Biology Commonwealth of Virginia

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Resources
Name: Date
Activity
Answer Key — Sex-linked Chromosomes
Flow Chart for DNA Replication, mRNA Transcription, and Translation

Sample assessment

Have students take an online assessment in Mendel’s Laws and Punnett squares at http://www.borg.com/~lubehawk/mendel.htm#reminder. Have them look for vocabulary review questions.

Follow-up/extension

Have students add another generation to the pedigree, using F2, ♂4 or F2, ♀1. Design the Punnett square first, and then add male/female and offspring in the area below F2.
Have students develop a pedigree, using personal family data. Some traits that are easily followed are diabetes, sickle-cell anemia, eye color, and certain cancers. Use same materials as found in the lesson “DNA Replication, mRNA Transcription, and Translation.”

Resources

Suggested Web sites with information on Punnett squares and Mendelian genetics:
Lubey, Steve. “Mendel’s Genetic Laws.” Lubey’s Biohelp! http://www.borg.com/~lubehawk/mendel.htm.
Monohybrid Crosses. http://www.athro.com/evo/gen/punexam.html#monohybrid.

Suggested Web sites with information on sex-linked characteristics and meiosis:

Genetics, Inheritance & Variation. http://www.biologymad.com/master.html?http://www.biologymad.com/GeneticsInheritance/geneticsinheritance.htm.
Linked and Sex-Linked Genes. http://biology.clc.uc.edu/courses/bio105/sex-link.htm.
Sex-Linked Inheritance. http://www.uic.edu/nursing/genetics/Lecture/Types/SingleGene/Sex-linked/sexlinked.htm.

Sex-Linked Chromosomes

Student Activity Sheet

Name: Date:

Activity 1. Sex-Linked Chromosomes and Inheritance

Background

Watch the animated tutorials at http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/main.html.

Review the phases of meiosis I and meiosis II, and then answer the following questions.

1. Where does meiosis take place?

2. How many chromosomes are in the cells in the beginning of meiosis I? _____

3. How many chromosomes are there in the cells at the end of meiosis I? _____

4. How many chromosomes are there in the cells at the end of meiosis II? _____

		♂ gametes
		X	Y
♀ gametes	X	1	2
♀ gametes	X	3	4

Watch http://www.borg.com/~lubehawk/psquare.htm about the Punnett square. A monohybrid cross will show the inheritance of the X and Y chromosomes (♀ = female; ♂ = male). Fill in the Punnett square shown at right.

5. Females always contribute a(n) ______chromosome.

6. Males contribute a(n) ______ or ______chromosome.

7. Of the four possible offspring, how many are females (♀)? _____

How many are males (♂)? _____

8. The probability of the offspring being a female is _____:_____.

9. The probability of the offspring being a male is _____:_____.

Activity

A well-known example of a sex-linked, or X-linked, characteristic is color blindness in humans. While 8 percent of all males are color blind, only 0.7 percent of females have this characteristic. The genes for green-sensitive and red-sensitive rhodopsin are on the X chromosome. It is a recessive gene that is only expressed in homozygous females, X^r X^r , or males who have inherited the recessive gene from their mothers, X^rY.

1. Normal male; Normal female ♀ = female ♂ = male R = Dominant allele r = recessive allele			♂ gametes
			X^R	Y
	♀ gametes	X^R	1	2
		X^R	3	4
F1 Genotype
F1 Phenotype (color-blind female, normal female, color-blind male, normal male, carrier female)

The following five Punnett squares show crosses involving color blindness with normal females and males, carrier females, and color-blind females and males. The symbols X^R for the dominant allele (normal rhodopsin, normal vision) and X^r for the recessive allele (nonfunctional rhodopsin, color-blind vision) are used.

Fill in each of the following five Punnett squares.

2. Normal male; Carrier female ♀ = female ♂ = male R = Dominant allele r = recessive allele			♂ gametes
			X^R	Y
	♀ gametes	X^R	1	2
		X^r	3	4
F1 Genotype
F1 Phenotype

3. Normal male; Color-blind female ♀ = female ♂ = male R = Dominant allele r = recessive allele			♂ gametes
			X^R	Y
	♀ gametes	X^r	1	2
		X^r	3	4
F1 Genotype
F1 Phenotype

4. Color-blind male; Carrier female ♀ = female ♂ = male R = Dominant allele r = recessive allele			♂ gametes
			X^r	Y
	♀ gametes	X^R	1	2
		X^r	3	4
F1 Genotype
F1 Phenotype

5. Color-blind male; Normal female ♀ = female ♂ = male R = Dominant allele r = recessive allele			♂ gametes
			X^r	Y
	♀ gametes	X^R	1	2
		X^R	3	4
F1 Genotype
F1 Phenotype

After completing the Punnett squares above, use the information for the Pedigrees activity on the following page.

Activity 2. Pedigrees

Dogs, cats, and horses often have pedigrees. Pedigrees can be done for humans, too. Use the information from the Punnett squares above to fill in the following red-green color-blindness pedigree chart.

Square 2. Square 3.

