Transcript Reebop Reproduction

Reebop Reproduction
You just conducted a Reebop
breeding program.
• What were some of the observable
differences between the parent Reebops
and their babies?
• What were some of the
observable differences
between the babies?
• In other words, how did the
phenotypes of the Reebops differ?
How did the phenotypes of the
Reebops differ?
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•
•
•
•
•
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Antennae
Tails
Body segments
Humps
Eyes
Legs
Noses
Quick-Think Time
• Having Baby Reebops with identical
phenotypes would be better for the
Reebops.
• Do you agree or disagree? Explain your
thinking.
Benefits of Variation
• Natural selection acts on random variation
that exists in a population of organisms.
• Variations provide the potential to be
adapted to changes in the environment when
they happen.
• Heritable variations already exist in the
population and do not arise because of a
change in the environment.
Quick-Think Time
Think–Pair–Share
• How did the Reebop babies end up
being different from their parents
and
from each other?
Sources of Variation:
• Each Reebop parent has two copies of each
chromosome in all of its body cells.
• A cell with two sets of chromosomes is diploid.
• Traits are determined by genes carried on
chromosomes.
• Different forms of a gene for the same trait are
called alleles.
• Both copies of a chromosome might carry the
same allele or they might carry different alleles.
Quick-Think Time
• Look at the students holding the signs.
• The “t” on each sign represents an
allele for antennae.
• If the Reebop parents have the alleles
shown on these signs, what kind of
antennae do you expect their babies to
have?
Sources of Variation:
Reproductive Cells (Gametes)
• You randomly selected one copy of
each Reebop Mom chromosome for an
egg cell (female gamete).
A
a
Q
q
E
e
D
d
M
m
T
t
L
•7 pairs of Reebop Mom chromosomes
•14 chromosomes in all
l
Randomly choose one of each…
A
q
e
D
m
T
L
a
Q
E
d
M
t
l
a
Q
E
Reebop
egg
d
M
t
l
•7 single Reebop Mom chromosomes
•7 chromosomes in all
Sources of Variation:
Reproductive Cells (Gametes)
• You randomly selected one copy of each Reebop
Mom chromosome for an egg cell (female gamete).
• Chances of selecting the exact same set of
chromosomes a second time are extremely small.
• Each egg contains one set of chromosomes.
• A cell with one set of chromosomes is haploid.
• The egg contains one allele for each trait.
• Everything just said is the same for Reebop sperm
(male gametes).
Quick-Think Time
Why do you think that gametes
are haploid?
Tip: What would happen every
generation if gametes were
diploid?
Why are watermelons big?
• Cells are polyploid if they contain more than
two (2n) sets of chromosomes (and genes).
• For example, triploid (3n) and tetraploid cell
(4n) cells are polyploid.
• Polyploidy is very common in plants,
especially in angiosperms.
• Polyploidy is much rarer in animals. It is
found in some insects, fishes, amphibians,
and reptiles.
Extra or Missing Chromosomes
Normal Human Karyotype
How is this Karyotype different?
Extra or Missing Chromosomes
Sources of Variation:
Fertilization
• You joined the egg and sperm to form a
fertilized egg.
• The chances of any particular egg
being fertilized by any particular sperm
are very small.
Quick-Think Time
Fill in the blanks.
• The fertilized egg has __________
set(s) _____of chromosomes (and
genes).
• The fertilized egg is _____ploid.
• The fertilized egg contains _______
allele(s) for each trait.
Quick-Think Time
Fill in the blanks.
• The fertilized egg has two set(s) of
seven chromosomes (and genes).
• The fertilized egg is diploid.
• The fertilized egg contains two allele(s)
for each trait.
Sources of Variation:
Summary
• Parents have two alleles for each gene.
These alleles can differ from one another,
adding potential for variation in offspring.
• Parents produce haploid gametes with a
random assortment of their chromosomes.
Each gamete is different.
• As gametes are formed, another process
called crossing over adds a great deal of
variation to the gametes.
• The many possible combinations of sperm
and egg produce even more variation.
Meiosis Basics
• You made a haploid gamete by picking strips
of paper that represented chromosomes.
• In real organisms, how do we get from the
diploid somatic cell to the haploid gamete?
A process called MEIOSIS
1 diploid cell
2 diploid cells
4 haploid cells
Mitosis Basics
• You built a Reebop baby by reading the
chromosomes in the fertilized egg.
• In real organisms, how does a single cell (the
fertilized egg) become a multicellular baby?
A process called MITOSIS
1 diploid cell
2 identical diploid cells
Mitosis vs Meiosis
http://www.pbs.org/wgbh/nova/baby/divide.html
Reebops Science Summary
• Reebop populations have genetic diversity.
Any reebop might have two different alleles
for a trait.
• The process of producing gametes (meiosis)
adds variation through random assortment
and crossing over of chromosomes.
• Fertilization adds more variation.
• Natural selection by the environment acts on
this variation by determining which
individuals survive to reproduce viable
offspring.