predicting inheritance using punnett squares

23
Predicting Inheritance using Punnett Squares Unit 5: Genetics Chapter 11-2

Upload: melosa

Post on 24-Feb-2016

42 views

Category:

Documents


0 download

DESCRIPTION

Predicting Inheritance using Punnett Squares. Unit 5: Genetics Chapter 11-2. Let’s Review our Vocab !. Dominant traits cover up Recessive traits Dominant Allele = capital letter (B) Recessive Allele = lower case letter ( b ). P = Parents. F1 = first generation offspring. - PowerPoint PPT Presentation

TRANSCRIPT

Predicting Inheritance using Punnett Squares

Unit 5: GeneticsChapter 11-2

• Dominant traits cover up Recessive traits– Dominant Allele = capital letter (B)– Recessive Allele = lower case letter (b)

Let’s Review our Vocab!

P = Parents

F1 = first generation offspring

F2 = second generation offspring

• B=Black b=white– Bb: Dom or Rec? Color?

• T=Tall t= short– TT: Dom or Rec? Height?

• P=Purple p=white– pp?: Dom or Rec? Color?

Dominant or Recessive?

• Genotype: the actual alleles for a trait • Represented by letters: AA, aa, Aa

– Homozygous Dominant: 2 dominant alleles (AA) (purebred)

– Homozygous Recessive: 2 recessive alleles (aa) (purebred)

– Heterozygous: 1 dominant allele & 1 recessive allele (Aa) (hybrid)

Homozygous or Heterozygous?

• BB• Kk• ff

Purebred or Hybrid?• rr• Ww• NN

• Homozygous dominant• Heterozygous• Homozygous recessive

• purebred• hybrid• purbred

• Phenotype: how the trait is seen – Ex: Guinae pig fur color: black or white

P = Parents

F1 = first generation offspring

F2 = second generation offspring

Genotype or Phenotype?

• Black• Bb• tt• Short• KK• Pp• Tall• White

• Phenotype• Genotype• Genotype• Phenotype• Genotype• Genotype• Phenotype• Phenotype

Punnett Squares

• Used to predict the traits of each possible offspring during a cross

• Five Step Plan– 1) Legend– 2) Parents– 3) Punnett square-set it up– 4) Punett square-fill it in– 5) Answers in boxes

5-Step Plan for Punnett Squares Flee Map

1) Legend 2) Parents 3) Punnett Square: Set it up

4) Punnett Square: Fill it in

5) Answers

Pg 10

5-Step Plan

Sample ProblemYou do NOT have to write this slide!

• In guinea pigs, Black (B) is dominant to White (b)• Black guinea pig (BB) x White guinea pig (bb)

• What are the chances that the offspring will be black? White?

• How many offspring will be black? How many will be white?

Five-Step Plan• 1) Legend

– Always use the first letter of the dominant trait to represent your alleles. (ex: in this case, we use B for black)

– Set up a table: Genotype Phenotype

BB

Bb

bb

Black

Black

White

• 2) Parents - Write this as a “cross”

– BB x bb

• 3) Punnett Square - Set it up– Draw a square and divide into four sections– Write the genotype (letters) from one parent on

top (one letter per box) – Write the genotype from the other parent along

the left side B

Bb

b

• 4) Punnett Square - Fill it in– Fill in the boxes with one letter from the top and

one letter from the left (2 letters per box)

BB

b

b

B

B

B

B

b

b

b

b

• 5) Answers– Each box = a 25% chance of offspring inheriting

that genotype– Always put a box around your final answer!!!

BB

b

b

B

B

B

B

b

b

b

b

100% Black offspring0% White offspringRatio: 4 : 0 OR 1 : 0 (Black : White)

• Now we have COMPLETELY answered the question and we are done!– Always double check!

Now you practice on the

whiteboard!

Whiteboards

• Keep your notes & flow map in front of you. • Please do not draw on whiteboard unless

instructed.• For each problem you will do steps 1 & 2

(legend & parents) first.• You will then do steps 3-5 (Punnett square and

answers).

Example:Purple Flower (PP) x White Flower (pp)

P P

p

p

What % of the offspring will be Purple? White?

What is the ratio of purple : white? (Hint: how many of each & reduce)

Pp Pp

PpPp

100 % Purple0% White

1: 0

Example:Tall (Tt) x short (tt)

t t

T

t

What % of the offspring will be Tall? Short?

What is the ratio of tall : short? (Hint: how many of each & reduce)

Tt Tt

tttt

50 % Tall50% Short

1: 1

Example:Brown eyes (Bb) x Brown eyes (Bb)

B b

B

b

What % of the offspring will be Brown eyes? Blue eyes?

What is the ratio of brown eyes : blue eyes? (Hint: how many of each)

BB Bb

bbBb

75 % Brown25% Blue

3: 1

Example:Dimples (DD) x No Dimples (dd)

D D

d

d

What % of the offspring will have dimples? No dimples?

What is the ratio of dimples : no dimples? (Hint: how many of each & reduce)

Dd Dd

DdDd

100 % Dimples0% No dimples

1: 0

Normal thumbs (T) are dominant to hitchiker’s thumbs (t). A man with hitchiker’s thumb marries

a women that is heterozygous for a normal thumb.

t t

T

t

% of Normal thumbs? % Hitchiker’s thumbs?

Ratio?

Tt Tt

tttt

50 % Normal50% Hitchiker’s

1: 1

Free earlobes (F) are dominant to attached earlobes (f). A man with attached earlobes

marries a women that is homozygous for free earlobes.

f f

F

F

% Free Earlobes? % Attached earlobes?

Ratio?

Ff Ff

FfFf

100 % Free0% Attached

1: 0