Genes and Alleles

This week mainly consisted of learning about genes and alleles. There are two alleles in one gene that is located in a certain position on a certain chromosome. There are two types of alleles: Dominant and recessive. One organism can either be homozygous dominant, heterozygous, or homozygous recessive.


Here is a simple picture demonstrating the dominant and recessive alleles. The green little y’s are recessive and the larger Y is dominant, therefore two of the bananas will be yellow heterozygous and two will be green dominant recessive. Here is also a link to the bozeman video on punnett squares.

The definition of a punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment. The diagram is used by biologists to determine the probability of an offspring having a particular genotype.

After the punnett square, we began to learn about the Hardy Weinberg Equation. Honestly, this confused me and still confuses me! I know the two different forms are p + q = 1 and p^2 + 2pq + q^2 = 1, but what do they do? I also found myself to be really confused on the difference between the frequency of a dominant/ recessive allele versus the frequency of a homozygous dominant/heterozygous etc. Even after doing the sample problems in the Population Genetics lab, I am still confused. How do these two formulas relate with each other?

Although I was confused with this, I did learn more through the Population Genetics lab. I discovered that Hardy Weinberg equilibrium is when allele frequencies do not change from generation to generation. Five conditions that must be met to maintain a population in the Hardy Weinberg Population is

  1. There has to be random mating
  2. There is no gene flow and migration
  3. No natural selection
  4. There are no mutations
  5. There is a large population, counteracting the change of genetic drift. (Note: genetic drift is the variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce.)

Through the trials, I discovered that there are different outcomes in a population under different circumstances. Throughout the different trials of mating, I discovered that a population may look completely different after several generations. This random mating allowed genetic variation in the population (1.A.3). I think for me it was helpful to do the main calculations as a class. It’s nice to confirm if I’m doing them right/ and also learn what I’m doing wrong.

Besides the lab, we also did a phylogenetic worksheet. Here, I learned that DNA sequence comparison and anatomical comparison are two ways to discover how two organisms are related. DNA sequence is more reliable and objective than anatomical features (1.B.2). maxresdefault

Here is a picture of a cladogram and the arrow showed is where there is a common ancestor between the species it’s connected to. Overall, I have learned a lot this week, however, I do need more clarification on several things: Hardy Weinberg equations, calculating allele frequencies after several generations, and how to compare the DNA sequences from two different species.


3 thoughts on “Genes and Alleles

  1. damn audrey nice post. I am also sort of confused about hardy weinberg! all I can say is that if you look at the punnet square and multiply the p’s and q’s it results in the second equation. Hopefully that helps sort of


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