Bio-Pac 06: Objective 01-06 Flashcards
Objective 1. Describe Mendel’s experiments with tall and short pea plants.
Mendel studied one trait at a time to control variables and he analyzed his traits mathematically. He controlled the variables by using tall pea plants that were from populations of pea plants that had been tall for generations, and short pea plants that were from populations of pea plants that had been short for generations. Mendel used the plants to produce new plants by crossing. The first generation was all tall and none were short. The second generation which was formed by the first generation crossing over with each other by self-pollination formed offspring three-fourths of which were tall and one-fourth which was short. His experimenting showed that one trait seemed to disappear in the first generation and reappear in the second generation. His experiments with tall and short pea plants showed that the first generation had a gene disappear and the same gene reappear in the second generation, rule of unit factors—alleles, rule of dominance, and law of segregation.
Objective 2. State the rule of dominance. Describe an example.
Mendel observed a dominant and recessive trait. We know that the allele for tall plants is dominant to the allele for short plants. Pea plants that had two alleles for tallness were tall, and those that had two alleles for short were short. Plants that had two alleles for tallness one for shortness were tall because the allele for tallness is dominant to the allele of shortness.
Objective 3. State the law of segregation. Describe an example using a seed plant which is heterozygous round.
Two alleles for each trait must separate when gametes are formed, meaning that a parent passes on at random only one allele of each trait to their offspring. A seed plant that is heterozygous round means that its genotype is Rr , because it has the dominant allele of being round (R) and recessive allele of being wrinkled (r). This means that the seed plant had parents that were RR and Rr or Rr and Rr, because by the law of segregation these two different combinations of parents could both result in a seed plant with heterozygous round (Rr)
Objective 4. State the law of independent assortment. Describe an example using genes for wrinkled, round, yellow, and green.
Genes from different traits are inherited independently of each other. When a pea plant with the genotype RrYy produces gametes, the alleles R and r will separate from each other (the law of segregation and the law of independent assortment) and Y and y will separate from each other. These alleles can then recombine in four different ways.
Objective 5. Describe how a punnet square can be used to predict the probable results of genetic crosses. Show an example using a cross involving free and attached ear lobes.
In 1905, Reginald Punnett (English biologist), devised a shorthand way of finding the expected proportions of possible genotypes in different offspring. A punnett square takes into account of the fact that fertilization occurs at random, as Mendel’s law of segregation states. By knowing the genotypes of the parents, a Punnett square will allow you to predict the possible genotypes of their offspring. Free hanging earlobes are the dominant allele (F) while the attached earlobes are the recessive allele (f).
