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Pre-AP Biology – Meiosis & Genetics Study Guide
Name:___________________
1. Answer the following questions regarding meiosis.
a. What is its purpose? To create haploid gametes for sexual reproduction. The purpose of this
is to INCREASE GENETIC VARIATION.
b. Fill in the following chart demonstrating the differences between mitosis and meiosis in humans.
1
1
2
46
1
2
4
23
Centromeres
Homologous
Chromosomes
Identical
Different
Grow Repair
Replace
Make Gametes
c. What type of cells does meiosis make? haploid gametes; This way you get half of your genetic
information from mom and half from dad.
d. Describe the major occurrences in the stages of meiosis (Picture is just there to help answer the
questions).


i. Prophase I (explanation must include crossing over, tetrad, and synapse)
(Like mitosis) - Nucleus break down, spindle fibers form, chromatin goes to chromosomes
(Different from mitosis) - Homologous chromosomes synapse forming a tetrad. Crossing over
between homologous chromosomes occurs here.



ii. Metaphase I (explanation must include homologous chromosomes and the law of
independent assortment)
Homologous chromosomes line up at the metaphase plate (middle) of the cell. The law of
independent assortment means that each homologous pair lines up independently of the others.
(For example, they could line up as follows: 12 34 or 12 43)
iii. Anaphase I (explanation must include the law of segregation)
Homologous chromosomes separate. (Anaphase, apart, and away). The law of segregation just
says that alleles separate from one another. This is true because they are on the homologous
chromosomes that are separated.
iv. Telophase I
Nuclei reform – You now have 2 haploid cells.
v. PMAT II is basically just like mitosis. The only difference is that the 2 cells are now
haploid (23 chromosomes) and will divide into a total of 4 haploid cells containing 23
chromosomes still (because we have separated the sister chromatids). There is nothing to
answer for this question.
e. What happens in metaphase of meiosis that explains the laws of segregation and independent assortment?
We have 23 pairs of chromosomes THAT LINE UP INDEPENDENTLY of each other. The
information on each chromosome is inherited independent of the other (like hair color and eye
color).
The law of segregation is that our diploid homologous chromosomes separate into haploid gametes
at the end of metaphase (anaphase). This means heterozygous people can have homozygous kids.
This is the reason why recessive traits can be “hidden” but then show back up.
f.
If an intestinal cell in a grasshopper contains 24 chromosomes, a grasshopper sperm cell contains how
many chromosomes? 12 chromosomes (haploid = half)
g. If a frog gamete has 10 chromosomes, how many chromosomes are in its somatic cells?
20 diploid = double)
h. Why is it important that EVERY SEXUALLY REPRODUCING ORGANISM (humans, plants,
everything) be capable of alternating between a haploid and diploid stage in their life cycles. (For
humans, we are diploid and our reproductive cells are haploid).
So that we can get ½ DNA from mom and ½ from dad to make 1 whole baby. We live our lives as diploid
organisms, but we make haploid reproductive cells to repeat the process again.
Very Important Note: I have already tested your ability to complete and interpret Punnett squares with
the quiz we recently took. This test is mostly conceptual. In other words, there will only be a few
questions requiring the completion of Punnett squares. In order to have success on this test, you must
understand the actual physical processes involved during meiosis and heredity.
2. Explain the difference between the following & provide an example of each:
a. genotype & phenotype
Genotype = genes (remember a gene is enough DNA to code for 1 protein) – represented by letters (Ex.
TT, Tt, or tt)
Phenotype = physical trait that is coded for by the genotype (Ex. Tall or short)
b. homozygous & heterozygous
homozygous = same allele for a gene (Ex. TT or tt)
heterozygous = different allele for a gene (Tt)
c. recessive & dominant
Recessive means that the DNA sequence for that allele does not code for a functioning protein
Dominant means that the DNA sequence for that allele does code for a functioning protein. This is why
dominant alleles “mask” recessive alleles.
Note: Dominant does not mean better or more common.
d. complete dominance, incomplete dominance, and codominance
Complete dominance = Simple dominant and recessive traits like described in part c.
Incomplete dominance = Neither allele dominates the other. Heterozygous phenotype is a blend of the 2
homozygotes. (Black + white = grey)
Codominance = both alleles dominate. Heterozygous phenotype shows both homozygous phenotypes.
