Reebop Reproduction

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Reebop Reproduction
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You just conducted a Reebop breeding program.

• What were some of the observable differences
  between the parent Reebopsand their babies?
• What were some of theobservable
  differencesbetween the babies?
• In other words, how did thephenotypes of the
  Reebops differ?

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How did the phenotypes of the Reebops differ?

• Antennae
• Tails
• Body segments
• Humps
• Eyes
• Legs
• Noses

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Quick-Think Time

• Having Baby Reebops with identical phenotypes
  would be better for the Reebops.
• Do you agree or disagree? Explain your thinking.

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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.

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Quick-Think Time

• ThinkPairShare
• How did the Reebop babies end up being different
  from their parents andfrom each other?

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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.

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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?

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Sources of Variation Reproductive Cells
(Gametes)

• You randomly selected one copy of each Reebop Mom
  chromosome for an egg cell (female gamete).

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A
a
Q
q
E
e
D
d
M
m
T
t
L
l

• 7 pairs of Reebop Mom chromosomes
• 14 chromosomes in all

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Randomly choose one of each
A
q
e
D
m
T
L
a
Q
E
d
M
t
l
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Reebop egg
a
Q
E
d
M
t
l

• 7 single Reebop Mom chromosomes
• 7 chromosomes in all

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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).

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Quick-Think Time

• Why do you think that gametes are haploid?
• Tip What would happen every generation if
  gametes were diploid?

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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.

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Extra or Missing Chromosomes
Normal Human Karyotype
How is this Karyotype different?
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Extra or Missing Chromosomes
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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.

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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.

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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.

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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.

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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
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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

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1 diploid cell
2 identical diploid cells
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Mitosis vs Meiosishttp//www.pbs.org/wgbh/nova/ba
by/divide.html
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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.