GENETICS PROBLEMS - Part 1
BIOL 1406
 
 

MONOHYBRID CROSS PROBLEMS:

 Characteristic of Mendel's Peas

Dominant allele

Recessive allele

        Flower Color            Purple (F)               white (f)
        Seed Color            Yellow (G)               green (g)
        Seed Shape            Round (R)               wrinkled (r)
        Stem Length            Tall (T)               dwarf (t)
 
1. A plant that is homozygous for yellow seeds is crossed with a plant that is homozygous for green seeds.  What percentage of the F1 generation would you expect to have yellow seeds?

 

 

 

GG  X  gg

 

 

 

  T t
t Tt tt
t Tt tt

 

 

 

100% Yellow Seeds in F1

 

2. A plant that is heterozygous for tall stem length is crossed with a plant that has dwarf stem length.  What percentage of the F1 generation would you expect to have dwarf stem length?

 

 

 

Parent Genotypes:     Tt  X  tt

Gametes Formed:  T,t             t,t

 

 

 

  T t
t Tt tt
t Tt tt

 

 

 

50% Dwarf Stems in F1

 

3. A plant that has wrinkled seeds is crossed with a plant that is heterozygous for round seeds.  What percentage of the F1 generation would you expect to have round seeds?

 

 

 

Parent Genotypes:        rr   X   Rr

Gametes Formed:     r,r               R,r

 

 

 

  r r
R Rr Rr
r rr rr

 

 

 

50% Round Seeds in F1

 

 

4. A plant that is heterozygous for purple flowers is self-pollinated (crossed with itself).  What would be the expected phenotype ratio of the F1 generation?

 

 

 

Parent Genotypes:          Ff   X   Ff

Gametes Formed:        Ff               Ff

 

 

 

  F f
F FF Ff

f

Ff

ff

 

 

 

F1 Phenotype Ratio:

 

 

 

3 Purple : 1 White

 

5. A plant that is homozygous for tall stem length is crossed with a plant that is homozygous for dwarf stem length.  What would be the phenotype of all the offspring in the F1 generation?

 

 

 

Parent Genotypes:   TT   X   tt

Gametes Formed:  TT             tt

 

 

 

  T t
T TT Tt
t Tt tt

 

 

 

F2 Phenotype Ratio:

 

 

 

3 Tall : 1 Dwarf

 

6. A gardener has a plant that produces yellow seeds.  If he does a test cross, what would be the genotype of the plant he would use for the test?

 

 

 

Genotype of plant for test cross: gg (green seeds)

 

 
If the test cross produces offspring that are 48% yellow and 52% green, what is the genotype of the original plant?

 

 

 

Genotype of plant with yellow seeds: Gg

 

 

DIHYBRID PROBLEMS:

 
7. A plant that is homozygous for green seeds and heterozygous for tall stem length is crossed with a plant that is heterozygous  for yellow seeds and homozygous for tall stem length.  What is the expected phenotype ratio of the F1 generation.

 

 

ggTt   X   GgTT

 

Gametes: gT, gt, gT, gt                                     GT, GT, gT, gT 

 

 

 

  gT gt gT gt
GT GgTT GgTt GgTT GgTt
GT GgTT GgTt GgTT GgTt
gT ggTT ggTt ggTT ggTt
gT ggTt ggTt ggTT ggTt

 

 

 

Yellow & Tall   = 50%

Yellow & Dwarf  = 0

Green & Tall    = 50%

Green & Dwarf   = 0

 

 

8. A plant that is homozygous for purple flowers and homozygous for dwarf stem length is crossed with a plant that is homozygous for white flowers and homozygous for tall stem length.  What are the genotypes of all the F1 generation -- WITHOUT WORKING THE PUNNETT SQUARE!

 

 

Parental Genotypes:  FFtt  X  ffTT

F1 Genotype: FfTt

 

HUMAN TRAIT Dominant Allele Recessive Allele
Dimples D - have dimples d - no dimples
Earlobes E - free/unattached e - attached
Eye Color B - pigmented iris/brown b - non-pigmented/blue
Freckles F - freckles present f - no freckles
Little Finger L - bent little finger l -  straight little finger
Tongue-Rolling R - can roll tongue r - can't roll tongue
 
9. Two parents have the following genotypes: Dad - BbEe and Mom - bbee.  What are the phenotypes of the two parents?

 

 

 

Parental Genotypes:   BbEe   X   bbee

 

Parental Phenotypes: Brown eyes, Free earlobes

                     Blue eyes, Attached earlobes

 

Gametes Formed: BE, Be, bE, be      be, be, be, be

 

 

 

 be
BE BbEe
Be Bbee
bE bbEe
be bbee

 

 

What chance is there that a child of theirs would have blue eyes and attached earlobes?