(black + white = black & white)
e. true breed & hybrid
True breed = homozygous
Hybrid = Heterozygous
f. autosome & sex chromosome
Autosomes = Chromosomes 1-22. Boys and girls inherit these traits at equal rates.
Sex chromosome = 23rd chromosome pair. Boys and girl inherit these traits at different rates. Boys show
these traits more while girls are carriers.
g. allele, gene, and homologous chromosome
****Need to know these
Allele = Alternative form of a gene. You get 1 allele for each gene from each parent (so 2 total alleles for
each gene). Ex. T = tall and t = short
Gene = enough DNA to code for 1 protein. Each gene is made of 2 alleles (1 from mom and 1 from dad).
Homologous chromosome = chromosomes that are that same size, same shape, and carry the same genes.
These are the chromosomes that occur in pairs (we have 23 pairs of homologous chromosomes). There
will be 1 allele for each gene on each homologous chromosome.
*** Demonstrate with beads
h. chromosome vs. sister chromatid
chromosome = 1 strand of DNA. Each chromosome contains hundreds of genes
sister chromatid = 2 identical copies of a chromosome that are held together by the centromere. This
copy is made during S phase of interphase so that each new cell gets a complete set of DNA.
***Demonstrate with beads.
i. law of segregation vs. law of independent assortment
Law of segregation = Homologous chromosomes (and the alleles that are on them) separate from each
other during anaphase I. This is how meiosis takes a diploid cell and makes haploid gametes.
Law of independent assortment = Homologous chromosomes (and the genes that are one them) line up
indepently of each other during metaphase; therefore, traits that are on different chromosomes (i.e. eye
color and hair color) are inherited independently of each other.
*** Demonstrate with beads
j. polygenic inheritance vs. multiple alleles
Polygenic inheritance (Poly=many and genic=genes) – Traits that are coded for by multiple genes. This
results in a CONTINUUM of possible phenotypes (i.e. hair color, eye color, skin color, height). To
remember this type of inheritance, think poly = many so this results in many phenotypes (hundreds of
possibilities).
Multiple alleles = There are more than 2 alleles for a single gene at a single locus. (Ex. Blood type has IA,
IB, and i alleles)
Polygenic
Multiple alleles
k. sex-linked vs. linked
Sex-linked = genes that are on the X chromosome. Guys get these traits more because they only have 1 X
chromosome so they only have to get it from mom
Linked = these traits are inherited together because they are on the same chromosome (they DO NOT
follow the law of independent assortment). In other words, if you get one of these traits then you’ll get the
other because they are “linked” together. – Ex. red hair and freckles.
l. haploid vs. diploid
haploid = only 1 member of homologous chromosome pairs. Represented by n (which means number of
homologous pairs). Gametes are the only cells that are haploid.
diploid = both members of homologous chromosome pairs. Represented by 2n (because you have 2 of
every homologous chromosome). All somatic cells are diploid.
m. monohybrid vs. dihybrid
Monohybrid = cross that involves only 1 trait (monohybrid means 1 difference). You only use 1 Punnett
square when you work these out.
Dihybrid = cross that involves 2 traits (dihybrid means 2 differences). You use 2 Punnett squares when
you work these out.
3. What happens in metaphase of meiosis that explains the laws of segregation and independent
assortment?
Law of independent assortment – The homologous chromosomes line up independently of one another.
Law of segregation – The homologous chromosomes are separated after they line up in metaphase.
4. Answer the following questions about Mendel’s P, F1, and F2 generations.
a. What does each stand for?
a. P – Parent
b. F1 – Filial 1 (first son)
c. F2 – Filial 2 (second son)
b. What was crossed in each generation?
a. P - TT x tt
b. F1 – Tt x Tt
c. F2 – nothing
c. What was the genotype/phenotype ratio of the offspring in each generation (there is space below
each if you need to do the Punnett squares)?
a. P
The offspring of the P generation is the F1 generation.
G.R. = 0:4:0
P.R. = 4:0
b. F1
The offspring of the F1 generation is the F2 generation.
G.R. = 1:2:1
P.R. = 3:1
c. F2
no offspring
5. What type of cross showing complete dominance would in a 3:1 phenotypic ratio? Show the Punnett
square.
Tt x Tt
6. If a trait for free earlobes is autosomal recessive, and a female has free earlobes, what is her genotype?
What is her phenotype?
genotype = aa
phenotype = free
7. Can a male be a carrier of an autosomal recessive disorder? Why?
Yes, both males and females can be (Aa).
