Genetics Chapter 3C

This section will introduce

heredity- the way traits are passed

from parents to offspring. You will

explore how crosses between

different parents produce different

offspring. You will distinguish

between genotype and phenotype

and use math to predict the results

of genetic crosses.

Think About It:

Observe the three children in the picture:

Make a list of characteristics that

you observe about these children.

Video Clip: Genetics: What are Genes?

1. Inside almost every cell is a nucleus

containing _________ of your genes.

2. In total, you have nearly ________ genes.

3. Your genes are small parts of a long

molecule called ______.

4. Genes tell a cell how to _____________ and

what _____________________ to express.

5. Humans have _________ chromosomes; two

sets of ____________ or ____________ pairs.

Video Clip: Genetics: What are Genes?

1. Inside almost every cell is a nucleus

containing 99.9 % of your genes.

2. In total, you have nearly 20,000 genes.

3. Your genes are small parts of a long

molecule called DNA.

4. Genes tell a cell how to function and

what traits to express.

5. Humans have 46 chromosomes; two

sets of 23 or 23 pairs.

HEREDITY p.2

• Heredity = the passing

of traits from parent to

offspring

• Traits are controlled by

genes; so therefore, the

study of how traits are

inherited or passed

from generation to

generation is called

GENETICS.

GENETICS TREE

• Each person will

be given a leaf for

the genetics tree.

• Females will be

represented with a

pink leaf, males

with a blue leaf.

Earlobes

If earlobes hang free, they are detached. If they attach directly to the side of the head, they are attached earlobes. The size and appearance of the lobes are also inherited traits.

Free Attached

Handedness

Tongue Rolling

In 1940, the famous geneticist Alfred Sturtevant

noted that about 70% of people of European

ancestry are able to roll up the lateral edges of the

tongue, while the remaining 30% were unable to do

so.

1. What is the most common

combination of traits in the

class?

2. What is the least common

combination of traits in the

class?

1. What is the most common

combination of traits in the

class?

free earlobes

right handed

tongue roller

2. What is the least common

combination of traits in the

class?

attached earlobes

left handed

non tongue roller

THE GENE WHEEL p.2

• Each of us has a variety of traits (or

characteristics) that makes us unique and

creates a diverse population.

• One way to see our similarities and

differences is to complete a genetic wheel

and look at the final genetic number.

• This number doesn’t have a particular value

other than to show how you’re different from

someone else.

THE GENE WHEEL p. 2

• Where are you in the Gene Wheel?

• In the chart, start by numbering all around the wheel from 1 to 32.

• Start in the middle and shade in the box for either right handed or left handed.

• Work outward.

• What is your Gene Wheel number?

Double jointed!

Long 2nd Toe!

Heredity Questionnaire

What makes you unique? The combination of genes you

got from your mom and dad determined many things about

you, from the color of your eyes to the size of your feet.

But the music you listen to, foods you like, things you

learn, and other life experiences are just as important in

making you unique!

Gender

Hair Color

Wavy

»

»

» St

Straight

Curly

Hair Texture

Cowlick

Widow’s Peak

Eye Color

Complexion

Eye Dominance

Colorblindness is due to a recessive allele located on the X

chromosome. Women have two X chromosomes, one of which usually

carries the allele for normal color vision. Therefore, few women are

colorblind. Men only have one X chromosome, so if they carry the

allele for colorblindness, they will exhibit this trait. Thus,

colorblindness is seen more frequently in men than in women.

Color Blindness

Ear Lobes

Free Attached

This trait is reportedly due to a single gene;

the presence of freckles is dominant, the

absence of freckles is recessive.

Freckles

Dimples

Dimples are reportedly due to a single gene

with dimples dominant (people may exhibit a

dimple on only one side of the face) and a lack

of dimples recessive.

Can You?

Or Can’t You?

Tongue Roll

Tongue Can Touch Nose

Handedness

Hitchhiker's Thumb Regular Thumb

Hitchhiker’s Thumb

Hands Clasped

One study found that 55% of people place their left thumb on top, 45% place their right thumb on top and 1% have no preference.

