Transcript Show Me the Genes 2016x

Show Me the Genes
Lesson 63
p. 47-54
Entry Task
3 friends were talking while finishing their “Gene Squares”
assignment. One said, “Okay, we get that traits are passed
through alleles - one from each parent, but what are genes
and where are they stored?”
Kelli said, “They are little cells found in the blood”
Lian said, “No, they are in the cells themselves. Genes are
spread out homogeneously, or evenly, inside every
cell”
Blake said, “I disagree. I think they are…”
Next: Complete your notes as information is presented.
Chromosomes
• Chromosomes are tiny bundles of
tightly wound strands of DNA that
can be found in the nucleus of
eukaryotic cells.
• Within each chromosome, there
are many segments, or sections,
that we commonly refer to as genes.
• There are 23 pairs of chromosomes in each human cell.
• Discuss: What would happen to the number of
chromosomes if copies were not made before cell
division?
– If copies were not made, then eventually you would run out
of chromosomes, because you would have half each time
the cell divided until there were almost none left!
Function of Cell division
• The function of cell
division in single
celled organisms is
reproduction.
(like a protist splitting
into two identical
copies)
• The function in multi-celled organisms is
growth and repair.
(like a baby growing into an adult or a scab
forming to heal a cut)
replicate and
Pair 23
• What is unique about chromosome pair
number 23?
– Chromosome pair 23 determines the gender of the
offspring. Males have an X and Y females have X and X.
Hint: Eggs always contain
an X chromosome so it is
always the sperm that
determines gender!
Human Chromosome Pairs
In sex cells…
• Discuss: Why must chromosomes in the
sperm and egg be half the number as in other
cells of an organism that reproduces sexually?
– It has to be half the number so that when the
sperm and egg come together, forming a zygote, it
has one complete set.
– This same genetic code is
then copied into every
new cell as the organisms
grows (sexual) or
reproduces (asexual).
Fertilization
Zygote
Recap: Chromosomes
• 23 pairs (46 total) in
each human cell,
except egg and sperm
• Pair #23 is
responsible for
gender
• Females have two Xchromosomes
• Males have an X- and
a Y-chromosome
Critter Examples: Generation 1
Skye
TT
TT
tt
tt
TT
T
tt
tt
TT
TT
T T
Poppy
tt
t t
T
Tt
Tt
Tt
Tt
t
t
Remember, Punnett Squares
only show the possible
outcomes, not what will
happen for sure.
Critter Examples: Generation 2
Lucy
Ocean
Tt
Tt
T t
Tt
Tt
Tt
Tt
Tt
Tt
T
Tt
T t
t
TT
Tt
Tt
tt
Tt
T
t
A pair of chromosomes
T
T
Gene – a section of DNA
B
b
N
n
There are many genes
on one chromosome
s
s
A
a
e
e
G
g
Genes hold the alleles
that determine our
traits
Parent has 46
chromosomes
(23 pair)
Parent has 92
chromosomes
(46 pair)
Made of coiled DNA
For each pair, we get
one from each parent
Daughter
cells have 46
chromosomes
(23 pair)
Flow Diagram
Now it’s your turn! Place the following terms in
order from biggest to smallest:
DNA
Cell
Chromosome
Nucleus
Allele (gene)
Flow Diagram
Cell  Nucleus  Chromosome  Allele  DNA
X
X or Y
Labeled Diagram
XX = Female
XY = Male
Your Task
Create a labeled diagram that shows the following:
• Number of chromosomes in egg and sperm cells
• Number of chromosomes (pairs) in zygotes
• 23rd Chromosome information (x from egg, x or y from
sperm).
• Gender information (xx = female xy = male)