Download BIO 309F Exam I Comments, thoughts, reviews, tips

BIO 309F Exam I Comments, thoughts, reviews, tips
Exam I is in class on Tuesday, 2/20. The exam will be designed to last less than the hour
and fifteen minutes allotted, probably about 50 multiple choice questions. We’ve been
told the exam can cover ~80% material from the lecture, 20% material from the textbook.
Studying consists of 4 major steps:
 Taking Careful notes during class
o This gives you an idea of what Dr. Sanders feels is and isn’t important
 Understanding all the CONCEPTS discussed in class
o There shouldn’t be a line in your notes that doesn’t make sense to you.
Not only should you understand the sentence, you should understand the
ideas behind it. For example, we talked in class on 2/13 about nondisjunction in meiosis and we also talked about Down’s syndrome…do
you understand how non-disjunction in meiosis can lead to Down’s
syndrome? Or monosomy in another chromosome?
 Memorizing all the CONCEPTS and VOCABULARY and FACTS given in class
o There’s a lot of ‘em, and you’re responsible for knowing what to
memorize and committing it to memory
 Performing well on the exam
o This involves remembering what you memorized, as well as critical
thinking (taking what you memorized and applying it to a new situation)
o Some questions involves remembering vocabulary or facts given in class
 Vocabulary memorixation question:
5. An allele is ___.
A. one of the bases in DNA
B. an alternate form of a gene
C. another term for epistasis
D. present only in males and is responsible for sex
determination
E. found in mitochondria but not in nuclei
8. The fundamental Mendelian process which involves the
separation of contrasting genetic elements at the same locus would
be called ___.
A. separation of alleles
B. independent assortment
C. continuous variation
D. discontinuous variation
E. dominance or recessiveness
 Fact memorization questions:
48. Major risk factor(s) in having a Down Syndrome child is/are:
A.
delaying having children until female is older
B.
chromosome 21 reciprocal translocation
C.
chromosome 21 mosaic
D. A and B are correct
E. A, B, and C are correct
o Some questions involve critical thinking: taking information you were
given in class and being asked about it in a way different than the way it
was given
 Example:
4.
Consider a species with a diploid (2n) number of 16
chromosomes. How many chromosomes would be found in
a trisomic somatic cell?
A. 8
B. 9
C. 16
D. 17
E. 24
 In this question, we are used to thinking about humans
only, which have a diploid (2n) number of 46. A trisomic
human has 47 chromosomes. This questions tests to see if
you understand the general concepts of diploidy and
trisomy as applied to non-humans. Applying the same
logic to non-humans tells you that a trisomic individual of
this species has 1 extra chromosome, leading to a total of
17 chromosomes.
 Another example:
6. In dihybrid crosses, the ratio 9:3:3:1 indicates ___.
A. Codominance
B. Independent assortment
C. Intermediate dominance
D. Three alleles for each trait
 This question is hard because we talked about 9:3:3:1
ratios, and we also talked about each of the concepts
mentioned in choices A – D. The trick is, do you
understand which concept a dihybrid cross illustrates? If
you do, then you’re doing above average in this class.
o 1st, you have to remember vocabulary: ‘dihybrid
cross’ was a cross with 2 different traits
o 2nd, you have to critical think and understand that
the dihybrid phenotypic ratio is 9:3:3:1, but if you
looked at each trait independently of the other, its
phenotype would give a 3:1 ratio. Combining these
2 traits is what gives the 9:3:3:1. But each trait
separately shows the same inheritrance patterns as
when you only examine 1 trait…this means that
inherited traits have nothing to do with each other,
are inherited independently, which is a result of
independent assortment. Reading through the book
section on indepdendent
assortment
and
understanding how the dihybrid cross illustrates this
would have you more prepared for this question
than simply memorizing what Dr. Sanders
mentioned during lecture for this concept.

