Download Dominant Trait - Georgetown ISD

Know these terms:
Alleles – forms of a trait – you have 2 for every trait…one from your mom and one from
your dad. They are represented with a letter (P for purple, p for white, for example)
Homozygous – having alleles that are the same for a trait (PP or pp, for example)
Heterozygous – having alleles that are different for a trait (Pp)
Dominant – the trait that shows up, if present
Recessive – the trait that only shows up if present in the homozygous form
Phenotype – how an individual looks, the physical result of the genotype
Genotype – the alleles that are inherited.
From there genetics is mostly working punnett squares and predicting outcomes of
crosses.
Here are a few examples. I am not comfortable posting the answers online. Come see
me for a key and/or if you need any help with these:
Introduction to Punnett Squares: Practice
Trait
Pod shape
Pod Color
Flower Position
Plant Height
Dominant Allele
Smooth (N)
Green (G)
Axial (A)
Tall (T)
1. Nn X NN
Recessive Allele
Constricted (n)
Yellow (g)
Terminal (a)
Short (t)
Genotype:
Phenotype:
2. Aa X aa
Genotype:
Phenotype:
3. Tt X Tt
Genotype:
Phenotype:
4. Cross two plants that are heterozygous for green pods
Genotype:
Phenotype:
5. Cross a plant that is heterozyogous for axial flowers with a plant that has terminal
flowers.
Genotype:
Phenotype:
6. Cross a homozyogous tall plant with a short plant
Genotype:
Phenotype:
7. Cross a plant that is heterozygous for smooth pods with a plant that has constricted
pods,
Genotype:
Phenotype:
8. When a tall plant is crossed with a short plant, some of the offspring are short. What
are the genotypes of the parents and the offspring? What is the phenotypic ration in the
offspring
Parent genotypes:
Offspring genotypes:
Phenotypic ratio:
9. Three fourths (3/4) of the plants produced by a cross between two unknown pea
plants have axial flowers and the other ¼ have terminal flowers. What are the genotypes
of the parent plants?
Parent Genotypes
10 What cross would result in ½ of the offspring having green pods and ½ of the offspring
having yellow pods?
Cross:
11. List the cross or crosses that you could use in order to guarantee that the offspring
would have axial flowers:
12. List the cross or crosses that you could use in order to guarantee that at least some of
the offspring would have terminal flowers.
13. Cross a plant that is homozygous dominant for pod color with a plant that is
homozygous recessive for pod color.
Genotype:
Phenotype:
14. Take the offspring from the cross in #13. Self pollinate those offspring. Predict
what the next generation will look like
Genotype:
Phenotype:
A little harder,,,
1..A cross between 2 heterozygous plants yields 1252 offspring. How many are
dominant and how many are recessive?
2. A cross between a homozygous recessive parent and a heterozygous parent yields 350
dominant offspring. How many recessive would you expect? What is the total number
of offspring?
3. Two unknown parents cross and produce 36 offspring. 9 of them are homozygous
dominant, 18 of them are heterozygous dominant, 9 of them are homozygous recessive.
What is the genotype of the parents?
4. If a pea plant that is heterozygous for 2 traits (Tall and purple) is crossed with a plant
that is homozygous recessive (short and white), what portion of the 9822 peas that are
produced would yield plants that are tall and white?
5. If a pea plant that is heterozygous for 2 traits (Tall and purple) is self pollinated,
what portion of the 9822 offspring would be tall and white?
Dihybrid, sex linked, incomplete dominance, multiple
alleles
Dominant Trait
Black Fur
Brown eyes
Axial flowers
Green peas
Five fingers per hand
Attached earlobes
Blood Clotting factors
Color vision
Short hair
Recessive Trait
Brown fur
Blue eyes
Terminal flowers
Yellow Peas
Six Fingers per hand
Unattached earlobes
No blood clotting factors (hemophila)
Color blind
Long hair
1. A homozygous short-hair, homozygous brown fur rabbit is crossed with a heterozygous
short-hair, heterozygous black fur rabbit.
Cross ___________________
Genotype________________
Phenotype _______________
2. If the offspring of a person with attached earlobes and a person with unattached earlobes has
any chance of having unattached earlobes what must the genotype of the parents be? What is
the offsprings’ chance of having unattached earlobes?
Cross ______________
Phenotype ______________
3. Cross a homozygous black dog with a homozygous white dog if you assume incomplete
dominance.
Cross _________________
Phenotype _____________
Genotype ______________
4. A homozygous 5-fingered man meets and marries a 6-fingered woman. What are the chances
that their children will have 6 fingers? (Not a sex linked trait!!)
Cross _______________
Genotype ____________
Phenotype _____________
Chance _______________
5. Looking back at #4, suppose one of the male children of the couple met and married a
woman who has 6 fingers. What will those children look like?
Cross ________________
Phenotype ____________
Genotype _____________
6. A woman who is heterozygous for the color blind gene meets and marries a man who has is
not color blind. Remember that color blindness is a sex linked trait.
Cross __________________
Genotype _______________
Phenotype _______________
7. A woman who is color blind meets and marries a man who is not color blind. Remember that
color blindness is a sex linked trait.
Cross __________________
Genotype ______________
Phenotype _______________
8. A woman who is heterozygous for hemophilia meets and marries a man who has hemophilia.
Remember that hemophilia is a sex-linked trait
Cross __________________
Phenotype ______________
Genotype _______________
9. A yellow pea, homozygous axial flower pea plant crosses with a heterozygous green,
terminal pea plant.
Cross __________________
Phenotype ______________
10. A homozygous black fur rat crosses with a homozygous brown fur rat.
Cross __________________
Phenotype ______________
Genotype _______________
11. Any of the offspring in #10 cross with each other.
Cross __________________
Genotype ______________
Phenotype _______________
12. A yellow flower crosses with a blue flower. Incomplete dominance occurs in these flowers
(Hint: Ziplock commercial “Yellow and blue make green.”)
Cross __________________
Genotype _______________
Phenotype ______________
13. Red and white flowers with incomplete dominance cross.
Cross __________________
Genotype _______________
Phenotype ______________
14. The offspring of the cross in #13 are crossed again
Cross __________________
Genotype _______________
Phenotype ______________
15. If someone with type O blood marries someone with type AB what are the genotypes and
phenotypes of the possible offspring?
16. If someone who is homozygous for type A blood marries someone who is heterozygous for
type B, what are the genotypes and phenotypes of the possible offspring?
17. A child has type O blood. Which one blood type could neither parent be?
What are the possible genotypes of his parents (list all).
18. If a child has type A blood and his mother is homozygous for type A blood, does his dad
have to also have type A blood? _______ What blood types could his dad be?
19. You are on the jury during a trial and the prosecutor tells you and the other jury members that
they have found type A blood in the accused man’s car. He has type B blood and the victim has
type A blood. He says that establishes that the victim’s body was in the accused man’s car. Is
that right? Why or why not?
What if instead of blood type, they have DNA that matches the victim?