 

1/4 or 25% chance of child with blue eyes and attached earlobes 

 

10. Dad is heterozygous for freckles and homozygous for no dimples.  Mom is homozygous for no freckles and heterozygous for dimples.  What is the genotype of each parent?  What is the percentage chance that a child of theirs would have both freckles and dimples?

 

 

 

Parental Genotypes:    Dad            Mom

                                          Ffdd     x     ffDd

 

 

Gametes Formed: Fd, Fd, fd, fd      fD, fd, fD, fd

 

 

 

  Fd fd
fD FfDd ffDd
fd Ffdd ffdd

 

 

 

1/4 or 25% chance of child with freckles and dimples

 

11. One parent is homozygous for a straight little finger and heterozygous for free earlobes and the other parent is heterozygous for both a bent little finger and free earlobes.  What is the percentage chance that they will have a child who has a bent finger and attached earlobes?

 

Parental Genotypes:       llEe      X        LlEe

Gametes Formed:  lE, le, lE, le         LE, Le, lE, le

 

  lE le
LE LlEE LlEe
Le LlEe Llee
lE llEE llEe
le llEe llee

 

1/8 or 12.5% chance of child with bent little finger and attached earlobes

 

12. A man is able to roll his tongue and has blue eyes?  His wife is not able to roll her tongue and has brown eyes.  If they have a child that cannot roll his tongue and has blue eyes, what is the genotype of both parents?

 

 

 

Parental Genotypes: Male    Female     Child

                    R_bb    rrB_       rrbb

 

 

Parents: Dad = Rrbb

         Mom = rrBb

     

 

DIHYBRID CROSSES w/ GUINEA PIGS:

 
GUINEA PIG TRAIT Dominant Allele Recessive Allele
Fur Texture R - Rough r - smooth
Fur Color B - Black b - white
 
13. A male guinea pig is heterozygous for rough fur and homozygous for black color.  The female guinea pig is homozygous for smooth fur and heterozygous for black color.  What is the genotype for each of the parents?

 

 

Parental Genotpes:          RrBB  X   rrBb

 

Gametes Formed:  RB, RB, rB, rB        rB, rb, rB, rb 

 

 

What are the four possible phenotype combinations in their offspring and the percent chance for each?

 

 

Rough & Black  = 2

Rough & White  = 0

Smooth & Black = 2

Smooth & White = 0

 

14. If you mate two guinea pigs who are both heterozygous for rough fur and black in color, what would be the phenotype ratio of their offspring?

 

 

Parental Genotypes:         RrBb    X    RrBb

Gametes Formed:   RB, Rb, rB, rb         RB, Rb, rB, rb

 

 

 

 RB Rb rB

rb

RB RRBB RRBb RrBB RrBb
Rb RRBb RRbb RrBb Rrbb
rB RrBB RrBb rrBB rrBb
rb RrBb Rrbb rrBb rrbb

 

 

Rough & Black  = 9

Rough & White  = 3

Smooth & Black = 3

Smooth & White = 1

 

15. If a guinea pig that is heterozygous for rough fur and white in color is mated with a guinea pig that is heterozygous for both rough fur and black color, what would be the expected genotype ratio in the F1 generation?

 

Parental Genotypes:         Rrbb  X    RrBb

Gametes Formed: Rb, Rb, rb, rb        RB, Rb, rB, rb

 

 

 Rb rb
RB RRBb RrBb
Rb RRbb Rrbb
rB RrBb rrBb
rb Rrbb rrbb

 

RRBb = 1

RrBb = 2

RRbb = 1

Rrbb = 2

rrBb = 1

rrbb = 1

 

16. A breeder has a guinea pig that is black with rough fur.  If this guinea pig is mated with a white, smooth guinea pig and the offspring produced are 4 black with rough fur and 3 white with rough fur, what is the genotype of the black, rough parent guinea pig?

 

Black, rough fur guinea pig = B_R_

 

White, smooth guinea pig = bbrr

 

Offspring:  4 Black with Rough Fur

            3 White with Rough Fur

 

Genotype of black, rough furred guinea pig = BbRR