8. Is it possible for a male or female to be a carrier of an autosomal dominant disorder? Why?
No. Aa would result in the dominant phenotype. You can’t be a carrier if you actually have the trait.
9. A cross was done between 2 flowers exhibiting incomplete dominance and all of the offspring were
pink.
a. Draw a Punnett square showing this crossing.
R
r Rr
r Rr
b.
c.
d.
e.
R
Rr
Rr
What are the genotypes of the parents? RR x rr
What are the phenotypes of the parents? Red x white
What is the genotypic ratio? 0:4:0
What is the phenotypic ratio? 0:4:0
10. If you were to cross two roan (red and white) cattle, what would be the chances of the offspring having a
red phenotype (assuming the gene exhibits codominance)? Show the Punnett square.
R
R RR
r Rr
r
Rr
rr
¼ = Red (RR)
11. Answer the following questions about the dihybrid cross of DdEe X DdEe.
a. Perform the Punnett squares.
D
D DD
d Dd
d
Dd
dd
E
E EE
e Ee
e
Ee
ee
b. How many of the offspring would be dominant for both traits? 9/16 (3/4 for “D” trait
dominant” X ¾ “E” trait dominant)
c. How many of the offspring would be ddee? 1/16 (1/4 dd X ¼ ee)
d. What is the phenotypic ratio? 9:3:3:1 (DD:Dr:rD:rr)
12. What fraction of the offspring would have the genotype aabbcc if we were to cross AaBbCc x AaBbCc?
Show the Punnett squares.
1/64 (1/4 aa X ¼ bb X ¼ cc)
A
a
A AA
Aa
a Aa
aa
B
b
C
c
B
BB
Bb
C
CC
Cc
b
Bb
bb
c
Cc
cc
13. If a female that is colorblind (a sex-linked recessive trait) and is crossed with a normal male, what
genotypes and phenotypes would be possible in the offspring?
Xb
XB XBXb
Y XbY
Xb
XBXb
XbY
Phenotypes = normal vision female and colorblind male
Genotypes = XBXb and XbY
14. Why are sex-linked traits expressed more in males? Why can't males be carriers of a sex linked trait?
Guys only have 1 X chromosome so they cannot be carriers. They either have the trait or they do not.
Girls have 2 X’s so they can be carriers.
15. What are the possible genotypes for the following blood types?
Blood
Genotype
Type
A
IAIA or IAi
B
IBIB or IBi
AB IAIB
O
ii
16. Could a child with type O blood have a father with type AB blood? Why? Show the Punnett square.
You have to get 1 allele from each parent. The father only has the IA allele and the IB allele.
IA
IB
A
I
IB
IA
IB
*** Show blood typing kit
17. If a woman with type A blood had a child with a man that had type B blood, what are all the possible
blood types that the child could have? Show the Punnett square. (There are multiple Punnett squares that
could be made, but one particular Punnett square would show all the possible offspring).
IA
i
B
A
B
I I I
IB i
A
i I i
ii
A, B, AB, or O
18. What types of blood can the following individuals accept in a blood transfusion?
Hint to remember: You can accept blood that is like yours or O. You can donate to blood like
yours or AB.
Blood
Types they may
Types:
receive:
A or O
A
B or O
B
A, B, AB, or O
AB
O
Only O
19. Why can't people with type O blood receive blood from anyone but other with type O?
They have both antibody A and B (because they don’t have any antigens/carbs on their red blood cells
to fight); therefore, the antibodies would fight A, B, and AB blood.
Use the pedigree below to answer questions 20
20. Answer each of the following with regard to the pedigree above.
a. Label the generations and individuals for the pedigree.
b. Is the pedigree showing an autosomal or sex-linked trait? Explain.
Sex-linked because only guys are getting it.
c. Is the pedigree showing a recessive or dominant trait? Explain.
Recessive. Guys only have 1 X chromosome so their daughters automatically get it. If it was a dominant
trait, then all the daughters of fathers with the trait would also have the trait.
d. Write the genotype for each individual under their symbol. If there is not enough information to
determine the phenotype of an individual then put a ? for the 2nd allele.
If a boy has it, his mom and daughters are all carriers.
Generation 1: Person 1=XAY, Person 2=XAXa
Generation 2: Person 1=XAY, Person 2= XAXa, Person 3=XAX?, Person 4=XaY, Person
5=XAX?
