Download Checklist unit 14: Mendel and the gene idea

BIOLOGY SEMESTER ONE
UNIT 14
CHECKLIST UNIT 14: MENDEL AND THE GENE IDEA
In this module you will investigate how genes are inherited or passed along to offspring.
Mendel’s model of inheritance is based on the idea that genes are inherited in discrete
packages form parents and were not “blended” as previously thought. Mendel crossed white
flower and purple flower plants, and discovered the result was not a blend, but instead all
purple flowered. He then considered the idea of heredity units, which he called "factors,” one
of which is a recessive characteristic and the other dominant. Mendel said that factors (we now
call them genes) normally occur in pairs in ordinary body cells, yet segregate during the
formation of sex cells. Each member of the pair becomes part of the separate sex cell. The
dominant gene, such as the purple flower in Mendel's plants, will hide the recessive gene, the
white flower. After, he correctly theorized that genes can be paired in three different ways for
each trait: AA, aa, and Aa. The capital "A" represents the dominant factor and lowercase "a"
represents the recessive.
Mendel stated that each individual has two factors (genes) for each trait, one from each parent.
The two genes may or may not contain the same information. If the two genes for a trait are
identical, the individual is called homozygous for that trait. If the two genes have different
information, the individual is called heterozygous with regards to that trait. The different
possible forms of a gene are called alleles. The genotype of an individual is made up of the
many alleles it possesses.
An individual's physical appearance, or phenotype, is determined by its alleles as well as by its
environment. An individual possesses two alleles for each trait; one allele is given by the female
parent and the other by the male parent. They are passed on when an individual matures and
produces gametes: egg and sperm. When gametes form through meiosis, the paired alleles
separate randomly so that each gamete receives a copy of one of the two alleles. The presence
of an allele doesn't promise that the trait will be expressed in the individual that possesses it.
In heterozygous individuals the only allele that is expressed is the dominant. The recessive
allele is present but its expression is hidden.
Mendel summarized his findings in two laws; the Law of Segregation and the Law of
Independent Assortment. Mendel's findings allowed other scientists to predict the expression
of traits on the basis of mathematical probabilities. In this module you will be introduced to
Punnett Squares, which will aid you in finding probabilities for genetic expression when
performing a test cross.
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BIOLOGY SEMESTER ONE
UNIT 14
LEARNING OBJECTIVES
At the end of this module you should be able to do the following:
1. Understand and use the terminology related to Mendelian genetics.
2. Identify and explain the four components of Mendel’s segregation model of genetic
inheritance.
3. Create and use Punnett squares to predict the outcomes of various crosses.
4. Understand and apply the laws of probability (multiplication & addition rules) to Mendelian
inheritance.
5. Discuss Mendel’s laws of segregation and independent assortment and relate them to
meiosis.
6. Discuss various forms of genetic dominance (eg: complete / incomplete / codominant /
recessive) and how they may apply to phenotype.
7. Explain why dominant alleles are not necessarily more common in a population.
8. Discuss gene interaction (eg: epistasis) and environmental influence on phenotype.
9. Discuss how alleles arise and are maintained in populations, even when they appear to be
non-beneficial or even harmful.
CHECK LIST
 Read Chapter 14 of Campbell and Reece’s Biology, 9th Ed.
 As you are reading, address each of the learning objectives listed above.
 We recommend that you make 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 Worksheet”. The Mastering Biology website has some extra
tutorials on working through Punnett Squares and probabilities. They can be found in
the student area by highlighting Chapter 14 in the top drop down menu and clicking
“go.” Here you will find activities on monohybrid and dihybrid crosses, as well as the
Gregor’s Garden activity. These may be helpful practice.
 Watch the video clip “Novelty Gene.” Post a response to the discussion board
discussing which you feel contributes most strongly to a specific behaviour of your own:
genetics or the environment? Give specific evidence to back up your claim. Read and
comment on 2 of your fellow classmates’ posts.
 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
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BIOLOGY SEMESTER ONE
UNIT 14
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
carrier
character
codominance
complete dominance
dihybrid
dominant allele
epistasis
F1 generation
F2 generation
ROOT WORDS TO KNOW
heterozygous
homozygous
hybridization
incomplete dominance
law of independent
assortment
law of segregation
monohybrid
P generation
pedigree
phenotype
pleiotropy
polygenic inheritance
Punnett square
recessive allele
test cross
trait
true-breeding
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-centesis = a puncture (amniocentesis: a technique for determining genetic abnormalities in a
fetus by the presence of certain chemicals or defective fetal cells in the amniotic fluid, obtained
by aspiration from a needle inserted into the uterus)
co- = together (codominance: phenotype in which both dominant alleles are expressed in the
heterozygote)
di- = two (dihybrid cross: a breeding experiment in which offspring of a cross of parental
varieties differing in two traits are mated)
epi- = beside; -stasis = standing (epistasis: a phenomenon in which one gene alters the
expression of another gene that is independently inherited)
geno- = offspring (genotype: the genetic makeup of an organism)
hetero- = different (heterozygous: having two different alleles for a trait)
homo- = alike (homozygous: having two identical alleles for a trait)
mono- = one (monohybrid cross: a breeding experiment that crosses offspring of a cross of
parental varieties differing in a single character)
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(Pearson Education, 2010)
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BIOLOGY SEMESTER ONE
UNIT 14
pedi- = a child (pedigree: a family tree describing the occurrence of heritable characters in
parents and offspring across as many generations as possible)
pheno- = appear (phenotype: the physical and physiological traits of an organism)
pleio- = more (pleiotropy: when a single gene impacts more than one characteristic)
poly- = many; gene- = produce (polygenic: an additive effect of two or more gene loci on a
single phenotypic character)
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
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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