6th grade chapter 4

Chapter 4

Heredity and Reproduction

Continuing Lifesection 4-1 HW. Pg 99 ques. 1-4

• Millions of different kinds of things inhabit our Earth. And new organisms are the result of a process called reproduction.

• Reproduction is important to all living things because without it, a particular species would not be able to continue.

Cell Division• During reproduction, genetic

information is passed from parent to offspring.

• This genetic information is contained in a chemical called DNA and is found in the nucleus of cells.

• DNA controls what the new offspring will look like as well as how their bodies and cells work.

Cell Division• We all know that you were not born

the size that you are now. And two years ago you were not the size you are now.

• So how is it that you grew from the size of a baby to the size that you are now.

• You are able to grow and develop by a process called mitosis, the process in which one cell splits its nuclei and its DNA to produce two exact genetic copies of itself.

Cell Division• Another name for mitosis is cell

division.• So now we know that new cells come

from other cells.• One important fact to now here is

that before mitosis occurs the DNA inside the chromosomes of the parent cell is copied so that when the cell splits, each cell has equal amounts of the parent DNA.

Cell Division

• Cells go through mitosis in order to assure that each new cell receives exactly the same information as the cell it came from.

• Also, cells go through mitosis in order to grow and replace dead or damaged cells, like when you get a cut, or break a bone.

5 Stages of Mitosis.• Mitosis occurs in 5 stages, and they

are called:1) Interphase2) Prophase3) Metaphase4) Anaphase 5) Telophase

5 Stages of Mitosis.1) Interphase- What happens here is

the chromosomes inside the nucleus are duplicated.

2) Prophase- Here, the chromosomes become visable and the spindle apparatus, which is used to separate the chromosomes is formed.

5 Stages of Mitosis.

• Interphase and Prophase pics.

5 Stages of Mitosis.3) Metaphase- The chromosomes line

up in the middle of the cell and begin to be pulled apart from one another.

4) Anaphase- In anaphase all of the chromosomes that were lined up in the middle of the cell are completely pulled apart from on another.

This leaves two sets of equal numbers of chromosomes on each end of the cell.

5 Stages of Mitosis.

• Metaphase and Anaphase pics.

5 Stages of Mitosis.

5) Telephase- here the cell wall pinches in and the cells divide into two cells of equal size.

Pic of Telophase

Reproduction from one parent.• The method in which an organism can

produce a new organism from one parent is called, what?

• Asexual reproduction• In asexual reproduction, all the DNA in

the new organism comes from only one parent.

• A potato uses asexual reproduction, so every potato that comes from one parent potato will have the same DNA as that parent.

There are 2 ways in which reproduction from one parent

occurs.

1) By Splitting-bacteria and other single celled organisms divide in half, forming two new cells.

When the cell divides, each new cell gets an exact copy of the parents DNA.

Now the two new cells are exactly alike and the parent cell no longer exists.

There are 2 ways in which reproduction from one parent

occurs.

2) Budding out and breaking up- Many mushrooms, plants, and some animals use budding as a form of asexual reproduction.

Here a new cell will bud off of the parent cell, break away and live on its own.

• Some species of organisms, a whole individual can grow from just a part of a parent organism.

• Ex: If you cut a piece of ivy, that piece that you cut can be planted and grow to a new plant.

• In a process called regeneration some organisms are able to replace body parts that have been lost because of injury.

Sexual Reproduction• In sexual reproduction- a new organism is

produced from two parents.• During this process, DNA from both

parents combine to form a new individual with its own DNA.

• In Chapter 3 we spoke of how there are different cells for different function in the human body.

• For sexual reproduction have cells called sex cells.

Sex cells

• There are two types of sex cells:1) Sperm- a male sex cell2) Ova or egg- a female sex cell.

Normal or non sex cells in your body have 46 chromosomes, and when they divide the new cells gets all 46 chromosomes that the original had, and we said that this process was called mitosis.

Sex Cells

• Sex cells are a little different. They go through a process called meiosis, which is the formation of sex cells.

• Sex cells only contain 23 chromosomes, which is half the amount that a normal non-sex cell would have.

• So when they divide only 23 chromosomes are given to the new cell.

Sex Cells

• So, each sperm and egg have 23 chromosomes and when they join in a process called fertilization, the result or offspring has a full set of 46 chromosomes.

Seed Production• Flowers also reproduce and have

reproductive structures. • Male flower parts produce pollen,

which contains sperm cells.• Female flower parts produce eggs and

when the sperm and egg meet a new cell forms.