Use coloring/shading to indicate the characteristics of each person, according to the following key:

♂

Normal female Normal male

♂

Color-blind female Color-blind male

Carrier female

10. How many males are affected by red-green color blindness? _____

11. How many females are affected by red-green color blindness? _____

12. How many females are carriers of the red-green color blindness gene? _____

13. What is the genotype of F1, Family 2, ♂4? __________

14. Which Punnett square is represented by the star? ______________________________

15. Where did F2, ♀1 get the gene for red-green color blindness? _____________________

Extension Activity

Add another generation using F2, ♂4 or F2, ♀1. Design the Punnett square first, and then add male/female and offspring in the area below F2.

Answer Key — Sex-linked Chromosomes

Review meiosis with students. Then, have them watch the animated tutorials. Emphasize that meiosis occurs only in gametes — the egg and sperm cells. Stress that after meiosis in humans, the chromosome number is now 23 instead of the 46 chromosomes in somatic cells. Have students answer the questions below.

1. Where does meiosis take place? Sex cell in the ovaries and testes, which produce eggs and sperm, respectively.

2. How many chromosomes are in the cells at the beginning of meiosis I? diploid

3. How many chromosomes are in the cells at the end of meiosis I? haploid

4. How many chromosomes are in the cells at the end of meiosis II? haploid

♂ gametes

X

Y

♀ gametes

X

XX
1

XY
2

X

XX

3

XY
4

Have students watch http://www.borg.com/~lubehawk/psquare.htm about the Punnett square. Use Lubey’s explanation and practice page for an introduction or a review. Introduce sex-linked genes. Explain how Punnett squares work for sex-linked chromosomes. Have students fill in the Punnett square shown at right.

5. Females always contribute a(n) X chromosome.

6. Males contribute a(n) X or Y chromosome.

7. Of the four possible offspring, how many are females (♀)? 2

How many are males (♂)? 2

8. The probability of the offspring being a female is 1:2.

9. The probability of the offspring being a male is 1:2.

1. Normal male Normal female ♀ = female ♂ = male R = Dominant allele r = recessive allele			♂ gametes
			X^R	Y
	♀ gametes	X^R	X^RX^R 1	X^RY 2
		X^R	X^RX^R 3	X^RY 4
F1 Genotype	2X^RX^R, 2X^RY
F1 Phenotype	2 normal females, 2 normal males

2. Normal male Carrier female ♀ = female ♂ = male R = Dominant allele r = recessive allele			♂ gametes
			X^R	Y
	♀ gametes	X^R	X^RX^R 1	X^RY 2
		X^r	X^RX^r 3	X^rY 4
F1 Genotype	1X^RX^R, 1X^RX^r, 1X^RY, 1X^rY
F1 Phenotype	1 normal female, 1 carrier female, 1 normal male, 1 color-blind male

3. Normal male Color-blind female ♀ = female ♂ = male R = Dominant allele r = recessive allele			♂ gametes
			X^R	Y
	♀ gametes	X^r	X^RX^r 1	X^rY 2
		X^r	X^RX^r 3	X^rY 4
F1 Genotype	2X^RX^r, 2X^rY
F1 Phenotype	2 carrier females, 2 color-blind males

4. Color-blind male Carrier female ♀ = female ♂ = male R = Dominant allele r = recessive allele			♂ gametes
			X^r	Y
	♀ gametes	X^R	X^RX^r 1	X^RY 2
		X^r	X^rX^r 3	X^rY 4
F1 Genotype	1 X^RX^r, 1 X^rX^r 1X^RY, 1X^rY
F1 Phenotype	1 carrier female, 1 color-blind female 1 normal male, 1 color-blind male

5. Color-blind male Normal female ♀ = female ♂ = male R = Dominant allele r = recessive allele			♂ gametes
			X^r	Y
	♀ gametes	X^R	X^RX^r 1	X^RY 2
		X^R	X^RX^r 3	X^RY 4
F1 Genotype	2 X^RX^r 2 X^RY
F1 Phenotype	2 carrier females 2 normal males

Square 2. Square 3.

10. How many males are affected by red-green color blindness? 5

11. How many females are affected by red-green color blindness? 1

12. How many females are carriers of the red-green color blindness gene? 6

13. What is the genotype of F1, Family 2, ♂4? X^r Y

14. Which Punnett square is represented by the star? Normal male, color-blind female

15. Where did F2, ♀1 get the gene for red-green color blindness? From her father

Flow Chart for DNA Replication, mRNA Transcription, and Translation

Organizing Topic Genetics

Overview Students create flow charts demonstrating the sequence of events in DNA replication, in mRNA transcription, and in translation. The flow charts receive peer evaluation by at least one other group and are assessed for accuracy by the teacher. The lesson is typically used as an in-class activity to review these concepts or as an informal assessment during a unit on DNA structure and function.

Related Standards of Learning BIO.6 f, g

Directory: testing -> sol -> scope sequence
scope sequence -> History and Social Science Standards of Learning Enhanced Scope and Sequence
sol -> Strand Earth Patterns, Cycles, and Change Topic Investigating fossils in sedimentary rock Primary sol
testing -> Prairie State Achievement Exam
testing -> Testing and Assessment updated Tentative schedules
testing -> Local unit tests Located at module-name
sol -> P. O. Box 2120 Richmond, Virginia 23218-2120
sol -> Strand Interrelationships in Earth/Space Systems Topic Investigating ocean currents Primary sol
sol -> History and Social Science Standards of Learning for Virginia Public Schools Wo Board of Education Commonwealth of Virginia March 2015 History and Social Science Standards of Learning for Virginia Public Schools Adopted in March 2015 by the Board of

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