Generation 3: Person 1=XaY, Person 2=XAX?, Person 3=XAXa, Person 4=XAY
e. Individual 1 in generation III mates with a female who is a carrier for colorblindness (hint: this
helps give you the answer to b). Do all this on board
i. Draw this female into the pedigree.
ii. Create a Punnett square predicting the offspring of these 2 individuals.
XA
Xa
Xa XAXa XaXa
Y XAY XaY
iii. What percentage of their offspring would be expected to be colorblind?
50%
f. Individual 3 in generation III mates with a normal male. Do all this on board
i. Draw this male into the pedigree.
ii. Create a Punnett square predicting the offspring of these 2 individuals.
XA
Xa
XA XAXA XAXa
Y XAY XaY
iii. What percentage of their offspring would be expected to be colorblind?
25%
21. Explain why polygenic traits (like hair color, eye color, height, etc.) result in a range of hundreds of
possible phenotypes rather than a few possible phenotypes like the other types of inheritance we have
discussed.
Poly = many genes. There are many genes making many proteins so you have countless possibilities for
the phenotypes. RESULTS IN A CONTINUING RANGE OF PHENOTYPES (LIMITLESS
PHENOTYPES)
22. What is an example of linked traits, and why are these inherited together?
They are inherited together because they are on the same chromosome. Ex. red hair and freckles.
23. Circle the multiple choice answer for the following pedigree. Then answer the questions that follow.
Multiple choice answer = C (must be carrier because had recessive kid)
a. How could you tell that this pedigree was for an autosomal trait instead of a sex-linked trait
(even if it hadn’t told you by the multiple choice answers)?
Guys and girls got it equally.
b. How could you tell that this pedigree was showing the inheritance of a recessive trait and not a
dominant trait?
If it were dominant, then 2 recessive parents couldn’t have dominant kids.
24. Circle the multiple choice answer for the following pedigree. Then answer the questions that follow.
Multiple choice answer = C (8 must be carrier because had recessive son and 13 must be carrier because
had recessive father – Remember, guys only have 1 X that they must get from mom and give to
daughter).
a. How could you tell that this pedigree was for a sex-linked trait instead even if the question
hadn’t told you?
Only guys are getting it.
b. How could you tell that this pedigree was showing the inheritance of a recessive trait and not a
dominant trait even if the question hadn’t told you?
Recessive. Guys only have 1 X chromosome so their daughters automatically get it. If it was a dominant
trait, then all the daughters of fathers with the trait would also have the trait.
25. Genetic disorders occur when the number of chromosomes remains the same (46 for humans), but the
ORDER OF THE DNA BASES creates health problems. Describe the symptoms of the following
disorders.
o Autosomal dominant disorders:
a. Huntingtons
Deterioration of brain around age 40-50.
b. achondroplasia
Genetic dwarfism
o Recessive
a. sickle-cell
Red blood cells can’t carry oxygen
b. cystic fibrosis
Lungs fill with fluid and drown
o Sex-linked recessive
a. Hemophilia
Excessive bleeding
b. Colorblindness
Can see limited colors
26. Genetic syndromes occur when the normal number of chromosomes is altered because of problems
during anaphase of meiosis. Answer the following questions about these scenarios.
a. All of these syndromes are caused by nondisjunction of homologous chromosomes or sister
chromatids during meiosis. What is nondisjunction?
When homologous chromosomes or sister chromatids fail to separate in anaphase I or II.
b. What phase of meiosis does this occur in? anaphase
c. Explain how the karyotypes of each of the following syndromes would look different than a
normal karyotype. In other words, where would they have an extra or missing chromosome.
a. Down syndrome
Trisomy 21
b. Turner’s syndrome.
X_ (only 1 X chromosome – doesn’t have another X or Y)
c. Klinefelter’s syndrome.
XXY
d. Why can’t we tell if someone has a genetic disorder (i.e. colorblindness, Huntingtons,
etc.) just by looking at karyotype?
They have 46 chromosomes like everyone else.
d. What are the characteristics of individuals with the following syndromes?
a. Down syndrome
Lower mental capacity. Stereotypical facial features. Shortened life span.
b. Turner’s syndrome.
No secondary sexual characteristics of normal females (no breasts, no menstruation, etc.)
c. Klinefelter’s syndrome.
Genetically a man, but they have an increase in feminine characteristics (increased breast tissue, narrow
shoulders, wide hips, decreased facial hair, etc.)