Bio 107 Cell Division and Mendelian Genetics

Mitosis

The first half of this week’s lab is primarily an opportunity to observe cells at different stages of mitosis. You will examine a slide containing a longitudinal section of an onion root tip. Within the root, many cells are undergoing rapid cell division. Therefore, a large number of cells on the slide are at some phase of mitotic division. Your task is to observe and be able to identify cells in particular phases of mitosis.

Interphase

Prophase

Metaphase

Anaphase

Telophase

Mendelian Genetics

In this part of today’s lab, we will observe two genes in corn that are determined by simple Mendelian inheritance. Because corn kernels are developing embryos of corn, we can use the kernels of a single cob of corn as the representative offspring of a particular reproductive event of two corn plants (ie. each kernel is a “baby” of the corn “parents”). These characters are observable in the kernels of corn cobs. The two character states of the character “Kernel Color” are dark purple (P = dominant) and yellow (p = recessive). The two character states for “Kernel Shape” are smooth (S = dominant) or wrinkled (s = recessive). These genes are located on different chromosomes and therefore are inherited independently of one another (illustrating Mendel’s Law of Independent Assortment)

Part I: Tracking a single gene

Examine a display box marked “Monohybrid Cross”. Note the sections of corn cobs and diagram illustrating the relationships of each cob in the box. Also notice the ratio of purple to yellow kernels in each cob.

On a corn cob with both purple and yellow kernels, count 100 kernels from the same row(s) making note of the number of each color kernel (they are either purple or yellow). What is the approximate ratio of purple to yellow kernels? Working backward from a Punnet Square, hypothesize what the genotype of each parent plant was. We can do this by deducing what kind of gametes would be required to produce the phenotypes observed in the corn cob. Note those gametes along the left and top of the Punnet Square. From the gametes necessary to produce the observable phenotypes, what are the genotypes of the parents?

Part II: Tracking a two genes

Examine a display box marked “Dihybrid Cross”. Note the sections of corn cobs and diagram illustrating the relationships of each cob in the box. Also notice the ratio of purple and round, purple and wrinkled, yellow and round, and yellow and wrinkled kernels in the heterozygous cob.

On a corn cob with purple and round, purple and wrinkled, yellow and round, and yellow and wrinkled kernels, count 100 kernels from the same row(s) making note of the number of each type of kernel. What is the approximate ratio of each type of kernel? Working backward from a Punnet Square, hypothesize what the genotype of each parent plant was. We can do this by deducing what kind of gametes would be required to produce the phenotypes observed in the corn cob. Note those gametes along the left and top of the Punnet Square. From the gametes necessary to produce the observable phenotypes, predict the genotypes of the parents?