Solving Genetics Problems

SOLVING GENETICS PROBLEMSHonors BiologyUnit 5Powerpoint #2 / Chapter 11

SOLVING GENETICS PROBLEMS

Phenotype: physical appearanceExample: Tall, Short, Blonde, Red, Brown Eyes

Genotype: genes in the DNA (alleles)

Example: TT bb Rr Bb

ALLELE: A VARIETY OF A GENE A gene for hair color could

have the allele: _______ for Brown hair or _______ for Blonde hair

A gene for flower color could have allele: ______for blue flower or ________ for red flower

A gene for height could have the alleles: _______ for tall or _______ for short

Bb

Bb

T t

Dominant: An allele that causes its phenotype if at least 1 is presentExamples: TT, Tt (Tall)

Recessive: An allele that causes a phenotype only when there are 2 allelesExample: tt (short)



Homozygous: organism with 2 identical alleles for a trait (TT or tt)

Heterozygous: organism with 2 different alleles for a trait (Tt)

Homozygous dominant: has 2 dominant alleles (TT)

Homozygous recessive: has 2 recessive alleles (tt)


A B C D E F G H

Plant A: a. Phenotype: b. Genotype:

Tall

TT

A B C D E F G H

Plant B: a. Phenotype: b. Genotype:

short

tt

A B C D E F G H

Plant C: a. Phenotype: b. Genotype:

Tall

Tt

SOLVING GENETICS PROBLEMSGenetics Problems

Goal: to predict the traits of offspring


Goal: to predict the traits of offspring1. Identify trait(s) and assign a letter to

each (capital letter for dominant, lower case letter for recessive)




2. Determine parents’ genotypes




2. Determine parents’ genotypes3. Draw Punnett square and fill in




2. Determine parents’ genotypes3. Draw Punnett square and fill in4. Determine the probabilities for

offspring of each genotype and phenotype

SOLVING GENETICS PROBLEMSExample:In pea plants, the gene for tall height is

dominant to the gene for short height. A short pea plant is cross pollinated with a true breeding tall pea plant.

1. Assign letters: tall = T short = t

2. Parents’ genotypesTrue breeding tall: TT True breeding short = tt

SOLVING GENETICS PROBLEMS3. Draw Punnett Square


t t

T

T


Tt Tt

Tt Tt

t t

T

T

SOLVING GENETICS PROBLEMS4. Calculate probabilitiesTT = _____Tt = ________tt = _________Tall = _________Short = _________ Tt Tt

Tt Tt

t t

T

T

SOLVING GENETICS PROBLEMS4. Calculate probabilities10) TT = 0/4 Tt = 4/4 tt = 0/411) Tall = 4/4 Short = 0/4 Tt Tt

Tt Tt

t t

T

T

IDENTIFY TRAIT(S) AND ASSIGN A LETTER TO EACH (CAPITAL LETTER FOR DOMINANT, LOWER CASE LETTER FOR RECESSIVE)Examples:In guinea pigs, the gene for black fur is dominant to

the gene for white fur.black = ____ white = ____

IDENTIFY TRAIT(S) AND ASSIGN A LETTER TO EACH (CAPITAL LETTER FOR DOMINANT, LOWER CASE LETTER FOR RECESSIVE.Examples:In guinea pigs, the gene for black fur is dominant to

the gene for white fur.

DETERMINE PARENTS’ GENOTYPES.Example:In guinea pigs, the gene for black fur is

dominant to the gene for white fur. A white guinea pig and a hybrid black guinea pig produce 20 offspring. Find the probability of offspring genotypes and phenotypes.

1. Black: ___White: ___2. White guinea pig: ___

Hybrid black guinea pig: ___



1. Black: B White: b2. White guinea pig: ___



dominant to the gene for white fur. A white guinea pig and a hybrid black guinea pig produce 20 offspring. Find the probability of offspring genotypes and phenotypes

1. Black: B White: b2. White guinea pig: bb




1. Black: B White: b2. White guinea pig: bb

Hybrid black guinea pig: Bb

SOLVING GENETIC PROBLEMS

Bb bb

Bb bb

B b

b

b

3. Draw Punnett Square

SOLVING GENETICS PROBLEMS4. Calculate probabilities BB = 0/4Bb = 2/4 (50%)bb = 2/4 (50%)

How many of the babies willProbably be Black = 10How many of the babies willProbably be White = 10

Bb bb

Bb bb

B b

b

b

HUMANS CAN HAVE UNATTACHED EARLOBES (PICTURE A) OR ATTACHED EARLOBES (PICTURE B). ATTACHED EARLOBES ARE DOMINANT. USE THE LETTER ‘E’ TO COMPLETE THE FOLLOWING QUESTIONS.

Ear Lobes

HUMANS CAN HAVE UNATTACHED EARLOBES (PICTURE A) OR ATTACHED EARLOBES (PICTURE B). ATTACHED EARLOBES ARE DOMINANT. USE THE LETTER ‘E’ TO COMPLETE THE FOLLOWING QUESTIONS.

