in a cross.
Contributors and Attributions
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Samantha Fowler (Clayton State University), Rebecca Roush (Sandhills Community College), James Wise (Hampton University). Original content by OpenStax (CC BY 4.0; Access for free at https://cnx.org/contents/b3c1e1d2-83...4-e119a8aafbdd ).
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Query \(\PageIndex{1}\)