The critical thinking questions get even harder…look at this one:
19. A man with genophobia disease marries a normal woman.
They have 8 children (4 boys and 4 girls. All of the girls have the
disease but none of the boys have the disease. How is genophobia
inherited?
A. autosomal recessive
B. Y linked
C. autosomal dominant
D. X-linked dominant
E. X-linked recessive
 This is a VERY tough problem. How can we go about
solving it? See my ‘pedigree problem solving guidelines’,
but also:
 Well, I’ve never heard of genophobia, and the ultimate
question I’m being asked is how this disease is inherited, so
I guess I wasn’t already told in class how this disease was
inherited. I suppose I’ll have to deduce the inheritance type
from the given information.
 Let’s list the given information:
o Man = disease, wife = normal
o All female offspring have disease, no male
offspring do
 Let’s use some process-of-elimination thinking: this disease
is MOST LIKELY sex-linked, because of the emphasis
placed on the gender ratios of the disease. Autosomal
diseases affect both genders equally, so this female-bias of
the disease indicates to me that this is most likely a sexlinked disease.
 There are 2 types of sex-linked, X and Y linked. If its Ylinked, ONLY MALES can EVER have the disease,
because only males have Y chromosomes. So its not Ylinked, ‘cuz females have it.
 So is it X-linked dominant or recessive? Well, we need
more
process-of-elimination,
so
we’ll
be
hypothetical…what if it is X-linked dominant?
o If it is, the mom has genotype XaXa and the dad has
genotype XAY. The punnett square resulting from
this cross would be
o In this Punnett square, all females have the disease
and all males are normal. That sounds just like
what the problem said! Let’s make sure that its not
X-linked recessive. If it was X-linked recessive, the
mom has genotype XAX_ and the dad has genotype
XaY. The only was ANY offspring can have the
disease is if the mom carries it, so she MUST be
heterozygous XAXa. The punnett square resulting
from this cross would be:
o Half of the females show the disease as do half of
the males. This COULD be what happened and
there just weren’t enough kids to see the 50:50
phenotypic ratio in both genders, but that is
unlikely. With 8 kids, all females with the disease
and no males with the disease, its MOST LIKELY
that the disease is X-linked dominant, so that’s my
answer choice.
It looks like this will be a pretty tough exam, with a good scattering of critical thinking
questions. How can I know exactly what all I need to study, and prepare properly for the
level of difficulty of questions expected on the exam? I like to re-outline my notes, in a
way that organizes ALL of the information given in class, supplements class info with
info from the book, and highlights all the FACTS and VOCABULARY that I need to
memorize. Here’s an example of how I would re-outline my notes from 2/1/2007.
To start this outline, I have my notes, the ‘outline’ Dr. Sanders handed out in class, and
my book all open. I see that this material corresponds to Ch. 3, so I open up to that
chapter. I try to follow the ‘outline’ Dr. Sanders gave in class, filling in information from
my notes and from the book for each section. My final outline looks like this.

Mendel’s experiments
o 1853
o True breeding (a plant with a trait gives rise to offspring that have the
same trait, results from self-fertilization in peas) pea plants
o Mendelian laws:
 The principle of segregation: separation of members of a gene
pair during gamete formation
 During meiotic gamete formation, each gamete gets one
allele (one of the possible alternative forms of a gene,
usually distinguished from other alleles by its phenotypic
effects) for a trait. This is what Mendel meant by the
principle of segregation.
 The principle of independent assortment: During gamete
formation, alleles of one gene pair segregate in to the gametes
independently of the alleles belonging to other gene pairs, resulting
in the production of gametes containing all possible combinations
of alleles.
 During meiosis, each gamete gets 1 copy of each
chromosome, but its random which copy the gamete might
get. You might get maternal chromosome 1 and paternal
chromosome 2, or maternal chromosome 1 and 2. Because
its random which chromosome combinations you get, its
random which allele from 1 trait will be seen in a gamete
with an allele from another trait. Because chromosomes
assort independently, alleles for different traits do also, thus
this principle.
o Mendelian inheritance: alleles for a trait are either dominant (it takes only
1 copy of the allele to see that phenotype) or recessive (it takes 2 copies of
the allele to see that phenotype)
o Monohybrid cross: (cross of 1 trait, each parent is a heterozygote)
 If T = tall and t = short, it’s a cross of tall individuals with
genotypes Tt and Tt:


