Asexual Reproduction

Sexual Reproduction

Requires a male and a female Requires a sperm and an egg cell Offspring are not identical to each other

or their parents. How do offspring and parents compare

when using asexual reproduction?

Meiosis

Cell division that results in the production of the sperm or egg

Also known as Reduction Division

Meiosis

Occurs in the gonads (ovaries and testes)

Results in gametes (sperm and eggs) Results in Haploid (monoploid) cells-

cells that have half the normal number of chromosomes found in body cells

Meiosis

The sperm and egg that form from meiosis are haploid (1N)

When the sperm fertilizes the egg, the zygote that forms is diploid (2N)

All body cells arise from the zygote by Mitosis, therefore body cells are diploid

Meiosis

Meiosis involves two successive divisions which will result in four new haploid cells

The two division are known as Meiosis 1 and Meiosis 2 - both have prophase, metaphase, anaphase and telophase

Prophase 1

Each wound up DNA is double stranded Each side is called a Chromatid The two chromatids are held together

by a Centromere

Homologous Chromosomes have the same size and shape

PROPHASE 1

Information on the chromosomes are called genes

Each gene controls for one trait There are many genes on one

chromosome Genes on the same chromosome are

called LINKED

A

B

PROPHASE 1

During Prophase I the Homologous chromosomes pair up (synapsis) to form a bivalent or tetrad structures.

Synapsis brings the homologous chromosomes side by side and

intertwines thechromatids

PROPHASE 1

Parts of one chromosome may break off and switch places with the other

A

B

a

b

PROPHASE 1

Crossing -over will result in new gene combinations

a

B

A

b

Some genetic material is exchanged between two chromatids of homologous chromosomes.

1. What happens during crossing over?

The chromosomes of some gametes are recombinant, meaning that they have a combination of genetic material that differs from the diploid cell’s chromosomes.

2. How are the resulting gametes affected by crossing over?

METAPHASE 1

During Metaphase I the chromosmes will be pulled by the spindle to line along the equator

The chromosomes line up double file in homologous pairs

ANAPHASE 1

Homologous Pairs of chromosomes get pulled apart (Segregation)

The chromosomes remain double stranded

TELOPHASE 1

The cytoplasm divides (cytokenesis) Each new cell has only half the number

of the original chromosomes (reduction division)

INTERKINESIS

Resting Stage

Meiosis 1 Animation

PROPHASE 2

Prophase 2 is similar to Prophase 1 except that there are now 2 cells with half the number of chromosomes

METAPHASE 2

the chromosomes line up along the equator single file

ANAPHASE 2

The centromeres have uncoupled The spindles pull the chromatids apart The chromosomes are now single stranded

TELOPHASE 2

The cytoplasm splits leaving four cells with half the number of chromosomes

Meiosis 2 Animation

Link to Demo

Link to Quiz

two non-identical haploid daughter cells1. What is the result of meiosis I?

2. How does the movement of chromosomes in meiosis I differ from that in mitosis? In meiosis I, homologous chromosomes are separated from each other. In mitosis, sister chromatids are separated from each other.

four non-identical haploid daughter cells1. What is the result of meiosis II?

2. How are the cells at the start of prophase II different from those at the end of meiosis II?The cells in prophase II have duplicate copies of their chromatids (double stranded). The final cells have single copies.

Sexual Recombination

Creates a greater diversity of individuals in the next generation

It involves three major processes1. Crossing Over2. Independent Assortment3. Gametic Assortment

Independent Assortment

New cells are not identical to each other Each cell has different combinations of

chromosomes in them - one from each homologous pair of chromosomes

There are >8 million chromosome combinations to make each sperm or egg cell

the two different ways in which the chromosomes in this cell can be distributed during meiosis

1. What do Possibility 1 and Possibility 2 represent?

2. What circumstance determines the particular combinations of gametes that result from meiosis?the way in which the homologous chromosomes line up during metaphase I and then separate

Gametic Assortment

Each of the >8 million possible sperm cells could combine with one of the >8 million possible egg cells to form a baby

By sexually combining a sperm with an egg, there are >70 trillion possible sperm-egg combinations in each human mating

This is why you don’t look exactly like your brother or sister, even if you had the same parents

>8Million

>8Million>70 Trillion

Sexual Reproduction

What are the 3 ways presented in which Meiosis and sexual recombination makes genetically diverse individuals?

How do individuals that reproduce asexually compare with each other?

What kind of environment favors asexual reproduction? Sexual?

Seminiferous tubules

Unequal cytokinesis

Stop Three-Parent Babies Scientists: Regulate Fertility Clinics To Prevent Babies with New Genes

N E W Y O R K, May 18 1997 — Scientists are calling for the immediate regulation of fertility clinics to prevent the birth of any future gene-altered babies,

the first of which was reported earlier this year. STORY HIGHLIGHTS In March, a team of fertility specialists at the Institute for Reproductive Medicine and Science of St. Barnabas, in West Orange, N.J., reported "the first case of human … genetic modification resulting in normal healthy children."

Fertility Method Creates Gene-Altered Babies

The group used a method that extracted cellular material from a donor woman's egg cell and transferred it into an infertile woman's egg. This material allowed the woman's egg to become fertile.

The donor egg contained DNA from mitochondria, little organs inside the cell that create the energy to do life's work. The group believes that problems with the mitochondria prevented the infertile women from becoming pregnant.

Mitochondria contain only about 0.03 percent of a cell's DNA, but that's enough that they can make copies of themselves when the cells divide. The other 99.97 percent of a cell's DNA comes from the nucleus and the 23 pairs of chromosomes.

The group says that transferring this mitochondrial DNA into the recipient eggs resulted in the birth of 30 babies, the first of which was born in 1997.

Extra Genes From Mitochondria

In March, the group reported for the first time in the medical journal Human Reproduction that genetic tests on two babies showed they had DNA from three parents: Two babies born with this method actually had mitochondrial genes from the donor mom, as well as chromosomal genes from the mother and father.

This extra-parental mitochondrial DNA could be transferred to the next generation.

Scientists in the latest issue of the journal Science are calling for the regulation of fertility clinics to prevent this practice from continuing.

"No research or clinical application involving humans should proceed that have the direct or indirect potential to cause inheritable genetic modification in either the public or private sector," unless it is reviewed by already existing federal regulators or a new body, wrote Mark S. Frankel and Audrey Chapman.

Both authors preside over public policy programs at the American Association for the Advance of Science, which publishes Science.

The two authors warn that efforts to modify genes transmitted to future generations could bring about both a medical and social revolution.

Social and Safety Consequences of Technology

"The dilemma is that inheritable genetic modification techniques developed for normal therapeutic purposes are also likely to be suitable for genetic alterations intended to improve what are already 'normal' genes," they write.

They warn that in a market economy the division between the haves and have-nots would increase if those who could pay could add "inherited advantage to the benefits of nurture and education already enjoyed by the affluent."

Safety concerns are also paramount, the authors say. It remains unclear how future generations with such genetic changes would fare.

"We have little experience and no evidence of long-term safety of inheritable genetic modification, whether intended or inadvertent," they write.

"There has not even been public consideration of how one would proceed in determining safety across generations. We should begin establishing an oversight process now so that we can make informed and reasoned choices about the future."

Link to Meiosis Quiz

Lack of anchorage dependence too

Contact Inhibition

Fern Life Cycle