Module 6

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

Reflect and Connect

 

By adding knowledge of multiple alleles and incomplete dominance to what you have already learned about genetics, you have greatly expanded your ability to interpret phenotypes and predict inheritance. All this and you are still working with only one gene! When each chromosome has hundreds of genes, and humans have 23 chromosome pairs, think of all the possible variations that could exist.

 

Review your genetics flash cards and add the new terms from this lesson.

 

Self-Check

 

To apply your understanding of this lesson, complete the following Diploma Exam-style questions.

 

Several geneticists studied M. jalapa plants with deep crimson flowers and M. jalapa plants with yellow flowers. Cross-pollinating these plants produced plants with scarlet-red flowers (F1 generation).

 

These F1 plants were allowed to self-pollinate, and the resulting seeds produced M. jalapa plants with three different flower colours. Data similar to the following were collected for flower colour:

• 140 deep crimson
• 310 scarlet-red
• 160 yellow

SC 5. With respect to the alleles for flower colour, these results indicate which of the following?

1. X-linked inheritance
2. gene-linked inheritance
3. dominant-recessive inheritance
4. incomplete dominance
5. inheritance

SC 6. If a woman has blood type A, and her husband has blood type B, which of the following genotypes would be possible for their child with blood type A?

1. IAi
2. IAIA
3. IBIB
4. IAIB

SC 7. Which of the following rows indicates the relationship between the IA and IB alleles and the relationship between the IA and i alleles for the blood type gene?

 

Row	Relationship between IA and IB	Relationship between IA and i
A.	co-dominant	co-dominant
B.	co-dominant	dominant-recessive
C.	dominant-recessive	co-dominant
D.	dominant-recessive	dominant-recessive

 

SC 8. A dominant allele, XE, carried on the X chromosome, causes the formation of faulty tooth enamel; the resulting enamel being either very thin or very hard. The faulty tooth enamel trait will appear in all of the daughters but none of the sons if the children have a father with which of the following?

1. normal tooth enamel and a mother with normal tooth enamel
2. normal tooth enamel and mother with faulty tooth enamel
3. faulty tooth enamel and a mother with normal tooth enamel
4. faulty tooth enamel and a mother with faulty tooth enamel

Use the following information to answer SC 9.

 

Cat coat colour results from the interaction of three different genes. A gene for black-based colours is located on an autosomal chromosome. A gene for red-based colours is located on the X chromosome. A different gene located on a separate autosomal chromosome determines pigment density in cat hair.

 

The black based gene has three possible alleles: B-black, b-chocolate and bI-cinnamon. If pigmentation in cat hair is dense, the phenotypes listed below are possible.

 

Genotype	Phenotype
BB, Bb, BbI	Black
bb, bbI	Chocolate
bIbI	Cinnamon

 

SC 9. According to the data above, the relationship among these alleles is such that the

1. black allele is co-dominant with the chocolate and cinnamon alleles
2. black allele is co-dominant with the chocolate allele, and the chocolate allele is co-dominant with the cinnamon allele
3. black allele is dominant over the chocolate and cinnamon alleles, and the chocolate allele is dominant over the cinnamon allele
4. black allele is dominant over the chocolate and cinnamon alleles, and the chocolate and cinnamon alleles are co-dominant

 

Try This

 

TR 13. One of the essential skills in genetics is learning to apply what you know to new situations. For excellent review material, conduct a web search using the terms “biology + Arizona + edu + Mendelian genetics + problem sets + monohybrid cross.” Many of the sites available offer help or tutorial with each question. Complete the additional questions involving multiple alleles and incomplete dominance that are useful to you at this point in your studies.

 

Reflect on the Big Picture

 

In the Big Picture section, you may have wondered why some people in your family are alike and some are not. Your parents may be Type A and Type B blood. Your sister is also type A, but you are Type O. From your work in this lesson you should understand how multiple alleles can increase the variation in phenotypes in individuals.

 

Understanding blood types and their inheritance pattern can go a long way when working with family histories, developing pedigrees, and determining paternity. In Biology 20 you learned about the four phenotypes of blood and what can happen if a person receives incompatible blood. In this lesson you examined the three alleles for blood type and how they account for the four possible phenotypes. Using this information, you can predict possible blood types of future children, study family pedigrees to determine lineage, and even determine if there was a mix-up of babies in the hospital!

 

 

Module 6: Lesson 3 Assignment

 

Submit your completed Module 6: Lesson 3 Assignment to your teacher for assessment.

 

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