Thumbs Folded

Arms Folded

Hair on Fingers

Mid-digital hair – this is hair on the middle knuckle

of your fingers, it is tiny and usually it’s easier to see

the dots it grows out of than the hair itself. Check the

fourth finger as it’s the most common. Having hair is

dominant.

Cleft Chin

GREGOR MENDEL p.9

o First known geneticist and “father of genetics”

o Was an Austrian monk and was born in 1822

o Did most of his genetic studies on pea plants

o He made careful observations, and strictly adhered to the scientific method

o He performed cross-

pollination by

becoming the

pollinator himself,

and controlling which

plants mixed.

o Some traits Mendel

worked with were the

shape of pea and it’s

pod, color and shape

of seeds, plant height,

flower position and

flower color.

GENOTYPE AND PHENOTYPE In humans, one allele is inherited from ones

biological father and one allele from ones

biological mother for each genetic trait.

The genetic structure is called the genotype.

The outward appearance is the phenotype.

Think about it:

Suppose you wanted to know if two Labrador

dogs with black fur could together have

brown puppies. You couldn’t tell by looking at

them.

What they actually look like is the phenotype.

But if you read their genotype- the genetic

code that they inherited from their parents- you

could tell if brown puppies is a possibility.

What are some examples of phenotypes?

Take for example someone

who inherits R (can roll

tongue) from their mother

and r (cannot roll tongue)

from their father. Their

genotype is Rr.

Another individual inherits an

R from both their mother and

their father. What is the

genotype? ____

Take for example someone

who inherits R (can roll

tongue) from their mother

and r (cannot roll tongue)

from their father. Their

genotype is Rr.

Another individual inherits an

R from both their mother and

their father. What is the

genotype? RR

DOMINANT AND RECESSIVE p.10

Write a definition

for the word

dominate

DOMINANT AND RECESSIVE p.10

Genes can either be dominant or recessive.

• Red potato skin is dominant over white potato skin

DOMINANT AND RECESSIVE p.10

Genes can either be dominant or recessive.

• Green peas are dominant over yellow peas

DOMINANT AND RECESSIVE p.10

Genes can either be dominant or recessive.

• Tall sunflower plants are dominant over short sunflower plants

ROCK, PAPER, SCISSORS

Possible Outcomes

• Rock dominates scissors.

• Scissors dominates paper.

• Paper dominates rock.

Conclusion Questions

1. Which outcome was most common in

your partnership?

2. Which outcome was least common?

3. Were your results similar to the result of

the class?

4. Describe one thing you learned about

genetics by doing this activity.

DOMINANT AND RECESSIVE p. 11

A dominant trait is always represented

with a capital letter.

A recessive trait is always represented

with a lowercase letter.

Example:

R= dominant r = recessive

Example:

Hand cross left thumb on top (dominant) T

Hand cross right thumb on top (recessive) t

T

T

TT

T

t

cross with left thumb

on top Tt

If a person inherits a recessive trait from the mother _________ and the recessive trait from the father __________ the person will _________________________ ______________or ________ .

t

t

tt cross with right thumb

on top

o A dominant trait

will always be

expressed and will

mask a recessive

trait.

o A recessive trait

can only be

expressed if there

are no dominant

alleles present.

Example: Eyecolor—Brown color is dominant and blue is recessive.

A person can have a brown allele and a blue allele but still have brown eyes because the brown allele is dominant and “hides” the blue allele.

Circle the picture for the dominant

trait. Then record all of the

possible outcomes.

Widow’s Peak (w) ________

No widow’s peak (W) ________

Circle the picture for the dominant

trait. Then record all of the

possible outcomes.

Widow’s Peak (w) ________

No widow’s peak (W) ________

Circle the picture for the dominant

trait. Then record all of the

possible outcomes.

Widow’s Peak (w) ww

No widow’s peak (W) WW, Ww

Each

organism is

represented

by TWO

letters, one

for each

allele.

HOMOZYGOUS AND HETEROZYGOUS p. 12

The dominant or

recessive

combinations

are called either

homozygous or

heterozygous.

Homozygous:

have identical alleles for a single trait.

Example: RR

rr

• These genotypes are considered

purebred.

• These species have two alleles of the

same trait, and therefore would be

represented by two of the same letters.

Heterozygous:

2 different alleles for a single trait.

