Why does reproduction require 2 types of cell division? Asexual & Sexual Reproduction.

Why does reproduction

require 2 types of cell division?

Asexual & Sexual Reproduction

Asexual reproduction & cell division

• Asexual reproduction is reproduction involving only one source of genetic material (i.e. one parent).

• This means that offspring are genetically identical to the parent, or clones.

Several types of asexual reproduction:

• Binary fission occurs when a unicellular organism (such as bacteria or an amoeba) divides into two equally sized cells for the purpose of reproduction.


• Budding occurs when simple organisms (such as yeast or hydra) produce much smaller cells than those of the parent organism.


• Sporulation occurs when an organism (such as mushrooms) produce spores - tiny packets of DNA - for the purpose of reproduction.


• Vegetative propagation occurs when a portion of a plant goes through cell division in order to produce another plant.


• Regeneration occurs when a part of an animal (such as an earthworm) undergoes cell division to produce a new organism.

Fill It In …Simple pictures of asexual reproduction:

Binary fission

Budding

Sporulation

Vegetative propagation

Regeneration

Advantages & Disadvantages of Asexual Reproduction

• Advantages– Advantages of asexual reproduction include speed of reproduction and producing multiple copies of successful genetic combinations.

Advantages & Disadvantages of Asexual Reproduction

• Disadvantages– Disadvantages of asexual reproduction include increased risk of a single factor affecting an entire population due to lack of genetic variation

• Mitosis is usually the mechanism that allows asexual reproduction to occur.

• For example, when an earthworm is cut in half, cells must use mitosis to divide in order to produce cells which will reconstruct the missing portion

Sexual reproduction & cell division

• Sexual reproduction is reproduction involving two sources of genetic material (i.e. two parents).

• This means that offspring will be genetic combinations of the two parents.


• Gametes are sex cells, such as sperm and egg

• The purpose of a gamete is to fuse with another gamete to combine genetic material (fertilization).


• A zygote is the cell which is produced by fertilization.

• The zygote will develop into an embryo.

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Picture of fertilization:

Advantages & Disadvantages of Sexual Reproduction

• Advantages– The main advantage of sexual reproduction is genetic variation.

– With many genetic possibilities, the likelihood of a successful combination of traits for a particular environment is high

Advantages & Disadvantages of Sexual Reproduction

• Disadvantages– The disadvantages of sexual reproduction include the necessity of mating for fertilization (which requires more time) and the risks of unfavorable genetic combinations.

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Summary: Advantage Disadvantage

Asexual

Sexual

• Although sexual reproduction begins differently than asexual reproduction (with two parents as opposed to one parent), sexual reproduction also relies on cell division

Crossing Over- MYP

Segregation of Alleles- MYP

Meiosis• Meiosis is a type of cell division which produces gametes.

• Meiosis is a unique type of cell division because it divides the genetic material in half, allowing for fertilization.

Meiosis• Example: Human body cells contain 46 chromosomes

• In order for a zygote (fertilized egg) to contain 46 chromosomes, the sperm and egg must each contain only 23 chromosomes

• Mitosis is the process which allows the zygote to begin dividing to produce a multicellular organism.

• The cells must also differentiate (become different types of cells to carry out different functions)

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In sexual reproduction …Job of meiosis -

Job of mitosis -

Check Yourself!1. How many sources of genetic material are

involved in asexual reproduction? In sexual reproduction?

2. Name five types of asexual reproduction.3. Why is mitosis necessary for asexual

reproduction?4. Name one advantage and one disadvantage of

asexual reproduction.5. What are gametes? How is a zygote produced

from gametes?6. Name one advantage and one disadvantage of

sexual reproduction.7. How are both mitosis and meiosis necessary

for sexual reproduction?

Check Yourself!1. How many sources of genetic material are

involved in asexual reproduction? In sexual reproduction?

ASEXUAL - ONE SOURCE/ONE PARENT SEXUAL - TWO SOURCES/TWO PARENTS

Check Yourself!2. Name five types of asexual reproduction. BINARY FISSION BUDDING SPORULATION VEGETATIVE PROPAGATION REGENERATION

Check Yourself!3. Why is mitosis necessary for asexual

reproduction? TO PRODUCE GENETICALLY IDENTICAL

DAUGHTER CELLS

Check Yourself!4. Name one advantage and one disadvantage of

asexual reproduction. ADVANTAGE - SPEED MULTIPLE COPIES DISADVANTAGE - NO GENETIC VARIATION

Check Yourself!5. What are gametes? How is a zygote

produced from gametes? GAMETES ARE SEX CELLS (SPERM OR EGG) ZYGOTES ARE PRODUCED BY THE

FERTILIZATION OF GAMETES

Check Yourself!6. Name one advantage and one disadvantage of

sexual reproduction. ADVANTAGE - GENETIC VARIATION DISADVANTAGE - TAKES TIME RISK OF

UNFAVORABLE GENETIC

COMBINATIONS

Check Yourself!7. How are both mitosis and meiosis necessary

for sexual reproduction? MEIOSIS - CREATES GAMETES; CUTS

CHROMOSOME NUMBER IN HALF

MITOSIS - GROWTH OF A MULTICELLULAR ORGANISM

How does meiosis produce gametes?

