Name ___________________________________________ date _______________ per _____________
Monster Genetics
You must complete the following pre learning in order to prepare to build your monster.
Monster Genetics Pre Learning: Read the following information, complete the Punnett squares, and
answer the questions. Pre lab MUST be completed BEFORE beginning the Monster Genetic Lab.
Important vocabulary:
Phenotype
Genotype
Dominant
Recessive
Allele
Gene
Trait
P generation
F1 generation
F2 generation
Chromosome
Punnett square
Homologous Chromosome
Mendelian Inheritance – Simple Dominant, Simple Recessive, & the Rule of Dominance
Simple dominance is an inheritance pattern where the dominant allele (noted as a capital letter) always
trumps the recessive allele when present. For example: T = the dominant allele for tall plant and t = the
recessive allele for a short plant.
1. Plants with the genotypes TT or Tt will be ________________.
2. How many dominant alleles are needed for the dominant phenotype to be expressed (seen). ___
The only time the recessive phenotype is expressed is in the homozygous recessive genotype.
3. Plants with the genotype tt will be _________________.
In humans, polydactyly (having extra fingers or toes) follows a simple dominance inheritance pattern.
Polydactyly is actually the dominant trait, but there is a low frequency of the dominant allele in the
population. Create a Punnett square for a man who is heterozygous for Polydactyly and a woman who has
normal numbers of fingers and toes.
P = Polydactly
P = normal number
of fingers & toes
Simple Dominance, used when referring to the dominant trait, and Simple Recessive, used when referring to
the recessive trait, are both considered Mendelian Inheritance because they follow the Rule of Dominance
described by Mendel.
Incomplete Dominance Inheritance
Incomplete Dominance occurs when the heterozygote phenotype is a blending of the dominant and recessive
phenotypes. Neither the dominant nor the recessive phenotypes are expressed (shown) but rather an
intermediate or blended phenotype is expressed in the heterozygous. Incomplete Dominance Inheritance has
a special genotype notation that uses a capital letter for the dominant allele and the same capital letter with
an accent mark (‘) for the recessive allele.
For example: a homozygous dominant plant TT = Tall
homozygous recessive plant T’T’ = short
4. In Incomplete Dominance Inheritance the heterozygous plant TT’ would be ________height.
The color of a particular species of mouse is inherited through Incomplete Dominance Inheritance. A
homozygous dominant Black mouse is crossed with a homozygous recessive white mouse.
5. What is the genotype of the Black mouse? ______________
6. What is the genotype of the White mouse? ______________ (remember the special notation for
Incomplete Dominant Inheritance)
7. Complete the Punnett square for a cross between
the Black mouse and the White mouse.
8. What color will the F1 generation be? _____________
9. What is the genotype of the F1 generation? ________
In humans, the trait for sickle cell anemia is incompletely dominant. A person who is heterozygous for the
sickle cell trait has less severe anemic symptoms than the homozygous recessive person. Sickle cell
heterozygotes are also resistant to malaria.
Co-dominant Inheritance
Co-dominant Inheritance is when both alleles are dominant, neither one is recessive to the other. The
heterozygote expresses (shows) both phenotypes equally. In the case of Co-dominant Inheritance each allele
is noted using a different capital letter. For example: Red=RR Black=BB Red with black stripes=RB
A chicken with all black feathers BB mated with a chicken with all white
feathers WW the offspring are referred to as checkered chickens
because they have both black feathers and white feathers. (see picture
on right)
10. Complete a Punnett square showing a cross between two
checkered chickens (chickens with both black and white) in the
F1 generation in the picture to the right.
11. What is the probability (% chance) of producing:
White chickens in the F2 generations? ________
Black chickens in the F2 generation? ________
Checkered chickens in the F2 generation? ________
In humans blood type is inherited co-dominantly. A mother with type A blood has blood cells with the A
protein on them. A father with type B blood has blood cells with the B protein on them. Their child with AB
type blood has blood cells that have both the A and the B protein on them.
Sex-linked Inheritance
Sex-linked Inheritance refers to the genes that are carried on the sex chromosomes. Females are XX and males
are XY. In females the sex chromosomes are homologous chromosomes, composed of the same genes in the
same order. In males the sex chromosomes are NOT homologues chromosomes, the X and Y chromosomes
are NOT homologous chromosomes; the genes found on the Y chromosomes are different from the genes
found on the X chromosome. The X chromosome is much larger than the Y chromosome, and contains more
genes than the Y, for this reason, most sex-linked traits are due to genes found on the X chromosome.
The notation for Sex-linked Inheritance includes the sex chromosome, for example:
XR = normal red/green vision which is dominant Xr = red/green color blindness which is recessive
12. If “which is dominant” and “which is recessive” was NOT written above, how would you have known
that red/green color blindness is recessive?
13. A girl with the genotype XR Xr has what type of vision? _______________________________
14. A boy with the genotype XR Y has what type of vision? ________________________________
15. If the boy above had inherited the recessive allele from his mother his genotype would be _____
a. His phenotype would be? ________________________________
Explanation: Girls who inherit the gene for red/green colorblindness from their mothers Xr still have a chance
to inherit the dominant, normal gene from their father XR . A girl who is heterozygous for a recessive Sexlinked trait is said to be a carrier. Boys who inherit the gene for colorblindness Xr from their mothers don’t get
that second chance because the Y chromosome they inherit from their fathers does not contain any gene for
color vision, normal or not. After reading the explanation, go back and check your answers for numbers 12 –
15a, make corrections if you need too.
16. Why are more sex linked recessive traits seen in males?
Complete the following for practice:
Snap dragons (flowers) are incompletely dominant for color; they have phenotypes red, pink, or
white. The red flowers are homozygous dominant, the white flowers are homozygous recessive, and
the pink flowers are heterozygous. Give the genotypes for each of the phenotypes using R and R’
Red snapdragon genotype _________ pink snapdragon _________ white snap dragon _________
Show genetic cross between a pink snap dragon and a red snap dragon.
__________ x __________
Will any white snapdragons be produced? _________
How do you know your answer is correct?
In Smileys, eye shape can be Starred = SS, Circular = CC, or a Circle with a Star = CS
What type of inheritance is demonstrated in the eye shape of these smileys? ___________________________
Write the genotypes for the pictured phenotypes below.
Genotypes:
________
_________
_________
Show the cross between a star-eyed and a circle eyed _________ x _________.
What are the phenotypes of the offspring? _____________________
What are the genotypes? ____________________
Show a cross between a circle star eye and a star eye ________ x _________
How many of the offspring are circle eyed? _________
How many of the offspring are circle-star eyed? _____________
Sex-linked Inheritance In fruit flies, eye color is a sex linked trait. Red is dominant to white.
1. What are the sexes and eye colors of flies with the following genotypes:
X R X r _________________
X R Y _________________
X R X R _________________
X r Y _________________
2. What are the genotypes of these flies:
white eyed, male ____________
red eyed female (heterozygous) ________
white eyed, female ___________
red eyed, male ___________
3. Show the cross of a white eyed female X r X r with a red-eyed male X R Y .