1) A mother is homozygous dominant for ear type and a father is heterozygous:

a) What is the mother’s genotype? ______ Father’s genotype? ____

b) What are their phenotypes? Mother: ___________ Father: _________

EEEe

AttachedAttached

1) A MOTHER IS HOMOZYGOUS DOMINANT FOR EAR TYPE AND A FATHER IS HETEROZYGOUS: Draw a punnett square:

E

E

eE

EE

EE

Ee

Ee

1) A MOTHER IS HOMOZYGOUS DOMINANT FOR EAR TYPE AND A FATHER IS HETEROZYGOUS:

d: What are the chances they will have children that are:

Homozygous Dominant: ____

Heterozygous: ____Homozygous Recessive:

____

E

E

eE

EE

EE

Ee

Ee

50%

50%

0%

TONGUE ROLLING: DOMINANT If a mother can roll her tongue and a father

can not. What do we know about their genes?

TONGUE ROLLING: DOMINANT

If a mother can roll her tongue and a father can not. What do we know about their genes?

Mother: _______Father: _______RR or Rr

rr only

2) B. IF YOU KNOW THAT THEY HAVE 2 CHILDREN, ONE THAT CAN ROLL AND ONE THAT CAN NOT. WILL THAT GIVE YOU MORE INFO ABOUT THE PARENT’S GENOTYPES?

c. Draw a punnett square:

r

r

rR

Rr

Rr

rr

rr

Yes!

TONGUE ROLLING: DOMINANT

d. Which people in the family would be considered hybrids?

e. Are their any genotypes that this mother and father can not produce in their offspring? Why or why not?

Mom and the child that can roll their tongue

Yes, they can not produce a Homozygous Dominant (RR) child because the father only has recessive genes (r) to pass on

CO AND INCOMPLETEDOMINANCE

DEFINITIONS

Co-dominance: Both alleles are dominant and contribute to the phenotype of a heterozygous individual Incomplete

Dominance:One allele is NOT completely dominant over the other

SOLVE THE FOLLOWING CROSSES: CO-DOMINANCE

3. In Cows the trait for coat (fur) color is expressed by R for Red fur and W for white fur. The hybrid of the two is called a Roan color (RW).

a) Describe what you think the Roan cow’s fur will look like:

CO-DOMINANCE

FILL IN THE PUNNETT SQUARE

R

W

R

W RW RW

RW RW

Genotypes Phenotypes

http://www.coloring.ws/t.asp?b=m&t=http://www.coloring.ws/animals/cow5.gif

2. R= RED FURW= WHITE FUR

What do you think a RW cow will look like: ____________________

If the mother cow is homozygous red for fur color. What is her genotype: _____ Phenotype?________________

If the dad is homozygous white for fur color. What is his genotype: _____ Phenotype?________________

What percentage of the offspring will be RW: ______________

Red and White spots

RRRed Fur

WWWhite Fur

100%

http://www.coloring.ws/t.asp?b=m&t=http://www.coloring.ws/animals/cow5.gif

SOLVE THE FOLLOWING CROSSES: CO-DOMINANCE4. In mushrooms there is a gene for

Purple Spots (P) and a gene for Green spots (G). Cross a Homozygous purple with a Homozygous Green.

a) What do you think their offspring will look like? Genotype? Phenotype?

b) What will the genotype and phenotype percentages be in the F2 when you cross two from the F1 generation.

PHENOTYPES

PP GG GP

INCOMPLETE DOMINANCEThe heterozygous (Rr) Does not

look like the Homozygous recessive (rr) or the homozygous dominant (RR).

INCOMPLETE DOMINANCE1. In flowers there is a gene for Red (R)

which has incomplete dominance to the recessive color white (r). The heterozygote plant produced by a white and red flower is pink

RR rr Rr

SOLVE THE FOLLOWING CROSSES: INCOMPLETE DOMINANCE

B= BLACK (INCOMPLETE DOMINANCE)B = YELLOW (RECESSIVE)

What is the genotype for a dog that is Black : ______

What is the genotype for a dog that is Yellow :_____

What is the genotype for a dog that is Brown: ______

Show a cross between a Brown dog and a yellow dog.

BB

bb

Bb


B

b

b

b Bb bb

Bb bb


WHAT PERCENTAGE OF THE PUPPIES ARE

BB=_________Bb=__________bb= __________

0%50%50%

B = BLACK FUR (INCOMPLETE DOMINANCE)B= WHITE FUR (RECESSIVE)What do you think the genotype would

be for the mother sheep if she has white fur: ____________

What do you think the genotype would be for the father sheep if he has black fur:_______________

What color would a Bb sheep be: __________________________

bb

BB

Gray


B

b

B

b Bb Bb

Bb Bb


WHAT PERCENTAGES WILL THE F1 BE:

BB: _______% Bb: ________% bb: ________% Black:_________% White:_________% Hybrid: ________%

01000

00100

Solving Genetics Problems

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