Module Instructions: Mendel and the Gene

Pre-Lab: Mendel and the Gene

Watch the Pre-Lab video to prepare you for the lab.

Lab: Mendelian Genetics

There are no materials needed for this lab.

Below are some suggestions for commonly made mistakes in the lab.

  • In question 8, which of the principles that Mendel discovered explain separating the alleles in the Punnett Square. Choose between: 1) Principle of Dominance, 2) Principle of Segregation or 3? Principle of Independent Assortment.

  • In questions 9 and 10, you are to report on the genotypic and phenotypic ratio. In this case the genotypes are FF, Ff and ff. Since the cross FF x ff will only provide the genotype Ff. You would report the genotypic ratio as “all Ff” or 100% Ff. In this case there are only two phenotypes: purple and white. Since purple is dominant to white. All of the Ff will appear purple, meaning the phenotypic ration is: all purple.

  • In question 9, set up the Punnett Square with the monohybrid cross (Ff x Ff). The genotypic ratio would be the combination of FF, Ff and ff. If you complete the Punnett Square correctly, you will see that there is one FF, two Ff and one ff. Therefore the phenotypic ratio would be 1FF: 2Ff: 1ff.

  • In question 10, you need to interpret the genotypes. Since both FF and Ff appear purple, three out of four would appear purple and only one (ff) would appear white. So you would answer 3 purple: 1 white.

  • In questions 14 and 15, you will report on the phenotypes for flower color (purple or white) and seed color (green or yellow). If you look at Table 1, you can ascertain that purple is dominant to white for flower color, and yellow is dominant to green for seed color.

  • For question 16, you will report on the expected phenotypic (physical characteristic) ratio for both flower color and seed color as predicted by depenedent assortment. Remember that in this case the dominant alleles for flower color (purple) and seed color (yellow) stay together. Likewise the recessive alleles for flower color (white) and seed color (green) stay connected. In other words, when FfSs undergoes meiosis, the only possible combinations are FS and fs. The cross should look like this:

 
 

  • For question 17, independent assortment (in contrast) predicts that a dihybrid (FfSs) can produce all combinations of alleles (FS, Fs, fS and fs). For question 18, out of the 16 boxes be sure to report on the combination of the phenotypes: 1) Purple/Yellow, 2) Purple/Green, 3) White/Yellow and 4) White/Green.

  • For question 20, we always start with two parents that have the same phenotype, but have a child that is different. In this case, we know with certainty that both parents must be heterozygous (Aa) and the child is recessive (aa). This is the only way this is possible. Each parent donated a recessive allele: a.

 
 

  • Once we identify the recessive phenotype, we know that all individuals with that phenotype have the genotype: aa. Next let us try to determine the genotype of their other child: 5.

 
 

  • Consider 5. In this case we know that the individual is expressing the dominant characteristic. In other words, the individual is either AA or Aa. Since both parents are Aa, individual 5 could either be AA or Aa. Without any further pedigree information, we can not determine which. So we would write that as AA or Aa (or A?).

 
 

  • Consider 8 and 10. In this case, we know the partner of 8 is aa and one of their children are aa. The only way that child is aa is if one of the recessive alleles (a) came from 8. Therefore 8 must be Aa. In the case of 10, she has the dominant phenotype. So she is either AA or Aa. However, the male parent (aa) can only provide a recessive allele (a). Therefore, 10 must also be heterozygous, Aa.

 
 

  • Consider 3 and 4. They are both dominant phenotypes: AA or Aa. They have a child that is a heterozygous: Aa. Therefore, one of the parents provided a recessive allele: a. However, without any further information we do not know which parent that is. 3 and 4 could be AA or Aa.

 
 

  • Use this strategy to help you fill out the last page of the lab.

Post-Lab: Mendel and the Gene

Once you finish with the lab, complete the post-lab by the due date in the class calendar.