Variables:
Part 1:
Independent:
Phenotypes of parents
Dependant:
Genotype of parents
Controls:
The same two coins (which are both the same type of coin—a penny) are flipped.
The coins are flipped on the same surface.
The same source of information is used to determine the genotypes.
Note: To a certain extent, the single definite independent variable is the phenotype of the parents. Though biologically in nature the phenotype is dependent on the genotype, in this experiment, the phenotypes of the parents are known for certain and the genotype must be determined by probability. Thus, the genotype is dependent on the phenotype.
Part 2:
Independent:
Genotypes and phenotypes of parents
Dependent:
Genotypes of offspring
Controls:
The same two coins (which are both the same type of coin—a penny) are flipped.
The coins are flipped on the same surface.
The same source of information is used to determine the genotypes.
Part 3:
Independent:
Genotypes of offspring
Dependant:
Phenotypes of offspring
Controls:
The same source of information is used to determine the genotypes.
Note: In this portion of the experiment, the phenotype of the offspring is directly dependant on the genotype. This is the natural order of events.
Materials:
1 copy of the Human traits information handout
1 data table
2 pennies
1 flat surface
1 writing utensil
1 hypothetical mother
1 hypothetical father
Procedure:
Part 1: Determining the Phenotype and Genotype of the Parents
- Using the Human traits information handout, asses the phenotypes of the mother and father in regards to the following: gender; facial shape(round or square); chin (very prominent or less prominent); ear lobes (attached or detached); cleft chin (absent or present); hair curl (straight, wavy, or curly); ‘Widow’s peak’ (present or absent); hair colour (black, red, brown, regular blond, dark blond, or light blond); eyebrow thickness (thick or fine); eyebrow separation (separated or connected); eyebrow colour (darker than hair, lighter than hair, or same colour as hair); eye distance (close together, average distance, or far apart); eye size (Large, average, small); eye shape(almond or circularly shaped); eye slant (horizontal or upward slant); eye colour (dark brown, brown, brown with green portions, grayish blue, green, dark blue, or light blue) ; eyelash length (long or short); mouth length (long, average, or short); lip thickness (thick or thin); presence of Hapsburg lip (distinctly protruding, slightly protruding, or absent); dimples (present or absent); nose size (large, average, or small); freckles (present or absent); blood type(A, AB, B, or O); colour blindness of seeing red or green (affected, carrier, or not affected); Cystic fibrosis(affected, carrier, or not affected); and Achondroplasia(affected, carrier, or not affected). Record your observations in the data table.
- Using the Human traits information handout, translate these phenotypes into genotypes and enter them into the data table.
- For traits which possess more than one gene in order to be expressed, each parent must flip their coin. A head will denote a dominant allele and a tail denotes a recessive allele. For example, if the father has a cleft chin, the gene that causes this could be CC or Cc. Therefore, the father shall flip his coin. If the result is a head, his gene is CC. If the result is a tail, his gene is Cc.
Part 2: Determining the Genotypes of the Offspring
- In each of the child’s genes, the mother will contribute one allele and the father will donate another allele. For each of the traits where a parent (or both) are homozygous, it is not necessary to flip a coin to determine the allele that will be donated, the two alleles are the same.
- If the parent is heterozygous for a trait, each partner will flip their coin. Heads will indicate donating the dominant allele and tails will indicate contributing the recessive allele.
- To determine the sex of the child, the father shall flip his coin. Heads indicates a Y chromosome and tails denotes an X chromosome.
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To determine the blood group, the pair of coins shall be flipped twice. Two heads indicate IA. Two tails indicate i. One head and one tail indicates IB.
- Record all observations.
- Repeat steps iv to viii for the second child (or trial).
Part 3: Determining the Phenotypes of the Offspring
- Using the Human traits information handout, determine the phenotype of each child.
- Illustrate the appearance of each child with two portraits.
- Construct a family pedigree of the P, F1, F2, and F3 generations by making predictions about possible future generations.
Observations:
Table I: Genotype and Phenotype Information of P and F1 Generations
Analysis:
Image I: Pedigree of Family- Occurrence of Cystic Fibrosis
The image below portrays a possible pedigree of cystic fibrosis in the P, F1, F2, and F3 generations of the family which was developed in the experiment. The partners of the F2 and F3 generations were selected in order to elucidate an array of results.
Image II: Punnett Square of Nose Size (Both parents are homozygous)
The image below illustrates the probability involved in the process of determining the genotype of offspring.
Therefore it is 100% certain that the offspring will possess an average sized nose.
Image III: Punnett Square of Presence of a Widow’s Peak (One parent is homozygous, one parent is heterozygous)
The image below illustrates the probability involved in the process of determining the genotype of offspring.
Therefore there is a 50% probability of the child having a Widow’s peak and a 50% chance of the absence of a Widow’s peak.
Image IV: Punnett Square of Hair Curl (Both parents are heterozygous)
The image below illustrates the probability involved in the process of determining the genotype of offspring.
Therefore there is a 25% chance of the hair of the offspring being curly, a 25% chance of the hair being straight, and a 50% chance of the hair being wavy.
Conclusion:
Evidently, probability plays a predominant role in genotyping and phenotyping. This is elucidated by the fact that (other than with traits that both parents possess homozygous genes for) the genotype of each child was determined by flipping a coin. This is reflected in nature, as if both parents are homozygous, then the offspring will naturally possess an allele for the expressed trait in each parent. Moreover, if the parents are heterozygous, the number of possibilities for the genotype of the offspring increases, and thus, the probability of each possibility is decreased. This is evident in Images II, III, and IV. When the genes of both parents are homozygous, the inherited alleles of the offspring are known, and thus, there is only one resultant genotype (which is 100% certain, or probable). When one parent is homozygous and the other is heterozygous (Image III), the same division is reflected in the offspring as there is a 50% probability of the child possessing a homozygous gene and a 50% probability that the gene is heterozygous. Contrastly, when the parents are both heterozygous, there is a 50% chance of the offspring having a heterozygous gene, a 25% prospect of the child possessing two recessive alleles and a 25% probability of the child possessing two dominant alleles. Thus, the simple mathematics of probability are reflected in this simulation.
These probabilities, however, neglect to consider the possibility of error and mutations in the processes of mitosis and meiosis which may alter the genes. Thus, there is an indeterminate degree of error in the percent probabilities.
As illustrated in Image I, it evident that pedigrees can be utilized in order to determine the risk involved in inheriting diseases or merely the prospect of inheriting certain attributes, such as eyelash length.
As predicted, the genotypes of the two hypothetical parents differ greatly as the individuals did express contrast phenotypes. Moreover, due to the evident phenotypic variation between the two selected hypothetical parents, it was postulated that the offspring would possess intermediary genomes due to the simple mathematics of probability, and thus, would express contrast phenotypes. This prediction is supported by Images V and VI and Table I which portray the great phenotypic and genotypic variations of Child I and Child II. Additionally, the polygenic attributes were predicted to vary more. This prediction was evidently correct by considering that both children had brown hair, despite that neither parent had this colour of hair.
Conclusively, it is evident that probability is fundamental in the process of copulation.
