Human Cerotype

Punnett Squares

How to predict traits in offspring

Important Vocabulary

1. Homozygous – when you have two of the same genes for a particular trait

a. You are PUREBRED (2 dominant or 2 recessive)

b. TT (tall) tt (short) BB (brown eyes)

2. Heterozygous – When you have two different genes for a particular trait

a. You are Hybrid (always 1 dominant and 1 recessive)

b. Tt (tall) Bb (brown eyes)

Homozygous and Heterozygous Practice Problems

T = tall t = shortB = brown eyes b = blue eyes

1. Homozygous tall: _________________2. Homozygous short: _______________3. Heterozygous tall: ________________4. Homozygous brown eyes: __________5. Heterozygous brown eyes: _________6. Homozygous blue eyes: ___________

Bikini Bottom Genetics

1. For each genotype below, indicate whether it is heterozygous (He) or homozygous (Ho)

TT ____ Bb ____ DD ____ Ff ____Tt ____ tt _____ dd ____ Dd ____BB ____ FF ____ ff _____ bb _____

2. Which of the genotypes would be considered purebred? _______________________________________________

3. Which of the genotypes would be considered hybrids? ________________________________________________

Punnett Squares

1. Punnett Squares – a grid showing genetic material

- Shows probability, not actual results- Uses percentage to predict what might

happen to the offspring- 0 %, 25%, 50%, 75% or

100%

Punnett Square Problems

T = tall t = short

1. A heterozygous tall man has children with a homozygous short women.

1. Write down the genotypes of the parents

Father = _________

Mother = _________

Tttt

Step 1 – Draw a box and put a line going down and across

Step 2 – Put Mother’s genes on top of box and father’s on left hand side

t t

T

t

Step 3 – bring letters down and across

Completed Punnett Square

End result:

_____ tall

_____ shortTt Tt

tt tt

tt

Tt

t t

T

t

50 %50 %

B = brown eyes b = blue eyes A father is homozygous for brown eyes and the mother is homozygous for blue eyes. What is the expected outcome?

Father = ______

Mother = ______

BB

bb b b

B

B B b

B b

B b

B b

____ % heterozygous

____ %

homozygous

100

0

G = Green pea g = yellow peaA heterozygous green pea plant is crossed with homozygous green pea plant. What is the expected outcome?

Plant 1 = ______

Plant 2 = ______

Gg

GG G g

G

G GG

GG

G g

Gg

____ % heterozygous

____ %

homozygous

50

50

T = tall t = short A mother and father are both heterozygous for being tall.

Father = ______

Mother = ______

Tt

Tt T t

t

T T T

T t

T t

t t

____ % tall

____ % short

75

25

C = curly hair c = straight hair A dog that is purebred for straight hair is bred with a dog that is hybrid for curly hair.

Dog 1 = ______

Dog 2 = ______

cc

Cc c c

c

C Cc

c c

C c

c c

____ % purebred

____ % hybrid

50

50

How to Make a Punnett Square.

1. Draw a square and divide it into 4 sections.

2. Write the genotypes for one parent on the top and one down the side.

3. Fill in the sections with one allele from top and one from the side.

4. Figure out the percentages (each box is worth 25%)

Try making your own P-square!

Incomplete Dominance

• There’s always an exception to the rule!

• Genes are the same way. There are times when a blending of the genes occur.

• Skin color or Flower color often does this.

WHITERED

AND

PINK

Word Definition Picture

Incomplete Dominance

When two traits blend

RED A

ND

PINK