When scientists first observed chromosomes in mitosis and meiosis, it was suggested that chromosomes were likely to carry the genetic material. Some direct evidence came from studying X linked genes in fruit flies: the traits (such as a trait for eye color) followed the X chromosome.  When researchers found genetic evidence for recombination, they wanted to see whether they could correlate physical crossing over on the chromosome withe genetic recombination.  In order to do, this scientists took advantage of some characteristics of corn chromosomes.

To understand their research it helps to review a few key corn traits

The colored trait is coded for by a dominant allele (C) and the recessive allele (c) gives yellow kernels

A second gene called Waxy effects the type of starch in the kernels.  Wx is a dominant allele that makes 2 kinds of starch (Amylose starch and amylopectin) while corn plants homozygous for the recessive allele (wx) make only amylopectin. The Wx gene and C gene are on chromosome 9 of corn.
Corn chromosomes can also have knobs, which are darkly staining regions at the end of chromosomes. However, for a given chromosome (such as chromosome 9) the knob may or may not be present and it acts like a genetic marker. In other words, a corn plant that has knobs on both chromosome 9s will pass this chromosome to all of its offspring. If such a plant is crossed to a strain that lacks the knob, then the offspring will be heterozygous for the knob trait.  Below is a picture of knobs in corn chromosomes. Chromosome Knobs are shown below:

the first critical experiment involved the cross shown below in which plants that were heterozygous for the Knob and the C gene were crossed to plants that lacked the knob and were homozygous for the recessive c allele. These experiments were carried out by Harriet Creighton and Barbara McClintock

From this experiment, the researchers concluded that the chromosome 9 Knob and the C gene were on the same chromosome and linked closely.

The second experiment used a strain of corn that was heterozygous for the Wx gene, the C gene and the knob. Creighton and McClintock carried out the following cross:

In your own words, state what the results of this cross says about the relationship between recombination and physical crossing over.

Image Credits

FIGURE 3. Carmine-stained pachytene chromosomes of the 441123 × 444331 hybrid showing cytologically visible knobs on chromosomes 3(B), 5(C), 6(F), 7(G), 8(I), and 9(J)

From Mondin etal

Karyotype variability in tropical maize sister inbred lines and hybrids compared with KYS standard line

http://journal.frontiersin.org/article/10.3389/fpls.2014.00544/full

Image URL: http://www.frontiersin.org/files/Articles/111039/fpls-05-00544-HTML/image_m/fpls-05-00544-g003.jpg

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Maize

https://en.wikipedia.org/wiki/Maize

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Maizmorado.png

Malosh

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Question

Go to the following site and go through the animation and the problems
Genetic Code and Protein Synthesis Animation

Answer these questions for review

https://goo.gl/forms/Ns6mxalC88mkBCKL2

Post the URL to your fakebook site so that others can view it.  Post in the Comment section below.

Welcome to My blog Sites. This is your first post. Edit or delete it, then start blogging!

1. Find an article that has to do with some aspect of Biotechnolgy
2. Give a short description describing what was accomplished and how they did it.  Use your own words!
3. Put the URL and your description under the comments here

The elucidation of the structure of the double helix provided a hint as to how DNA divides and makes copies of itself. This model suggests that the two strands of the double helix separate during replication, and each strand serves as a template from which the new complementary strand is copied. What was not clear was how the replication took place. There were three models suggested (Figure): conservative, semi-conservative, and dispersive.

In conservative replication, the parental DNA remains together, and the newly formed daughter strands are together. The semi-conservative method suggests that each of the two parental DNA strands act as a template for new DNA to be synthesized; after replication, each double-stranded DNA includes one parental or “old” strand and one “new” strand. In the dispersive model, both copies of DNA have double-stranded segments of parental DNA and newly synthesized DNA interspersed.

Meselson and Stahl were interested in understanding how DNA replicates. They grew E. coli for several generations in a medium containing a “heavy” isotope of nitrogen (¹⁵N) that gets incorporated into nitrogenous bases, and eventually into the DNA (Figure).

Go to http://www.hhmi.org/biointeractive/gender-testing-athletes

Go through the activities in this site and answer the following questions (some of them are in the site itself)

1. Can a test determine an individual’s biological sex? And can testosterone produced by an athlete’s own body provide an unfair advantage?

2. At the bottom of the section on development is a graph showing testosterone levels for male and female athletes. Most female athletes have less than 5 nm/L of testosterone, but a few have as high as 30 nmol/L which is above the average for male athletes. Which genetic condition(s) can cause XX individuals to have high testosterone levels?

(3) The AR gene codes for a transcription factor which is only functional when testosterone is present.  Based on what you know about transcription factors and about sex determination explain

(A) Why do XY individuals with a mutation in the AR gene develop as females despite having male levels of testosterone?

(B) Would you expect such individuals to be more muscular than an average female?

(4) Do the case studies for the sprinter and the swimmer. Should they be eligible to compete? Explain your answer.

Post the URL of the project you made here. Post it as a comment on this blog.

Read the following:

Then answer the following questions:

Would you expect the 2 daughters of the mother in the article to have a chance to have sons with muscular dystrophy? Explain.

Should we as a society spend more or less on diseases like Duchenne muscular dystrophy? Note that Duchenne Muscular dystrophy is fairly common compared to most single gene diseases, but much rarer than conditions like heart disease or autism.

If a cure is found but it is very expensive, should it be available to everybody? Why or why not?

A doctor in that article made (what I believe) to be a serious ethical error. What was it? Discuss.

Write your answers as a reply in the comments section