Life ScienceGenetics http people pppst comgregormendel html Asexual

Life Science-Genetics http: //people. pppst. com/gregor-mendel. html

Asexual Reproduction An organism reproduces by making an exact copy of its genetic material and then dividing. The offspring gets all of its traits, or characteristics, from this one organism. Sexual Reproduction An egg cell and a sperm cell unite to form a single cell. This is called fertilization.

Genetics The study of heredity, how traits are passed from parent to offspring x or = or

The study of heredity started with the work of Gregor Mendel and his pea plant garden Mendel was an Austrian Monk that lived in the mid 1800’s

Mendel noted that the size of pea plants varied. He cross-bred these pea plants to find some surprising results.

Mendel’s cross between tall pea plants yielded all tall pea plants. His cross between small pea plants yielded all small pea plants. X = Mendels’ cross between tall pea plants and small pea plants yielded all tall pea plants. x =

Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being small. x =

Mendel’s work led him to the understanding that traits such as plant height are carried in pairs of information not by single sets of information. -Carrying the information are chromosomes. -Chromosomes are made up of sections called genes. -Genes are made up of DNA

DNA D. N. A. - Deoxyribonucleic Acid Molecule made of: 1. Deoxy Sugar 2. Combination of four nitrogen bases Either: a. Guanine b. Cytocine c. Thymine d. Adenine The sum total of combinations that these four bases are capable of creating are greater than all the stars visible in the night time sky

DNA �Nitrogen bases pair up �Cytosine & Guanine �Thymine & Adenine �Pairing creates a ladder shape �Angle of bonds creates a twist Ladder and Twist produces the famous “Double Helix”

DNA Cell �DNA resides in all cells �Inside the nucleus �Each strand forms a chromosome Nucleus DNA

DNA is found in all living cells �It controls all functions cell �It stores all the genetic information for an entire organism � Single cell like an amoeba � Multi cell like a human inside a living

Genetics Small sections of DNA are responsible for a “trait”. These small sections are called “Genes”. �Gene - A segment of DNA that codes for a specific trait �Trait - A characteristic an organism can pass on to it’s offspring through DNA Gene

Genetics Hair color is a perfect example of a trait What color hair should their children have? Prince Charming is blond Snow White has dark hair

Genetics There are three basic kinds of genes: �Dominant - A gene that is always expressed and hides others �Recessive - A gene that is only expressed when a dominant gene isn’t present �Codominant - Genes that work together to produce a third trait

Genetics Dominant and Recessive Genes Widows Peak � A dominant gene will always mask a recessive gene. � A “widows peak” is dominant, not having a widows peak is recessive. � If one parent contributes a gene for a widows peak, and the other parent doesn’t, the offspring will have a widows peak.

Genetics Punnet Square - A tool we use for predicting the traits of an offspring �Letters are used as symbols to designate genes �Capital letters are used for dominant genes �Lower case letters are used for recessive genes �Genes always exist in pairs

Genetics A Widows Peak, dominant, would be symbolized with a capital “W”, while no widows peak, recessive, would be symbolized with a lower case “w”. Father - No Widows Peak - w Mother - Has a Widows Peak - W

Genetics All organisms have two copies of each gene, one contributed by the father, the other contributed by the mother. Homozygous - Two copies of the same gene Heterozygous - Two different genes

Genetics For the widows peak: WW - has a widows peak dominant Ww - has a widows peak ww - no widows peak Homozygous Heterozygous Homozygous recessive

Genetics Since Herman has no widows peak, he must be “ww”, since Lilly has a widows peak she could be either “WW” or “Ww” Definitely ww Either Ww or WW Homozygous recessive Heterozygous Homozygous dominant

Genetics We can use a “Punnet Square” to determine what pairs of genes Lilly has • A Punnet Square begins with a box 2 Assume Lilly is heterozygous Ww Assume Herman is homoozygous recessive ww • One gene is called an “allele” W w w Ww ww • One parents pair is split into alleles on top, the other along the side • Each allele is crossed with the other allele to predict the traits of the offspring

Genetics Notice that when Lilly is crossed with Herman, we would predict that half the offspring would be “Ww”, the other half would be “ww” Half “Ww”, Heterozygous, and will have a widows peak Half “ww”, Homozygous, and will not have a widows peak W w w Ww ww

Genetics Another possibility is that Lilly might be “WW”, homozygous dominant. Assume Lilly is homozygous dominant WW W Assume Herman is homoozygous ww W w Ww Ww Notice that all the offspring are heterozygous and will have a widows peak

Genetics So which is true? Is Lilly homozygous dominant (WW) or is she heterozygous (Ww)? W w Ww ww w Ww Ww

Genetics If Lilly were heterozygous, then 1/2 of their offspring should have a widows peak, 1/ shouldn’t 2 If Lilly were homozygous, all of their children will have a widows peak W w Ww ww w Ww Ww

Genetics Recall that Herman and Lilly had another offspring, Marylin. She had no widows peak, therefore, Lilly must be heterozygous.

Genetics So, back to the original question. What color hair will the offspring of Prince Charming and Snow White have?

Genetics Hair color is different from widows peak, no color is truly dominant. �Brown and blond are the two, true traits �Homozygous conditions produce either brown or blond hair �Heterozygous conditions produce red hair

Genetics For Snow White to have brown hair she must be homozygous dominant, “BB”, a blond Prince Charmin must be homozygous recessive, “bb”. B B b Bb Bb

Genetics All the offspring from Prince Charming and Snow White will therefore be heterozygous, “Bb”, and since hair color is codominant…. . all their children will have red hair. +

A mistake in a chromosome… • A change in the chromosome number will result in serious medical problems. In Down syndrome for example, the serious abnormalities and mental retardation are the result of an extra chromosome number 21. Down syndrome babies have thus 47 chromosomes instead of 46.

Cell Division (Meiosis) 1. A process of cell division where the number of chromasomes is cut in half 2. Occurs in gonads (testes, ovaries, stamens, etc) 3. Makes gametes (sperm, ova, pollen, etc)

Mitosis �Has six stages �In the 1 st stage, each chromosome in the nucleus duplicates itself. (now it has 2 of each of its chromosomes) �During the 2 nd stage, the chromosomes coil and shorten into rodlike structures. At the end of the 2 nd stage, the nuclear membrane dissolves allowing chromosomes into the cytoplasm. �In the 3 rd stage, long fibers help to position the joined chromosomes in the center of the dividing cell.

�During the 4 th stage, the two copies of each chromosome separate. The attached fibers shorten as the members of the chromosome pairs move to opposite ends of the cell. Now the dividing cell has two identical sets of chromosomes, one at either end of the cell. �During the last two stages, chromosomes begin to uncoil, and a nuclear membrane forms around each set of chromosomes. In the center of the cell, the cell membrane starts to form. If it is a plant cell, a cell wall begins to form. The membrane eventually reaches around the cell, dividing it in two. �Each cell has exactly the same DNA. These cells will soon be able to divide on their own by mitosis.