Unit 8
Meiosis
Meiosis is the source of your Uniqueness!•Why do you share some but not all of the characteristics of your parents ?
•Why do you look similar but not identical to your siblings?
•Meiosis is where we find the answers to these questions!
Meiosis Does TWO equally important things
1) Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid).
2) Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives. This creates genetic diversity which is important for the evolution and survival of the species.
Why halve the chromosomes in sex cells?
•At fertilization the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents.
•It is a way to ensure that the integrity of the species is preserved and that the offspring are viable.
• Gametes are reproductive cells that unite during sexual reproduction to form a new cell called a zygote.
• In humans, male gametes are sperm and female gametes are eggs or ovums.
• They contain ½ of the normal chromosome number for the species. • Human gametes have 23 chromosomes.
EGG SPERM
What Are Gametes?
How Are Gametes Produced?
• Gametes are made through a special type of cell division called meiosis.
• In humans, Meiosis occurs in the ovary of the female to produce egg cells and in the testicles of the male to produce sperm cells.
What are Homologous Chromosome pairs ?• They are a paired up set of
chromosomes where one comes from the mother (called a maternal chromosome) and one comes from the father (paternal chromosome).
• Homologous chromosomes are similar but not identical. Each carries the same genes in the same order, but the traits may not be the same.
What is Crossing Over?Crossing over is the exchange of segments between homologous chromosomes resulting in new combinations of genes. It provides for genetic variety in offspring.
• A karyotype is a picture of all the chromosomes from an individual’s cells.
• A karyotype is a test used to check for chromosome abnormalities. A picture of a person’s chromosomes is created by staining the chromosomes with a special dye, photographing them through a microscope and arranging them in pairs.
• A karyotype gives information about the number of chromosomes a person has, the structure of their chromosomes and the sex of the individual.
Boy or Girl ?
Homologous pair # 23 in humans determines gender !
XX = girlXY = boy
Human Reproduction Anatomy
The role of the female reproductive system is to produce eggs, and if an egg is fertilized, to nourish a developing baby until birth.
The Female Reproductive System
Important Structures:
The Male Reproductive System
•The role of the male reproductive system is to produce sperm.
•Sperm are tiny packages of chromosomes that can swim to fertilize the egg.
Important Structures:
Conception/ Fertilization• Upon ejaculation there is a release of 300-500 million sperm
• The female egg needs to be in oviduct / fallopian tube.
• All the sperm work to dissolve a protective goo surrounding the egg.
• Immediately after entry of ONE sperm, there is an instant biochemical change in zygote and no more sperm are allowed in.
In humans, a sperm enters an egg, and the two nuclei combine to form a zygote with 46 chromosomes.
This occurs in the fallopian tube or oviduct.
Fertilization
Cleavage
The fertilized egg, called a zygote undergoes cell division to produce a two-celled embryo. These cells divide again and again to form a ball of cells. This series of mitotic cell divisions is called cleavage.
•Three days after fertilization, the embryo is a solid ball of about 50 cells called the morula.
3 Days After Fertilization
7 Days After Fertilization
As the embryo grows, a fluid filled cavity forms in the center turning the embryo into a hollow structure. It is now known as a blastula. It secretes enzymes that allow it to embed itself into the wall of the uterus. This is called implantation.
Implantation is the process where the fertilized egg is embedded into the lining of the uterus.
An ectopic pregnancy occurs when the egg is incorrectly embedded into the wall of the fallopian tube. This is not a viable pregnancy and is a danger to the mother.
Embryonic Stem Cells and Differentiation
• Stem cells are undifferentiated cells that are capable of dividing for long periods of time and can give rise to specialized cells under particular conditions.
• When allowed to grow in particular environments, stem cells divide many times. This ability to proliferate can yield millions of stem cells over several months.
• Embryonic stem cells are a particular type of stem cell found in embryos between fertilization and the eighth week of gestation.
• As the embryo develops, these stem cells differentiate and specialize and become all different kinds of cells and tissues.
•Umbilical cord blood is blood that remains in the placenta and in the attached umbilical cord after childbirth.
•Cord blood is collected because it contains embryonic stem cells, which could be used to treat genetic disorders and potentially other illnesses.
•Cord blood is stored by both private and public cord blood banks.
CLONING
What is Cloning?
1. Cloning is the production of genetically identical cells from a single cell.
2. It is easy to clone single cell organisms.
3. Multicellular organisms more difficult to clone.
4. A twin is a natural clone.
Dolly the Sheep
Born: July 5, 1996
Died: February 14, 2003
Place: Edinburgh, Scotland
•Dolly was the first mammal cloned from an adult body cell using the process of nuclear transfer.
•She lived until the age of six and then passed away from lung cancer.
How to Clone a Sheep!
How to Clone a Frog!
Cloning
1. A body cell is taken from a donor animal.2. An egg cell is taken from a second donor animal.3. The nucleus is removed from the egg.4.The body cell and egg are fused by electric shock.
6. The embryo is implanted into the uterus of a foster mother.
5. The fused cell begins dividing, becoming an embryo.
7. The embryo develops into a cloned animal.
1. Save endangered species by storing DNA and cloning
2. Make multiple copies of a useful gene (insulin for diabetics)
3. Clone spare parts, like organs or bone marrow
4. Create experimental groups for studying (animals)
5. Clone "special" animals, pets or horses
How Can Cloning Be Useful?
