Life Science - Chamblee Middle School

Life Science - Chamblee Middle School

Life Science Genetics 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 1800s Mendel noted that the size of pea plants varied. He cross-bred these pea plants to find some surprising results. Mendels cross between tall pea plants yielded all tall pea plants. His cross between small pea plants

yielded all small pea plants. X = 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 = Mendels 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 DNA is found in all living cells

It controls all functions inside a cell It stores all the genetic information for an entire living organism Single cell like an amoeba Multi cell like a human 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 its 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 isnt 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 doesnt, 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 Homozygous dominant Ww - has a widows peak Heterozygous ww - no widows peak 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 recessive Either Ww or WW Homozygous 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 x 2 Assume Lilly is heterozygous Ww Assume Herman is homoozygous recessive ww One gene is called an allele W

w w Ww ww 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

a widows peak Half ww, Homozygous, and have a widows peak have Wwill not w w Ww ww

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 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

W W w Ww ww w Ww Ww

w Ww ww w Ww Ww Genetics If Lilly were heterozygous, then 1/2 of their offspring

should have a widows peak, 1 /2 shouldnt If Lilly were homozygous, all of their children will have a widows peak W w W

W w Ww ww w Ww Ww 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 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. + 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)

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