• As this new cell develops it becomes enclosed in a seed, which protects it and helps to keep it alive.

Cloning• Cloning- creating an organism that

has exactly the same DNA as another organism.

• Scientists sometimes call cloning embryo splitting.

• An embryo is a fertilized egg that has begun dividing into more cells.

• A clone receives all of its DNA from just one parent.

Cloning

• The first mammal that was successfully cloned was a sheep called Dolly in 1997.

• Dolly grew from a single cell from another sheep. She did not have 2 parents.

• Through this experiment scientists learned a great deal about how cells work.

Cloning

• They learned how a single cell can develop into an entirely new organism with skin cells, bone cells and other body cells.

• Scientists think that through this technology it might be possible to grow different types of cells such as nerve and muscle cells in the laboratory.

GeneticsSection 4-3 H.W. pg 111 ques. 1-4 & pg 114 ques. 1-10

• Did you ever notice that you and your family members share a lot of physical similarities.

• That’s because of something called heredity.

• Heredity- this is the passing on of traits from a parent to an offspring.

Genetics• What makes you different from the

person next to you is the types of traits that were given to you by your parents.

• We said that traits were specific features of something. And every organism has its own unique collection of traits.

• The study of how traits are passed from parent to offspring is called genetics.

Genes on Chromosomes• So we know that your DNA makes up

your genetics and that your DNA makes up your chromosomes.

• Half of the information on your chromosomes came from your mother and the other half comes from your father.

• This information was contained in chromosomes inside of sex cells that combined to eventually form you

Genes on Chromosomes• How to chromosomes work? • Well all chromosomes contain genes, a

small section of chromosome that determines a specific trait.

• Genes are arranged on chromosomes one next to another.

• These genes control all of the traits of organisms, even the ones that cant be seen.

• Genes provide all the information needed for the growth and life of that species.

DNA• We said that DNA is our genetic

material that makes us who we are. • Also we learned that DNA is what makes

up our chromosomes.• DNA is contained in the nucleus of all

cells and is called our genetic information.

• DNA is kind of like a blue print that contains all of the instructions for how an organism looks and functions.

• DNA controls the color and texture of your hair, the shape of your ears and even how you digest food.

Alleles • We learned that chromosomes in non

sex cells come in pairs and the same is true for the genes on those chromosomes.

• One single gene that makes a trait is made of 2 alleles. Each allele contributes to that trait.

• The combination of these alleles determines how a trait will be shown.

• Your gene that gives you your hair color is made of 2 alleles. If you have 2 alleles that cause black hair than you will have black hair. What would happen if you had one allele for black hair and one for blonde hair, what color would your hair be?

Alleles• Your hair would be black.• This is because of something called

dominance and recessives. • Dominance means that one trait will be

expressed over another.• An example of excessiveness would be

the allele that is not seen or expressed. Here it was our blonde hair allele.

• When an organism has two identical alleles for a trait that organism is said to be pure.

• If it has two alleles that are different then its called a hybrid.

Passing Traits to Offspring

• How are your parents traits or your grandparents traits passed on to you?

• You inherit traits based on the genes of your parents. And the same holds true for every organism.

• Depending on if your parents are pure or hybrids all depend on the trait that you will show.

Punnett Square

• When your parents sex cells join together they combine alleles. When these alleles join they determine what trait will be expressed.

• Using a Punnett square we are able to determine the chances of the expression of traits shown by offspring.

Punnett Square

Differences in Organisms

• We now know why we have similar traits and features of our parents.

• Because we inherited their genes and their genes will determine our eye color, skin color, hair color etc…….

• But why are there still some differences or variations.

• Variations are the different ways a certain trait appears. Like height.

Multiple Genes and Multiple Alleles.

• This variance in traits is do to multiple genes and multiple alleles.

• Our blood type is determined by more than two alleles.

• Our eye color and hair color is determined by several genes.

• Since you need more genes or alleles to determine certain traits that causes a larger variance in traits.

Mutations• Mutations are another source of trait variation.• A mutation is a change in a gene or a

chromosome due to some error during cell division.

• Some mutations could be caused from outside sources like UV light from the sun or smoking.

• Some mutations occur because they are present on the parent DNA and it is passed down to the offspring.

• Not all mutations are of the negative variety. Some are good. Like a 4 leaf clover. Normally it will have 3 leaves but due to a mutation it has 4. This is good because the extra leaf can trap more sunlight for photosynthesis.

Test on Chapter 4 in one Week!!!!!