Chapter 13 RQ
1. What are hereditary units of information
2.
3.
4.
5.
called?
All chromosomes besides the X and Ys
are known as _____________.
What keeps sister chromatids together
until anaphase?
What is the purpose of meiosis?
What is the term for a fertilized egg?
1. Explain why organisms only reproduce their own kind, and
why offspring more closely resemble their parents than
unrelated individuals of the same species.
It is a consequence of heredity,
which results from the transmission
of genes from parents to offspring
Because they share similar genes,
offspring more closely resemble their
parents or close relatives than others

2. Explain what makes heredity possible.
DNA is precisely replicated producing
copies of genes that can be passed
along from parents to offspring
Sperm and ova carrying each parents’
genes are combined in the nucleus of
the fertilized egg 
3. Distinguish between asexual and sexual
reproduction.
Asexual
Single parent 
passes on all of its
genes
Offspring are
genetically identical to
parent
Results in a clone
Genetic differences
may occur as a result
of mutation (change in
DNA)
Sexual
2 parents  each
parent passes on ½ of
its genes
Offspring have a
unique combination of
genes inherited from
both parents
Results in greater
genetic variation –
offspring vary
genetically from their
siblings & parents 
4.
Diagram the human life cycle and indicate where in the
human body that mitosis and meiosis occur; which cells are the
result of meiosis and mitosis; and which cells are haploid.
Mitosis  somatic cells, diploid (46
chromosomes); growth
Meiosis  gametes, haploid (23
chromosomes); sperm cells and ova 
5. Distinguish among the life cycle patterns
of animals, fungi, and plants.
Animals
Gametes are the
only haploid (n)
cells
Meiosis halves the
cells (2n  n + n)
Fertilization makes
the 2n organism 
Fungi
Only diploid (2n)
stage is the zygote
Resulting haploid
(n) cells divide by
mitosis to make the
“n” organism
Gametes produced
by mitosis 
Life cycles…
Plants
Alternate generations
2n stage – sporophyte
(makes spores by
meiosis)
Haploid spores divide
mitotically to produce
a multicellular haploid
gametophyte (haploid
gametes produced by
mitosis)
Fertilization produces
a diploid zygote –
sporophyte 
6. List the phases of meiosis I and meiosis II
and describe the events characteristic of
each phase.
Meiosis I  cell division that segregates
the two chromosomes of each homologous
pair and reduces the chromosome number
by one-half; includes four phases:
1. Prophase I
2. Metaphase I
3. Anaphase I
4. Telophase I and Cytokinesis 
Meiosis I…
Prophase I  long and complex; 90% of time for
meiosis
- synapsis occurs (homologous chromosomes come
together to form a tetrad; four chromatids)
- crossing over occurs
Metaphase I  tetrads align at metaphase plate
Anaphase I  homologues separate and are moved
toward the poles by the spindle apparatus
Telophase I & cytokinesis  the spindle apparatus
continues to separate homologous chromosome
pairs until the chromosomes reach the poles 
Meiosis II…
Meiosis II  this division separates
sister chromatids of each
chromosome; includes four phases:
1. Prophase II
2. Metaphase II
3. Anaphase II
4. Telophase II and Cytokinesis 
Meiosis II…
Prophase II  spindle apparatus forms and
chromosomes move toward the metaphase II plate
Metaphase II  chromosomes align singly on the
metaphase plate
Anaphase II  centromeres of sister chromatids
separate, sister chromatids of each pair move
towards opposite poles of the cell
Telophase II and cytokinesis  nuclei form at
opposite poles of the cell
- cytokinesis occurs producing four haploid
daughter cells 
7. Describe the process of synapsis during
prophase I, and explain how genetic
recombination occurs.
Synapsis 
homologous
chromosomes come
together as pairs
Crossing over can
happen where the
nonsister
chromatids are
linked 
8. Describe key differences between mitosis
and meiosis; explain how the end result of
meiosis differs from that of mitosis.
Meiosis
1. Is a reduction division
2. Creates genetic variation
3. Is 2 successive nuclear divisions
- produces gametes in animals
Mitosis
- crossing over doesn’t occur
- occurs in somatic cells (body cells)
- copies the cells 
9. Explain how independent assortment, crossing
over, and random fertilization contribute to genetic
variation in sexually reproducing organisms.
Independent assortment – orientation of the chromosome
pairs is random at the poles (meiosis I)
- each homologous pair orients independently of the others
at metaphase I
Crossing over – exchange of genetic material between
homologues (prophase I)
- occurs when homologous portions of 2 nonsister chromatids
trade places
Random fertilization – an egg is representative of 1 in 8
million possible chromosome combinations (same with sperm)
- resulting zygote can have 1 in 64 trillion possible diploid
combinations (not including crossovers) 
10. Explain why inheritable variation was
crucial to Darwin’s theory of evolution.
It is the basis for natural selection
- variations selected that increase
reproductive success
- adaptation (the accumulation of
heritable variations) 
11. List the sources of genetic variation.
1. Sexual reproduction  independent
assortment, crossing over, random
gamete fusion
2. Mutation  random and rare
structural changes made during
DNA replication in a gene that could
result from mistakes 