Module 6

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

Reflect and Connect

 

This lesson has helped you to understand how to track two traits at the same time, while still following all of the inheritance patterns you have already learned. Complete the following Self-Check to apply all of the principles that you have been mastering. 

 

Self-Check

 

In tomato plants, purple stems (P) are dominant to green stems (p), and red tomatoes (T) are dominant to yellow tomatoes (t). The two genes are located on separate chromosomes.

 

A purple-stemmed, red-tomato plant is crossed with a purple-stemmed, yellow-tomato plant. They produce the following:

• 28 purple-stemmed, red-tomato plants
• 31 purple-stemmed, yellow-tomato plants
• 11 green-stemmed, red-tomato plants
• 9 green-stemmed, yellow-tomato plants

SC 6. The genetic compositions of the parents are as follows:

1. PpTt and PPTT
2. PPTt and PpTT
3. PpTt and PpTt
4. PpTt and Pptt

SC 7. One of the green-stemmed, red-tomato plants was crossed with another tomato plant. One of the offspring was a purple-stemmed, yellow-tomato plant. If this offspring were crossed with a green-stemmed, yellow-tomato plant, then the possible phenotype(s) of the offspring would be as follows:

1. green-stemmed, yellow-tomato plants
2. green-stemmed, yellow-tomato plants and purple-stemmed, yellow-tomato plants
3. green-stemmed, yellow-tomato plants; purple-stemmed, yellow-tomato plants; and purple-stemmed, red-tomato plants
4. green-stemmed, yellow-tomato plants; purple-stemmed, yellow-tomato plants; purple-stemmed, red-tomato plants; and green-stemmed, red-tomato plants

Use the following information to answer SC 8.

 

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, or s–wrinkled, and seed coat colour can be represented as Y–yellow, or 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 seeds
  

Numerical Response

 

SC 8. What would the F2 seed phenotype ratio that Mendel obtained upon crossing two heterozygous smooth, yellow F1 individuals have been? List the ratio in the following order:

smooth green : wrinkled green : smooth yellow : wrinkled yellow.

 

Use the following additional information to answer SC 9.

 

Mendel selected two varieties of pea plants from seeds he had grown. One variety of peas came from a field planted with smooth, yellow seeds. Another variety of peas came from a field planted with wrinkled, green seeds. These two varieties of peas were crossed to produce the following:

• 255 plants with smooth, green seeds
• 268 plants with wrinkled. green seeds
• 237 plants with smooth, yellow seeds
• 240 plants with wrinkled, yellow seeds

From the phenotype ratio of the offspring, Mendel deduced that the smooth and yellow parents had the genotype YySs.

SC 9. This type of cross is referred to as which of the following:

1. test cross
2. monohybrid cross
3. homozygous cross
4. heterozygous cross

Use the following information to answer SC 10.

 

In pea plants, tall (T) is dominant over short (t), and round seed (R) is dominant over wrinkled seed (r). The Punnett square below shows a cross between a heterozygous, tall–heterozygous, round-seed pea plant and a short–heterozygous, round-seed pea plant. Different types of offspring are represented by numbers.

 

	TR	Tr	tR	tr
tR	1	2	3	4
tr	5	6	7	8

 

SC 10. Which two types of offspring are pure breeders for both plant height and seed shape?

1. 1 and 6
2. 2 and 5
3. 3 and 8
4. 4 and 7

 

Reflect on the Big Picture

 

In the Big Picture you wondered why you have your mother’s eyes but not her nearsightedness. What might cause certain traits to be inherited not others?

 

In this lesson, you learned to work with more than one gene. This allows you to be more efficient when working with inheritance problems. By working with more than one gene, you are able to see how traits on different chromosomes assort independently when creating gametes. Because these traits are on different chromosomes, like the figures on the different puzzle pieces of the picture, they have no effect on each other when being passed on to the next generation. For example, pea shape does not move with pea colour, and shape doesn’t affect colour. You have the gene for your mother’s eye colour because you inherited that chromosome from her egg, but the chromosome with the gene for nearsightedness did not become part of the egg from which you developed. These chromosomes assorted independently.

 

How would traits be passed on to the next generation if they were on the same chromosome? How would the movement of these figures be different now that the puzzle pieces are together? Mendel did not study such traits, but in later lessons, you will look at traits that tend to move together because they are on the same chromosome.

 

Module 6: Lesson 4 Assignment

 

Before you complete your assignment for Lesson 4, you may wish to complete Lesson 5, which examines how to calculate probability. Some of the questions in the Lesson 4 assignment require that you complete probability calculations.

When complete, submit your completed Module 6: Lesson 4 Assignment to your teacher for assessment.

 

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