• Recall that a gamete is very different from a somatic (body) cell.

Somatic cells & gametes

• A somatic cell is diploid, which means that it contains two of each type of chromosome.


• These chromosome pairs are called homologous chromosomes.

• For example, a human has 23 types of chromosomes.

• A human somatic cell has 46 total chromosomes, consisting of 23 homologous pairs.


• A gamete is haploid, which means it contains only one of each type of chromosome (one from each homologous pair).

• For example, a human egg cell (ovum) contains 23 total chromosomes.

Diploid vs Haploid

Fill It In …

# of chromosomes in a human …DIPLOID cell ______

HAPLOID cell ______

Eukaryotic Cell Cycle & Meiosis• At the end of

interphase (the longest part of the cell cycle in which the cell completes normal life functions), the cell duplicates the DNA.

• This creates doubled chromosomes.

• The cell is now ready to divide.

Meiosis requires 2 cell divisions:

• Meiosis I is called the reduction division.

• In this division, the homologous pairs of doubled chromosomes are separated.

• The end result of Meiosis I is two daughter cells, each of which is haploid but contains doubled genetic material

Meiosis requires 2 cell divisions:

• Meiosis II uses the same basic steps as mitosis.

• In this division, the doubled chromosomes are separated.

• The end result of Meiosis II is four daughter cells, each of which is haploid and contains no duplicated DNA.

Graphical representation of Meiosis:

46doubled

23doubled

23singled

23doubled

23singled

23singled

23singled

Meiosis I

Meiosis II

Fill It In …

46doubled

23doubled

23singled

23doubled

23singled

23singled

23singled

Meiosis I

Meiosis II

Label each of the cells in the diagram as “diploid” or “haploid”

Meiosis provides several sources of genetic variation:

• Gene mutations can occur during the duplication of DNA at the end of interphase before meiosis (or mitosis) begins.


• Crossing over occurs when the homologous pairs come together during Meiosis I (Prophase I).

• In crossing-over, a part of one chromosome can switch places with the same part of the homologous chromosome.


• Then, when the homologous pairs are separated, each chromosome will be different than the original.


• Random assortment of chromosomes into daughter cells during Meiosis I allows for a mix of the chromosomes inherited from each parent.


• Nondisjunction, when homologous chromosomes do not properly separate, may occur during Meiosis I or II, creating a gamete with one too many or one too few chromosomes.


• The random fertilization of any one egg by any one sperm allows for numerous genetic combinations in offspring.

Fill It In …

Summary of sources of genetic variation:

1.2.3.4.5.

Check Yourself!1. How is the chromosome number of a gamete

different from the chromosome number of a somatic cell?

2. What types of cells are diploid? Haploid?3. What is the purpose of meiosis?4. What is another name for Meiosis I?5. How is the purpose of Meiosis I different

from the purpose of Meiosis II?6. Name five sources of variation Meiosis

provides.7. Describe crossing-over.

Check Yourself!1. How is the chromosome number of a gamete

different from the chromosome number of a somatic cell?

GAMETES HAVE 1/2 THE NUMBER OF CHROMOSOMES

Check Yourself!2. What types of cells are diploid? Haploid? DIPLOID = SOMATIC OR BODY CELLS HAPLOID = GAMETES OR SEX CELLS

Check Yourself!3. What is the purpose of meiosis? TO CREATE HAPLOID CELLS (CELLS WITH 1/2

THE “NORMAL” CHROMOSOME NUMBER)

Check Yourself!4. What is another name for Meiosis I? REDUCTION DIVISION

Check Yourself!5. How is the purpose of Meiosis I different

from the purpose of Meiosis II? MEIOSIS I CREATES HAPLOID DOUBLED

CHROMOSOMES MEIOSIS II CREATES HAPLOID SINGLE

CHROMOSOMES

Check Yourself!6. Name five sources of variation Meiosis

provides. GENE MUTATIONS CROSSING OVER RANDOM ASSORTMENT NONDISJUNCTION RANDOM FERTILIZATION

Check Yourself!7. Describe crossing-over. CROSSING-OVER OCCURS WHEN HOMOLOGOUS

PAIRS COME TOGETHER (OVERLAP) DURING PROPHASE I.

PART OF ONE CHROMOSOME SWITCHES PLACES WITH THE SAME PART OF THE HOMOLOGOUS CHROMOSOME.

THIS RESULTS IN A NEW COMBINATION OF GENETIC MATERIAL.

Why does reproduction require 2 types of cell division? Asexual & Sexual Reproduction.

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