Example: Rr

• These genotypes are considered hybrid.

• Species with two different alleles or two different forms of the gene would have two different letters and be called heterozygous.

Let’s Practice:

Determine the genotypes for each

using the information in the chart

below.

T = Tall t = short

B = Brown b = blue

L = Long l = short

T = Tall t = short

B = Brown b = blue

L = Long l = short

TT

tt

Tt

BB

Bb

T = Tall t = short

B = Brown b = blue

L = Long l = short

bb

LL

Ll

LL, Ll

BB, Bb

Genetics Practice Problems p. 13

Ho

He

He

Ho

Ho

Ho

He

He

Genetics Practice Problems p. 13

He

He He

He

Ho

Ho

Ho

Ho

Genetics Practice Problems p. 13

purple

purple

white

Genetics Practice Problems p. 13

blue

brown

brown

Genetics Practice Problems p. 13

wrinkled

round

round

Genetics Practice Problems p. 13

No bobtail

No bobtail

bobtail

Genetics Practice Problems p. 13

SS

Ss

ss

Genetics Practice Problems p. 13

PP

Pp

pp

Generations of Traits p. 9

Each person in

class has a

unique

combination of

traits or

observable

characteristics!

• Why do children often resemble their siblings and parents?

• In this activity you will track and record the passage of colored pom-pom “traits” through three generations of gingerbread people.

black

Punnett Squares p. 14

An Englishman named Punnett figured out an easy way to predict the possible appearance of certain hereditary traits. Use the Punnett Squares below to predict the results of various crosses between pea plants.

Example: Tall plants (T) are dominant to short plants (t)

cross

Example: Tall plants (T) are dominant to short plants (t)

cross

Example: Tall plants (T) are dominant to short plants (t)

TT = Tall

tt = Short

Example: Tall plants (T) are dominant to short plants (t)

Make sure

you can tell

your capital

letters from

your

lowercase

letters.

Example: Tall plants (T) are dominant to short plants (t)

Think about

money and

quarters

when

determining

percentages.

0

100

0

100

0

A. Tall plants (T) are dominant to short plants (t)

T t

T

t

TT Tt

Tt = Tall

Tt = Tall

A. Tall plants (T) are dominant to short plants (t)

25

50

25

75

T t

T

t

TT

tt Tt

Tt

A capital letter

will always

come first

because it is

dominant.

25

A. Tall plants (T) are dominant to short plants (t)

25

50

25

100

T t

T

t

TT

tt Tt

Tt

25

Short is a

possibility

because each

parent carries

the recessive

gene.

B. Tall plants (T) are dominant to short plants (t)

T T

T

t

Tt = Tall

TT = Tall

B. Tall plants (T) are dominant to short plants (t)

T T

T

t

Are short

plants

possible? TT

Tt Tt

TT

50

50

0

100

0

No!

B. Tall plants (T) are dominant to short plants (t)

T T

T

t

What would

have to

happen in

order for

short plants

to be a

possibility?

TT

Tt Tt

TT

50

50

0

100

0

B. Tall plants (T) are dominant to short plants (t)

T T

T

t

TT

Tt Tt

TT

50

50

0

100

0

Each parent

would have

to carry the

recessive

gene (t)!

PUNNETT

SQUARE

PRACTICE

p. 15

1. Predict the fur color of the offspring of a brown heterozygous

hamster and a white homozygous hamster.

Use B: Brown is dominant. White is recessive.

BB

bb

Bb

brown

brown

white

B

b

b b

Bb

bb bb

Bb 50

50

2. Predict the offspring of 2 gray heterozygous rats.

Use G: Gray is dominant over white.

GG

gg

Gg

gray

gray

white

G

g

G g

GG

gg Gg

Gg 75

25

3. Predict the pea shape of the offspring of one heterozygous

round pea plant and one homozygous wrinkled pea plant.

Use P: Round is dominant over wrinkled.

PP

pp

Pp

round

round

wrinkled

P

p

p p

Pp

pp pp

Pp 50

50

4. Are the chances greater for having a boy or a girl?

_______ = female and ________ = male

PP

pp

Pp

round

round

wrinkled

X

X

X Y

XX

XY XX

XY 50

50

XX XY

XX

XY

girl

boy