Ch.8 continued
Sexual reproduction
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What does the term
homologous mean?
 Same or same
function
 How many
chromosomes are
there in this picture?
 2, 4 chromatids
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Are the versions (alleles) of the
genes identical on homologous
chromosomes?
Not necessarily, notice in the
picture the darker and lighter
version of the genes.
Are genes always at the same
location (locus) on the
homologues?
Yes, Blue,green and purple are
always in the same location
What do we call the chromosomes
that are the same for both females
and males (1-22)?
Autosomes
The X and Y are called the _____
chromosomes
Sex chromosomes
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What does diploid mean?
The cell has two sets of
homolgous chromosomes, one
set from mom and one from
dad.
What does haploid mean?
One set of chromosomes.
What are the two types of
gametes produced during
meiosis (sexual cell division)
and are they haploid or diploid?
Sperm and egg are haploid
When do human cells become
diploid?
After fertilization - sperm (23)
meets egg(23) = zygote (46)
The stages of meiosis are
different from mitosis
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When are the chromosomes
duplicated?
S phase of interphase
What do you notice happening
during prophase?
Crossing over
What do you think is happening
during crossing over?
Pieces of homologous
chromosomes are breaking off
and exchanging
How do the chromosomes line
up at the equator?
They line up as homologous
pairs
The stages of meiosis
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Unlike mitosis which
had 1 division, how
many divisions in
meiosis?
 2
 How do the
chromosomes line up
this time, in division
2?
 In a single file since
the homologous
chromosomes were
already separated.
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What are some of the
differences between
mitosis and meiosis?
Mitosis
Meiosis
1 division
2 divisions
Chromosomes
line up at single
file
Chromosomes
line up as
homologous
pairs
Produces 2
identical diploid
cells
Produces 4
different haploid
cells
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What is the difference between
these two pictures?
Left both blues are on the left,
right blue and red are on
opposite sides
How many different possibilites
for human combinations?
223 = 8 million combinations
with our 23 homologous
chromosomes
How does this show
independent assortment?
Where the one set of
chromosomes (large set) goes
has nothing to do with where
the other set(Small set) goes.
Independent assortment
More independent assortment
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What type of
chromosomes are these?
Homologous
How do we know they are
homologous?
They have the same
genes, only the versions
are different.
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What versions of the
genes did the mouse on
the right inherit?
 The recessive white coat
and red eyes.
 What about the mice on
the left?
 We don’t know because
they have the dominant
traits theymay have the
recessive homologuos
chromosome as well.
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What is happening in
this picture?
 Crossing over
 What is the chiasma?
 The location where
crossing over
happens.
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How many different
combinations from
crossing over?
 4, 2 the same as
original, 2
recombinants
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What process is being
illustrated?
 Karyotyping
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What is the sex of this
person?
Female
Do they have the normal
number of
chromosomes?
Yes
Are there any genetics
problems?
You can’t tell from this
karyotype
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Is this a normal
Karyotype?
 No, one too many
chromosome 21s Down’s Syndrome
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What does this graph
show?
 As age of mother
increases the number
of Down’s syndrome
births increases
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When meiosis goes
wrong, what is it called?
Nondisjunction
What happened to the
number of chromosomes
in each gamete?
Two have one too many,
two have one too few.
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How many gametes are
affected by
nondisjunction in meiosis
II?
Two, one has n+1 and
one has n-1
When the egg with too
many is fertilized by a
normal sperm the zygote
will have ___ extra
chromosome(s)
1
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What causes Klinefelter’s
syndrome?
One or more extra X
chromosomes
Why might that cause
infertility?
Mismatched
chromosomes cannot line
up correctly at metaphase
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What is the sex of this
person?
 Male with Klinefelter’s
syndrome
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Which of the sex
syndromes is most
likely to happen?
 Metafemale
X0 - Turner’s syndrome
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The fact that women
with Turner’s
syndrome have heart
problems tells you
what about the X
chromosome?
 There must be gene
on the X for heart
formation
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Which chromosomal
defect is the worst?
 A deletion
 Which defect is
probably the least
problematic?
 Inversion
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What is the Philadelphia
Chromosome?
When chromosome 22
has a piece of 9 - leading
to a type of leukemia
What causes Cri du
Chat?
A deletion on
chromosome 5
Gender testing