Name: ______________________________
Date: _________________
Unit 5B Study Guide:
Complete the following table:
Asexual Reproduction
Sexual Reproduction
Requires more time
- Provides genetic _____diversity____
because DNA comes from both parent
cells
- Advantageous in varying
environments.
Fast!
- All organisms ____identical___.
- This is an advantage if conditions are
favorable and a disadvantage of they
are not.
The Label the following in this diagram; sister chromatids, homologous pairs, centromere.
Then, fill in the blanks in the box.




Homologous chromosomes are corresponding
chromosomes one which comes from mom and the
other that comes from dad.
Though these chromosomes have the same genes,
they DO NOT have the same nucleotide sequence.
Sister chromatids are genetically identical to each
other.
Each chromosome in each pair is double armed.
What types of cells have all of the DNA? _________body cells___________ AKA
_________somatic cells______________.
Cells with both sets of chromosomes (all of the DNA) are called ____diploid____ (2n).
What types of cells will have only half the amount of the DNA? _______sex cells_____ (sperm
and egg) AKA ________gametes_____________
Cells with one set of chromosomes (half the DNA) are called ___haploid__ (n).
[Type text]
Complete the following table:
Organism
Number of
chromosomes in
each body cell
(2n)
Number of
chromosomes in a
each sex cell (n)
Corn plant
20
10
Housefly
12
6
Fruit fly
8
4
Complete the graphic organizer:
Mitosis
Fertilization
23
(n)
egg
23
(n)
+
46
(2n)
46
(2n)
46
(2n)
sperm
=
46 (2n)
Mitosis
zygote
46 (2n)
46 (2n)
Mitosis
46 (2n)
List the three sources of genetic variation that result from meiosis and sexual reproduction:
1. ___Crossing over_________
2. ___Independent assortment____
3. ___Random combination of sperm and egg___
[Type text]
Use the graphic organizer of meiosis to review the key points during the production of gametes.
Be sure to label and define in your own words: tetrads, crossing over, independent
assortment, and nondisjunction.
Meiosis I
Stage
Interphase I
Description
-Growth
-DNA replication
-Preparing for cell division
Prophase I
-Crossing over occurs when
pieces of nearest chromatid
(between homologues) trade
places.
-Chromatin condenses to
chromosomes
-Spindle form
-Nuclear envelop disappears
-Homologous chromosomes pair
up (tetrads)
Metaphase I
-Independent assortment occurs
when homologous pairs line up
randomly across the middle of
the cell
-Homologous pairs (tetrads) line
up in the middle
-Spindle fibers attach at the
centromere
Anaphase I
Nondisjunction can occur here
-Spindle fibers pull homologous
pairs apart
Telophase I
-Nuclear envelop returns
-Spindle fibers break down
-Sometimes chromosomes relax
to chromatin
-Cleavage furrow or cell plate
begins to form
Cytokinesis I
-Cytoplasm splits
-End up with 2 cells that have a
haploid number of double
armed chromosomes
Picture
[Type text]
Meiosis II
Stage
(Interphase II)
Description
-Not a true interphase
-Most cells skip this step
-NO additional DNA replication
Prophase II
-If necessary, chromatin
condenses to chromosomes
-spindle forms
-Nuclear envelope goes away
Metaphase II
-Double armed chromosomes
line up in the middle
-Spindle attaches at the
centromere
Anaphase II
Nondisjunction can occur here
-Sister chromatids split apart and
move to opposite sides of the
cell
Telophase II
-Nuclear envelope comes back
-Spindle breaks down
-Chromosomes relax into
chromatin
-Cleavage furrow or cell plate
begins to form
Cytokinesis II
-Cytoplasm splits
-End up with 4 cells with a
haploid number of single armed
chromosomes
Picture
[Type text]
Describe what is happening in this picture:
_Homologous chromosomes are exchanging parts
of their chromosomes with each other (crossing
over)._________
In which phase of meiosis does this occur?
_______During Prophase I____
Define gametogenesis: __Gametogensis is the production of gametes or sex cells using the
process of meiosis.
______________________________________________________________________________
Use the diagrams below to describe how gametogenesis is different in males and females.
Process:___Oogenesis__
Result:
_Production of 1 egg cell
______________________
Process:_Spermatogenesis
Result:
_Production of 4 sperm
cells_________________
[Type text]
Most chromosomal disorders (like Down syndrome) result from the improper separation of
chromosomes during meiosis. This is called __Non-disjunction____.
What is trisomy? _An extra chromosome in a gamete (sex cell) which leads to an offspring with
3 copies of a chromosome._______________________________________________________
_____________________________________________________________________________
Analyze the following karyotype:
a. Is this from a human cell?
___Yes______
b. How do you know?
_23 homologous pairs__________
c. What chromosomal disorder
does this patient have?
___Edwards’ syndrome/trisomy
18
d. Is this a male or female?
____Female_____________
Match the phase of meiosis to the statement that describes it:
__BC___ Nucleus reforms around 23 single armed chromosomes as cleave
furrow forms
__C___ Spindle fibers attach to homologous chromosomes line up along
“equator” or middle of cell
__AC___ Nucleus breaks down, centrioles migrate, and chromatin condenses
into 23 double armed chromosomes
WORD BANK
a. Interphase I
b. Prophase I
c. Metaphase I
d. Anaphase I
__B___ Nucleus breaks down, centrioles migrate, tetrads form, crossing over
occurs, chromatin condenses into 46 double armed chromosomes
e. Telophase I
__D___ Spindle fibers shorten and pull apart homologous chromosomes
ab. Interphase II
__BC___ 4 gametes are formed from 2 haploid cells
ac. Prophase II
__AD___ Spindle fibers attach to centromeres of 23 double armed
chromosomes
ad. Metaphase II
__E___ 2 haploid cells with double armed chromosomes are formed in this
process
ae. Anaphase II
__AE___ Spindle fibers shorten and pull apart sister chromatids
bc. Telophase II