Mendelian Genetics.
Chapter 9
VBS
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I. Mendel's experimental procedure and basic terms
- Identify Gregor Mendel in terms of his background and the
importance of his experiments.
- Give the reasons why peas might be a good organism for studying
genetics.
- Define major terms related to genetics as listed:
II. Mendel's
principle of segregation
- Define monohybrid cross and explain how Mendel set up his crosses
- State the principle(theory) of segregation
- Show using Punnett Squares the results when the F1's are crossed.
Fig 9.8
- Give the expected genotype and phenotype ratios for the
Monohybrid cross.
- Explain the role of test crosses in confirming Mendel's theory of
segregation.
- Explain the relationship between Mendel's theory and what happens
to chromosomes during meiosis.
Comment: Recall that in diploid organisms chromosomes come in pairs.
Since genes are on chromosomes, genes must come in pairs! And when
gametes form during meiosis each gamete gets one chromosome from each
pair but not both. In other words, the chromosomes segregate into
different gametes. When Mendel was investigating genetics, the
connection between chromosomes and genes was unknown and was not
discovered until the early party of the 20th century.
Mendel also conducted test crosses to test his principle of
segregation. In a test cross an organism showing the dominant phenotype
is mated with a homozygous recessive individual and the offspring
examined. If the parent with the dominant phenotype is homozygous
dominant then all the offspring will show the dominant phenotype. If
the parent with the dominant phenotype is heterozygous then half the
offspring will be heterozygous and show the dominant phenotype and the
other half of the offspring will show the recessive phenotype. See page
149 for a discussion of test crosses and figure 9.12
III. Principle
of independent assortment
- Explain Mendel's procedure for doing a dihybrid
cross
- Set up and use the Punnett Square for dihybrid cross problems.
See Figure 9.10
- State Mendel's theory of Independent
Assortment
- Explain how to do dihybrid crosses using the multiplication
rule for independent probabilities(See page 149-150)
- Analyse simple pedigrees as shown on p 151
- Define the word autosome (as opposed to sex chromosome)as it
relates to chromosomes.
Comment. The multiplication technique is a powerful technique for
handling genetics problems. It is much quicker than Punnett Squares and
can be applied to almost any situation in genetics no matter how
complex the cross!
IV Dominance relations and other patterns of single gene
inheritance.
- Give examples of
codominance and
incomplete dominance
- Explain the distinction between codominance and incomplete
dominance p 155 -156
- Explain the inheritance of the alleles involved in the ABO blood
system Fig 9.20
- Explain X linkage and explain the mode of inheritance for
color blindness and hemophilia p 181
V. Multiple effects of single genes and many genes affecting a
single trait p 157-158
- Define pleiotropy
- Identify the cause of sickle cell anemia
- Explain why sickle cell anemia is a pleiotropic trait Fig 9.21
- Explain polygenic inheritance.
- Discuss the role of environment in determining the phenotype.
Comment. Genes and environment can interact in complex ways. As noted
in your text, some traits are influenced mainly by genetics other
traits are influenced by environment and many traits are influenced by
both!
VI. Chromosomal basis of inheritance.
- State the chromosomal theory of inheritance
- Identify what phases of meiosis are related to Mendels two
principles. See Fig 9.23
- Define gene linkage.
- Explain how crossing over leads to recombinant chromosomes and
phenotypes.
- Compare the expected results for a test cross if two loci
are linked vs if they are not linked.
VII. Sex chromosomes and sex linked genes.
Explain the basic mechanism of sex determination in people
Explain the significance of the SRY gene on the Y chromosome.
Comment: we know that other genes influence biological sex. One's
gender as opposed to biological sex may be influenced by genetics and
environment in complex ways that are poorly understood.
Solve simple problems related to sex linkage and give examples of sex
linked traits in humans.
Comments: There is nothing sacred about the sex determining mechanism
in humans. In both fruit flies and humans females are XX and males are
XY but in birds, the females are XY and the males are XX! In still
other organisms biological sex is due to environment and in some
species such as the clown fish of Nemo fame adult fish can change
genders! Other organisms such as earthworms have both male and female
reproductive parts functional at the same time.
Explain how the Y chromosome can be used to study human evolution. Even
in humans we know that other genes influence biological sex and one's
gender as opposed to biological sex may be influenced by genetics and
environment in complex ways that are poorly understood.