S7L3

S7L3• Students will recognize how biological traits are passed

on to successive generations.

• a. Explain the role of genes and chromosomes in the process of inheriting a specific trait.

• b. Compare and contrast that organisms reproduce asexually and sexually (bacteria, protists, fungi, plants & animals).

• c. Recognize that selective breeding can produce plants or animals with desired traits

1. What do we call different forms a gene may have for a trait?

2. What height of pea plant (tall or short) did Mendel find to be dominant?

3. How are dominant and recessive traits represented? (upper or lower case)

Give an example!

• HeredityHeredity : the passing of traits from

parent to offspringparent to offspring

Traits are controlled by genes genes, SO what is GENETICS?

Genetics: The study of how

traits are inheritedinherited.

GREGOR MENDELGREGOR MENDELo First known geneticist and

“father father of genetics”

o Was an Austrian monk and was born in 18221822

o Did most of his genetic studies on peapea plants

o He performed cross-pollinationo He became the pollinatorpollinator himselfo He controlled which plants mixed.

o Some traits Mendel worked with were shapeshape of pea pea and it’s pod, colorcolor and shape of seedsseeds, plant heightheight, flower positionposition and flower color.

WHAT ARE ALLELES?WHAT ARE ALLELES?o Are ONE FORM FORM of a gene (there can be

more than one form)

o Body cells have two two forms or ALLELES for a single gene (you got one from Mom and one from Dad)

o One may be dominantdominant over another. If this happens, the dominant gene is the one expressed. If not, the recessive trait is expressed.

DOMINANT AND RECESSIVEDOMINANT AND RECESSIVE

o A Dominant trait: will always be expressed and will “maskmask”

or hide a recessive trait

o A recessive trait can only be expressed if there are no dominant dominant alleles present.

ExampleExample: Eyecolor—Brown color is dominantdominant

and blue is recessive. A person can have a brown allele and

a blue allele but still have brownbrown eyes because the brown allele is dominant and “hideshides” the blue allele.

Example:RR= dominant rr = recessive

• Generally, dominant alleles are represented with a capitalcapital letter, and recessive alleles are represented with a lower caselower case letter.

Each gene is

represented by TWOTWO

letters, one for each allele.

o “Purebred” species have two alleles of the same same traito Represented by two of the same letters.

This is called homozygoushomozygous. For instance: For instance: BB or bb.BB or bb.

o Species with two different alleles or two different forms of the gene would be “hybrid”o Represented by two different “lettersletters” and

by called “heterozygous”. For instance: BbFor instance: Bb

o The alleles present in the organism are referred to as its genotypegenotype. For instance, BB, Bb, or bb.BB, Bb, or bb.

o The PHYSICALPHYSICAL trait that shows, regardless of genotype is called a PHENOTYPEPHENOTYPE.

o For instance, BlueBlue or BrownBrown Eyes.

Mom has blue eyes (bb)

Dad has brown eyes (BB or Bb)

Daughter has blue eyes (bb)

Therefore, Dad must have the Bb genotype, because he must have given her the “b” allele. His “b” allele is masked by his “B”/dominant allele.

Genetics by Brainpop

http://www.brainpop.com/health/seeall

PROBABILITYPROBABILITY

o Helps predict the chance chance that something will happen

o ExampleExample: the probability of throwing heads or tails on a coin is 50% 50% (1/2 chances)

o Your predictions become more accurateaccurate with the more trials you run!

Using a Punnett Square…Using a Punnett Square…

o Used to help predict Mendelian genetics

Steps for using the Punnett square:

1) One parent’s alleles (genotype) (genotype) go along the top

2) The other parent’s alleles go down the side.

3) You fill in the squares like doing the communicative property of multiplication.

B b

B

b

BB

bbBb

Bb

Steps for using the Punnett square:Steps for using the Punnett square:

Let’s say the parents are Bb and Bb (the same

genotype). What would be their phenotype?

Brown EyesBrown EyesB b

B

b

So you would predict:

¼ offspring to be BB, or Brown Eyes

2/4 or 1/21/2 to be Bb, or BrownBrown Eyes

and ¼ to be bb or BlueBlue eyes

BB

bbBb

Bb

So, if Miss Hemphill had children with her husband to be …what color eyes would they have?

Mr. Ellinger

Blue eyes (bb)

Miss Hemphill

Blue eyes (bb)

All of their kids would have blue eyes!

bb bb

bb bb

b b

b

b

Using a Punnett Square Clip

Let’s try some practice Let’s try some practice problems…problems…

Practice Problem #1Practice Problem #1

• Predict the fur color of the offspring of a brown heterozygous

hamsters and a white homozygous hamster. Brown is dominant. White is recessive.

• Use any letter you like.


Bb bbBb bb

B b

bb


• Predict the offspring of 2 white homozygous cows. Black is dominant over white.



bb bbbb bb

b b

bb


• Predict the offspring of 2 Grey Heterozygous rats. Gray is dominant over white, which is recessive.



GG GgGg gg

G g

Gg


• Predict the pea shape of the offspring of one Heterozygous Round Pea plant and one homozygous wrinkled pea plant. Round is dominant over wrinkled.



Rr rrRr rr

R r

rr

Practice Problem #5Practice Problem #5you don’t have to write this one down…you don’t have to write this one down…

• What are the chances of having a boy or a girl?

• How would you solve this one?


XX XYXX XY

X Y

XX

Closing

1. Take out piece of paper and pen/pencil.

2. Put all notes away.

Heredity by Brainpop

Heredity by Brainpop

1What do we call different forms a gene may have for a trait?

2What height of pea plant (tall or short) did Mendel find to be dominant?

3Which kind of trait can’t be passed from parent to child?a)Eye color b) height c) broken arm

S7L3

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