Biology Forum

Questions for group discussion:

Draw the cell on the right (note that the letters indicate the gene and alleles present in each chromosome, show those letters on every drawing) as it goes from the G1 phase, to the S phase, G2 and then every phase in meiosis. Indicate the main things that happen to its chromosomes at each stage (label: sister chromatids, homologous chromosomes, Meiosis I, Meiosis II, identify which cells are haploid and which are diploid). Draw it in paper and upload a photo or scan, post it as an image not as a file to the discussion post (use the image icon to upload).
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Based on the diagram you drew above: A) Which events are unique to meiosis. B) The main purpose of sexual reproduction is to produce genetic variation in the offspring. Explain at least 3 ways in which meiosis promotes genetic variation. C) Explain which events in meiosis are responsible for the principle on segregation and which events are responsible for the principle of independent assortment.

1. Given what you have learned about the principle of independent assortment and how meiosis induces variation in the genetic composition of gametes, discuss the following: Some plants can reproduce asexually (by mitosis they produce structures that can break apart from the parent plant and sprout as an independent plant with the same genetic composition as the parent plant) and sexually (by meiosis, ultimately producing male and female gametes). However, many plants can do self-fertilization (male and female gametes from the same parent plant fertilize to form a zygote). Do you think that the offspring created through self-fertilization are genetic clones of the parent, just as it occurs during asexual reproduction? Explain your choice.

A) When predicting the phenotype of the offspring from a dihybrid cross, why is it so important that each gene is located in a different chromosome? B) You crossed a tall plant that produces purple flowers with a short plant that also produces purple flowers. Assume tall and purple flower are dominant traits. The 2165 offspring were: 100% tall plants, ¾ of the plants produced purple flowers and the remaining 1/4 of the plants produced white flowers. What were the possible genotypes of the parents???

For the pedigree on the right, individuals affected with the genetic condition are indicated by the shaded symbols. A) Based on this pedigree, what type of inheritance does this genetic condition have (dominant, recessive, sex-linked)? Explain. B) What is the genotype of the parents? C) What makes an allele dominant or recessive? image link

Mendel was very lucky to study traits that follow simple hereditary rules. We now know that there are multiple factors that can interfere with the expected Mendelian ratios. A) Explain 3 genetic mechanisms that can prevent Mendel’s results from being observed and B) give an example of each.