Results in a 3:1 phenotypic ratio (tall:short) and 1:2:1 genotypic
ratio (homozygous tall:heterozygous tall:homozygous short)

Genotype = the specific genetic constitution of an
organism, made up of the alleles of a gene
 Phenotype = the observable properties of an organism
o Genotype vs phenotype: the phenotype is the
characteristic of a trait that you observe, the
genotype is what alleles make up the phenotype
 Test cross: (cross of 1 true-breeding and one heterozygote)
 TT x Tt OR Tt x tt
 Results in a 1:1 phenotypic and genotypic ratio
o Dihybrid cross: (cross of 2 traits, each parent is a heterozygote for both
traits)
 We’ll use tall (T) and short (t), as well as seeds that are smooth (S)
or wrinkled (s): TtSs x TtSs
 The punnett square consists of all possible allele
combinations in a gamete: TS, Ts, tS, ts
 The phenotypic and genotypic ratios:
o 9:3:3:1 phenotypic
o 1:2:1:2:4:2:1:2:1 genotypic
o Lets yse R and Y instead of T and S:
RY
Ry
rY
ry
RY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy


rY
RrYY RrYy rrYY rrYy
ry
RrYy Rryy rrYy
rryy
Non-Mendelian inheritance
o Incomplete dominance: (expression of a phenotype that is intermediate
between those of the parents
 Example: flower color
 RR = red, rr = white, Rr = pink
 In this instance, R codes for 50% red, r codes for lack of
color (white). The combinations explain the colors.
o Codominance: (full phenotypic expression of both alleles in the
heterozygote)
 In this, neither allele is dominant or recessive
 Example: blood types in humans
 AB heterozygotes carry both the A and B antigens on their
red blood cells, blood type AB
Introduction to pedigrees (a diagram listing the members and ancestral
relationships in a famil, used in the study of human heredity)
o Afflicted Males = ■, afflicted females = ●
o Non-afflicted = □, ○
More thoughts and tips
 USE YOUR TEXTBOOK!!!!!!!!!!

o The text book has the level of detail of the material you are expected to
know for the exam, whereas the lecture does not. MOST of the material
we covered in lecture also appears in your text, and you need to know the
material as well as the text describes. Dr. Sanders didn’t explicitly show
how the dihybrid cross illustrates Mendel’s principle of independent
assortment, but the book does, and this is a question that was asked on an
old exam.
USE YOUR BRAIN!!!!!!!
o Some questions on the exam involve critical thinking…only if you truly
understand the concept, instead of just memorizing, will you be equipped
to answer these questions on the spot. If you are having trouble
understanding how to get to the point where you are prepared to answer
questions like that, STUDY YOUR BOOK in depth or see me for
guidance.
o For each lecture, I can come up with a list of questions/concepts that
illustrate whether or not you are prepared for exm-critical thinking. Other
than that, you have no way of knowing how prepared for the exam you
really are. For example, for the above lecture, you’re doing great if you
can answer these questions:
 How does a punnett square illustrate the principle of segregation?
 How does a dihybrid cross illustrate the principle of independent
assortment?
 How does meiosis help me understand what allele combinations to
put in my punnett square?
 Can you use any symbol to represent an allele?
o Here are some other quick questions that if you can answer easily, you are
more prepared for critical thinking:
 How does the timing of meiosis occurrence in females affect
Down’s syndrome?
 What are the major differences in meiosis between males and
females?
 Can you keep track of the number of chromosomes throughout
meiosis?
 Do 9:3:3:1 ratios appear when looking at codominance and
incomplete dominance?
 How does non-disjunction in meiosis result in euploidy and
aneuploidy?
 All diseases discussed on Thursday (2/8) are either autosomal or
sex-chromosomal, and are either dominant or recessive…can you
categorize the diseases based on this?
 All diseases on the Ch. 6 handout result from non-disjunction in
meiosis AND are either euploidy, autosomal aneuploidy, or sex
chromosomal aneuploidy…do you understand these categories and
how all the diseases fit in to these categories?