1

Asexual Reproduction

Section 5.4

2

Objectives

• SWBAT compare and contrast binary fission and mitosis.

• SWBAT describe how eukaryotes reproduce through mitosis.

3

Vocabulary

• Asexual reproduction• Budding• Fragmentation• Binary fission

4

Question to Contemplate

• What is asexual reproduction?

5

Reproduction

• Reproduction – process that makes new organisms from one or more parent organisms.– Sexual reproduction – involves the joining of two

specialized, haploid, cells called gametes.• Gametes are egg and sperm cells.

– Asexual reproduction – the creation of offspring from a single parent – it involves no gametes and the offspring are genetically identical to the parent.

6

Binary Fission

Most prokaryotes (remember, no nucleus) reproduce through binary fission. At right is the last stage of

binary fission in an amoeba. Above is binary fission in a paramecium.

7

Binary Fission

• Binary Fission – the asexual reproduction of a single-celled organism by division into 2 roughly equal parts. – binary fission and mitosis are have similar results.

Both processes form two genetically identical daughter cells.

– Bacteria and other prokaryotes have one “ring-shaped” chromosome in the cytoplasm, no nucleus, and no spindle fibers.

8

Binary Fission

• Binary fission starts when the chromosome ring is copied. – The two rings are attached to the cell membrane.– As the cell grows and elongates, the chromosomes

move away from each other.– When the cell is 2X its original size, it undergoes

cytokinesis.• Cleavage takes place, new cell membrane is laid down

between the 2 identical daughter cells.

9

Binary Fission

parent cell

DNA duplicates

cell begins to divide

daughter cells

10

Advantages to Asexual Reproduction

• In stable environments, asexual reproduction can be very effective and efficient – more so than sexual reproduction.

• In stable environments, genetic variation could be unnecessary or even a drawback (if you are perfectly suited for an environment, why would you want change?).

• Asexual reproduction allows for very rapid reproduction and can be a competitive advantage over sexual reproduction.

11

Advantages to Asexual Reproduction

• All of the individuals of an asexually reproducing population can reproduce.

• In a sexually reproducing population roughly half the population (this is highly dependent on the species) does not produce offspring.

12

Disadvantages to Asexual Reproduction

• Genetically identical offspring will respond to the environment in the same way.– This is a problem if the environment is not stable and the

genetically identical population is not able to cope.– In unstable environments, the genetic diversity that can

come from sexual reproduction is important to helping an organism to adapt.

– Species that reproduce asexually always are capable of reproducing sexually (by conjugation in bacteria).

– Sexual reproduction is more costly to organisms – and slower (not as efficient).

13

Conjugation in bacteria

Bacteria swapping DNA

14

Sexual Reproduction

• Sexually reproducing organisms must attract a mate. – This takes time and energy – it is a significant cost.

– There is also a lot of structures (the plumes of a

quetzal or peacock, antlers on a deer, etc.), signals, and behaviors that have evolved for attracting and picking mates.

– Asexual reproduction does not come with these costs.

15

16

Plasmid Integration

17

Some eukaryotes reproduce through mitosis – Ex 1. Budding

bud

Hydra

Yeast

Budding is when a small projection of tissue grows on the surface of the parent – eventually becoming a new individual. Growth is through mitosis – there is no recombination.

The new individual may live independently (like the hydra will) or as part of a colony like yeast.

18

Reproduction through Fragmentation

Parent organism splits into pieces, each of which grows, through mitosis, into a new individual.

19

Vegetative Reproduction

Plants are masters of asexual reproduction. Vegetative reproduction is when a new individual develops through the modification of the original organism’s tissues (for example, the modification of roots or stems).

Prairie grasses, strawberries, potatoes, and many, many other species can reproduce this way.