Reebop Reproduction

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?

How did the phenotypes of the Reebops differ?

• 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 aQ q

E eD d

M mT t

L l

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

A

aQ

q

E

eD

dM

mT

t

L

l

Randomly choose one of each…

• 7 single Reebop Mom chromosomes• 7 chromosomes in all

aQ

Ed

Mt

l

Reebop egg

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 Meiosishttp://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.