Module 6

Module 6—Mendelian Genetics: The Transmission of Traits to the Next Generation

Reflect and Connect

The analysis of linked-gene crosses for recombinant phenotypes and calculation of recombinant frequencies is used to develop gene maps for traits. The hypothesis is that the greater the amount of crossing over between genes, the further apart those genes are on a chromosome. Map units are used to locate genes along the chromosome to form a gene map. Gene maps can provide an understanding of how or why certain traits tend to move together while others may not, even if found on the same chromosome.

To ensure your mastery of linked genes and chromosome mapping, answer the following Self-Check questions.

Self-Check

Use the following information to answer SC 3 and SC 4.

SC 3. During meiosis, which of the following pairs of genes has the greatest chance of being separated by crossing over?

1. (m) and (d)
2. (ne) and (p)
3. (m) and (lc)
4. (p) and (o)
   

Use the following additional information to answer SC 4.

SC 4. The cross-over frequency between genes O and S is

1. 6%
2. 29%
3. 31%
4. 97%

Use the following information to answer SC 5.

Numerical Response

SC 5. On human chromosome 6, the order of the genes numbered above is ___, ___, ___ and ___.

SC 6. What is the approximate crossover frequency between the rhesus blood group gene and the ragweed sensitivity gene?

1. 1.5%
2. 10.5%
3. 19.5%
4. 22.5%

Use the following information to answer SC 7.

Gregor Mendel examined the inheritance of two traits in pea plants: seed coat texture and colour. Seed coat texture can be represented as S–smooth and s–wrinkled, and seed coat colour can be represented as Y–yellow and y–green. SSYY plants were crossed with ssyy plants to yield F1 pea seeds that were all smooth and all yellow. By crossing plants grown from these F1 seeds, Mendel obtained four different phenotypes of F2 seeds:

• smooth, green seeds
• wrinkled, green seeds
• smooth, yellow seeds
• wrinkled, yellow seed

SC 7. If the traits for seed coat texture and seed coat colour had been located close together on the same chromosome, Mendel might not have conceptualized

1. gene pairs
2. dominance
3. the law of segregation
4. the law of independent assortment

The Human Genome Project was one of the largest genetic projects ever completed. It involved the participation of public universities and private companies from around the world, and took over 13 years to complete. Completed, the Human Genome Project represents a relative map of all human genes found on all chromosomes.

However, the project was not without controversy. In order to encourage private companies to take part, these companies were allowed to patent certain tests that can locate specific genes in people, such as genes related to the possibility of developing cancer. As a result, hospitals and labs have to pay these companies for the right to conduct tests to determine if a person is at risk of developing cancer due to family history. In addition, tests for the presence of certain genes may also provide information about other genes that were not originally considered. This kind of information has the potential to be harmful to the individual if it became available to insurance companies, or to a person’s place of employment.

Discuss

Research the issue of private industry in genetic research and/or testing. Take a position on whether or not private industry should be allowed or encouraged to participate in the advancement of the field of personal health. Communicate your position to your peers and instructor on a class discussion board, or in whatever manner your teacher sets up for you. Engage your classmates in the defense of your position, and challenge others to defend their positions. Revise your response after your discussion with your classmates.

Module 6: Lesson 9 Assignment

Retrieve your copy of Module 6: Lesson 9 Assignment that you saved to your computer earlier in this lesson. Paste your revised discussion posting into the D 1 text box. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.

Reflect on the Big Picture

Remember wondering in the Big Picture why some family members look alike. If they had dark hair, they also seemed to have curly hair, brown eyes, and a dimpled chin. Using the principles of linkage, you should be able to explain how these characteristics might have been inherited together. Using the principles of crossing over you should also be able to explain why some family members seem to have little resemblance to their parents. 

The linkage of genes on chromosomes tends to reduce variability in offspring. Certain genes, and their expression, tend to move together. However, crossing over of chromosomes in meiosis acts as a counter to this trend. Crossing over will increase variability in offspring by creating chromosome combinations not seen in parents.

Going Beyond

One of the essential skills in genetics is learning to apply what you know to new situations. For a challenge, do a web search using the terms “biology + Arizona + edu + mendelian genetics + problem sets + sex-linked inheritance.” Work through the second set of sex-linked inheritance problems. In this set, each question builds on the next, and the last question requires an understanding of linked genes.

Module 6: Lesson 9 Assignment

Submit your completed Module 6: Lesson 9 Assignment to your teacher for assessment.