Essential Biology 4.1/4.2 Chromosomes, Genes, Alleles,
Mutations/Meiosis
Due Date:
Student Name:
Resources: Clegg pp. 91-94, 98-102 and Revision Guide pp. 23 covering Topic 4.1 .(and some review of
transcription and translation!)
1. Define the following:
Chromosome
Gene
Allele
Gene locus
Genome
Chromatid
Mutation
Haploid
Diploid
2. State the components of a chromosome.
 DNA &
3. State the number of chromosomes present in a single human diploid cell.
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4. Identify structures a. and b. on the line drawing of a chromosome in
prophase shown to the right.
a.
b.
5. Give two examples of genes and some of their possible alleles.
Gene
Eye colour
Possible alleles
Blue, brown, green, hazel
6. List factors that increase the chance of a genetic mutation.
 UV
 chemical carcinogen (tar in tobacco)

certain organic solvents
 uncorrected mistakes in natural replication
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Essential Biology 4.1/4.2 Chromosomes, Genes, Alleles,
Mutations/Meiosis
Due Date:
Student Name:
7. Compare the following types of base-substitution mutation.
Silent mutation
Number of bases
substituted
Mis-sense mutation
1
Stop codon produced
early – polypeptide
shortened
Effect on polypeptide
Example illness
Nonsense mutation
Sickle cell disease
Resources: Clegg pp. 94-97
8. Define homologous chromosomes.
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9. Explain reduction division.
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10. State the function of meiosis.
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11. Add chromosomes and annotate the diagram below summarizing the steps in meiosis.
Identify the stage where crossing over occurs and state its effect.
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Essential Biology 4.1/4.2 Chromosomes, Genes, Alleles,
Mutations/Meiosis
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Essential Biology 4.1/4.2 Chromosomes, Genes, Alleles,
Mutations/Meiosis
Due Date:
Student Name:
12. Compare mitosis and meiosis:
Mitosis
Meiosis
Number of divisions
Number of daughter cells
Chromosome number in
daughter cells
Functions:
13. Outline the major events and movements of chromosomes occurring at these stages of meiosis:
Meiosis I
Meiosis II
Interphase
Interphase
Prophase I
Prophase II
Metaphase I
Metaphase II
Anaphase I
Anaphase II
Telophase I
Telophase II
Cytokinesis
Cytokinesis
No replication occurs in interphase
between Meiosis I and II.
14. Deduce the answers to these questions.
a. A cell with a diploid number of 12 chromosomes goes through meiosis. How many daughter
cells will be produced and with how many chromosomes in each?
 Cells:
 Chromosomes:
b. A gamete contains 18 chromosomes. How many chromosomes in the somatic cell?

Chromosomes:
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Essential Biology 4.1/4.2 Chromosomes, Genes, Alleles,
Mutations/Meiosis
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c. A diploid cell with 16 chromosomes undergoes meiosis. How many chromatids are present in
metaphase I?

Chromatids:
15. A cell with a chromosome number (n) of 3 undergoes meiosis. Draw a series of diagrams to
outline the steps of meiosis.
16. Describe what you can see in this image.
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17. Distinguish between chromosomes, sister chromatids and
bivalents.
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Essential Biology 4.1/4.2 Chromosomes, Genes, Alleles,
Mutations/Meiosis
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18. Annotate the diagram below to show what happens in non-disjunction in meiosis II.
19. Describe how non-disjunction and fertilization lead to trisomy.
 Non-disjunction:
 Fertilization:
20. Distinguish between non-disjunction and trisomy.
 Non-disjunction:
 Trisomy:
QUESTIONS 21-27 WILL BE COMPLETED IN CLASS!
21. Compare the outcomes of non-disjunction in anaphase I with anaphase II:
Non-disjunction in…
Number of normal cells
Cells with extra chromosome (n+1)
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Anaphase I
Anaphase II
Essential Biology 4.1/4.2 Chromosomes, Genes, Alleles,
Mutations/Meiosis
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Cells with chromosome missing (n-1)
22. Using information in the graph, outline the effect of maternal age on likelihood of Down
Syndrome:
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23. Describe the effects of Down syndrome.
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24. Compare the outcomes of non-disjunction in anaphase I with anaphase II:
Non-disjunction in…
Number of normal cells
Cells with extra chromosome (n+1)
Cells with chromosome missing (n-1)
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Anaphase I
Anaphase II
Essential Biology 4.1/4.2 Chromosomes, Genes, Alleles,
Mutations/Meiosis
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25. A karyotype can be used to test for non-disjunction disorders. Fetal cells are taken and the
number of chromosomes counted. Outline how these cells are retrieved:
Chorionic Villus Sampling (CVS):


Amniocentesis:

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26. State three visual aspects of homologous chromosomes which can be used to identify them for
the purpose of a karyotype?
a. Banding patterns
b.
c.
d.
27. Analyse this karyotype:
Gender:
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Essential Biology 4.1/4.2 Chromosomes, Genes, Alleles,
Mutations/Meiosis
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Essential Biology 4.1/4.2 Chromosomes, Genes, Alleles,
Mutations/Meiosis
Due Date:
Student Name:
28. Describe the effects of sickle cell disease on sufferers in terms of:
a. Hemoglobin production

b. Symptoms and mortality
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29. Identify parts of the world where a single sickle cell (Hbs) allele could be beneficial

Explain your answer
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30. Define evolution.
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31. Outline how mutations lead to evolution by natural selection.
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32. Outline how the spread of the sickle cell gene is an example of natural selection in action.
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33. How could this be an example of a correlation which has a strong element of causality?
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Essential Biology 4.1/4.2 Chromosomes, Genes, Alleles,
Mutations/Meiosis
Due Date:
Student Name:
In-class activity: Using gene databases
(ICT Databases)
1. Using the NCBI gene database at http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene ,
identify the gene locus of the HBB (hemoglobin) gene.

2. Using the same database, look for the gene related to the illness PKU (phenylketonuria)
a. What is the gene name?

b. What is the gene locus of this gene?

c. Which enzyme is encoded by this gene?

d. What is the consequence of a base-substitution (mis-sense) mutation of this gene?
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e. How is PKU diagnosed and why must it be diagnosed as early as possible?
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3. Stem cells link:
Read this article: http://notexactlyrocketscience.wordpress.com/2007/12/08/sickle-cell-micecured-by-stem-cells-reprogrammed-from-their-own-tails/
a. What is an IPS stem cell?
b. Outline the use of this technology in treating the mice with sickle cell disease.
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