Download Checklist unit 15: The Chromosomal Basis of Inheritance

BIOLOGY SEMESTER ONE
UNIT 15
CHECKLIST UNIT 15: THE CHROMOSOMAL BASIS OF INHERITANCE
In this module, you will explore how the arrangement of genes on a chromosome can affect the
way the genes are inherited: For genes located on the same chromosome, those further apart
from each other have a higher probability of being sorted independently than genes that are in
close proximity of each other (which will, more often than not, be sorted together). The latter
are referred to as “linked genes.” Genes found on sex chromosomes have altered inheritance
patterns because the paired sex chromosomes, XY, are not homologous in males (in mammals).
This can lead to higher incidents in males of certain traits associated with the X chromosome,
including colour blindness and haemophilia. It can also be responsible for less severe
consequences, like the tortoiseshell colouration in some female cats.
In addition, you will also discover what happens when there are errors in chromosome
separation and interaction during meiosis: If chromosomes do not separate completely, the
resulting gamete-cell may include extra copies of certain chromosomes, and deletions of
others. Though this may result in the death of the fertilized egg, some of these errors can
produce offspring with specific, identified disorders such as Down Syndrome or Kleinfelter’s.
LEARNING OBJECTIVES
At the end of this module you should be able to:
1. Explain how the observations of cytologists and geneticists provided the basis for the
chromosome theory of inheritance.
2. Describe how sex is genetically determined in humans and in other types of organisms.
3. Discuss inheritance patterns of sex-linked genes, and explain why certain diseases are more
common in human males.
4. Describe the process of X inactivation in female mammals. Explain how this phenomenon
produces the tortoiseshell colouration in cats.
5. Distinguish between linked, unlinked, and sex-linked genes.
6. Describe the independent assortment of chromosomes during Meiosis I. Explain how
independent assortment of chromosomes produces genetic recombination of unlinked
genes, and explain why linked genes do not assort independently. Explain how crossing
over can unlink genes.
7. Explain how nondisjunction can lead to aneuploidy, and understand trisomy and
polyploidy. Explain how these major chromosomal changes occur and describe possible
consequences.
8. Distinguish among deletions, duplications, inversions, and translocations, and discuss
effects.
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BIOLOGY SEMESTER ONE
UNIT 15
CHECK LIST
 Read Chapter 15: The Chromosomal Basis of Inheritance, of Campbell and Reece’s
Biology, 8th Ed.
 As you are reading, address each of the learning objectives listed above.
 Consider making flash cards for the terminology list provided. This will be beneficial for
studying for the midterm and final exams later in the semester.
 You may be able to review the PowerPoint Lecture and other resources for this unit.
Refer to your instructor’s notes for more details.
 Complete the “Mendel 2 Worksheet: Sex Linked Traits”.
 For extra practice, try the Self Quiz or Practice Test on the Mastering Biology Website.
To log onto the website, use the access code provided in your textbook. You will also
find other resources, such as downloadable MP3 tutorials for each chapter, a glossary,
and an electronic copy of your text—you can catch up on your reading anywhere!
KEY TERMS
aneuploidy
Barr body
dendrite
duplication
genetic map
genetic recombination
genomic imprinting
inversion
linked genes
monosomic
nondisjunction
parental type
polyploidy
sex-linked gene
translocation
trisomic
wild type
ROOT WORDS TO KNOW1
aneu- = without (aneuploidy: a chromosomal aberration in which certain chromosomes are
present in extra copies or are deficient in number)
cyto- = cell (cytogenetic maps: charts of chromosomes that locate genes with respect to
chromosomal features)
hemo- = blood (hemophilia: a human genetic disease caused by a sex-linked recessive allele,
characterized by excessive bleeding following injury)
mono- = one (monosomic: a chromosomal condition in which a particular cell has only one copy
of a chromosome, instead of the normal two; the cell is said to be monosomic for that
chromosome)
1
(Pearson Education, 2010)
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BIOLOGY SEMESTER ONE
UNIT 15
non- = not; dis- = separate (nondisjunction: an accident of meiosis or mitosis in which both
members of a pair of homologous chromosomes or both sister chromatids fail to move apart
properly)
poly- = many (polyploidy: a chromosomal alteration in which the organism possesses more than
two complete chromosome sets)
re- = again; com- = together; bin- = two at a time (recombinant: an offspring whose phenotype
differs from that of the parents)
trans- = across (translocation: attachment of a chromosomal fragment to a nonhomologous
chromosome)
tri- = three; soma- = body (trisomic: a chromosomal condition in which a particular cell has an
extra copy of one chromosome, instead of the normal two; the cell is said to be trisomic for
that chromosome)
SOME USEFUL RESOURCES
Linked and Sex Linked Genes- a good set of examples and explanations can be found at:
http://biology.clc.uc.edu/Courses/bio105/sex-link.htm
SOURCES
Campbell, N. A. (2008). Biology, Eighth Edition. San Francisco: Pearson, Benjamin Cummings.
Pearson Education. (2010). Retrieved 2010, from Mastering Biology : http://session.masteringbiology.com
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BIOLOGY SEMESTER ONE
UNIT 15
NANSLO Biology Core Units and Laboratory Experiments
by the North American Network of Science Labs Online,
a collaboration between WICHE, CCCS, and BCcampus
is licensed under a Creative Commons Attribution 3.0 Unported License;
based on a work at rwsl.nic.bc.ca.
Funded by a grant from EDUCAUSE through the Next Generation Learning Challenges.
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