9: Genetics
- Page ID
- 24790
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- 9.1: Introduction
- In the mid-1800s, an Augustinian friar named Gregor Mendel formalized quantitative observations on heredity in the pea plant. He undertook hybridization experiments that utilized purebred or true-breeding plants with specific qualities over many generations to observe the passage of these traits. Some of these physical traits included: seed shape, flower color, plant height, and pod shape.
- 9.2: Bitter Taste (Activity)
- Some of our personal preferences arise from the way we were brought up. Culture plays a role in our likes and dislikes. Likewise, our experiences play a role in how we respond to certain stimuli. In our search for nutritive compounds, we have learned to avoid things that don’t taste good. Bitter things have a tendency to be associated with toxic compounds in nature. Hence, something bitter might make us learn to avoid this food item in the future.
- 9.3: Sex-linked Genes
- For the most part, mammals have gender determined by the presence of the Y chromosome. This chromosome is gene poor and a specific area called sex determining region on Y (SRY) is responsible for the initiation of the male sex determination. The X-chromosome is rich in genes while the Y-chromosome is a gene desert. The presence of an X-chromosome is absolutely necessary to produce a viable life form and the default gender of mammals is traditionally female.
- 9.4: Probability and Chi-Square Analysis
- Punnett Squares are convenient for predicting the outcome of monohybrid or dihybrid crosses. The expectation of two heterozygous parents is 3:1 in a single trait cross or 9:3:3:1 in a two-trait cross. Performing a three or four trait cross becomes very messy. In these instances, it is better to follow the rules of probability. Probability is the chance that an event will occur expressed as a fraction or percentage.
- 9.5: Non-Mendelian Genetics
- During Mendel’s time, people believed in a concept of blending inheritance whereby offspring demonstrated intermediate phenotypes between those of the parental generation. This was refuted by Mendel’s pea experiments that illustrated a Law of Dominance. Despite this, non-Mendelian inheritance can be observed in sex-linkage and co-dominance where the expected ratios of phenotypes are not observed clearly.
- 9.6: Hardy-Weinberg and Population Genetics
- The Hardy-Weinberg principle is a mathematical model used to describe the equilibrium of two alleles in a population in the absence of evolutionary forces. This model was derived independently by G.H. Hardy and Wilhelm Weinberg. It states that the allele and genotype frequencies across a population will remain constant across generations in the absence of evolutionary forces.