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Genetics Practice #1

By Sue O'Bannon
Last updated almost 3 years ago
28 Questions
Note from the author:
Answer the questions below. If you need some help, GO TO Punnett Square Google Slides Presentation.
Answer the questions below. If you need some help, GO TO Punnett Square Google Slides Presentation.

For each genotype below, indicate whether it is heterozygous or homozygous.

  • gg
  • HH
  • ff
  • Dd
  • AA
  • Bb
  • Ee
  • Pp
  • heterozygous
  • homozygous
For each of the genotypes below determine what phenotypes would be possible.
Purple flowers (P) are dominant to white (p), Brown eyes (B) are dominant to blue (b).
PP = __________ ; Pp = __________ ; pp = __________ ; BB = __________ ; Bb = __________ ; bb = __________
For each phenotype below, list the genotypes possible. (remember to use the letter of the dominant trait)

Straight hair is dominant to curly ;Tail spikes are dominant to plain tails.
To get straight hair the genotype must be __________; for curly hair genotype must be __________.
To have spikes on the tail genotype must be __________ ; no spikes will develop if the genotype is __________

Have you recognized the patterns?
In order for a dominant trait to show, the organism must have __________. In order for the recessive trait to show, the organism must have __________.
Complete the Punnett squares for each of the crosses.
Tall (T) plants are dominant to short (t).
Tt x tt. Show what you should write in each box if the Heterozygous individual is on the top two boxes.
__________
__________
__________
__________
_______
_______
_______
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What percentage of the offspring from the cross above are tall? __________
What percentage are short? __________
Purple-flowered (P) plants are dominant to white-flowered plants. (p).
Pp x Pp. Show what you should write in each box if you cross two heterozygous individuals.
__________
__________
__________
__________
_______
_______
_______
_______
What percentage of the offspring from the cross above have purple flowers? __________
What percentage have white? __________

Yellow peas are dominant to green peas.
A Pea plant homozygous for yellow peas is crossed with one that produces green peas.

How many of the offspring plants will be hybrids that are heterozygous?

In guinea pigs, the allele for short hair is dominant to long hair.
What genotype would a heterozygous short haired guinea pig have? _______
What genotype would a homozygous short haired guinea pig have? _______
What genotype would a long-haired guinea pig have? _______
Show the cross for two heterozygous short-haired guinea pigs.
What is the probability of the offspring having short hair? __________
What is the probability of the offspring having long hair? __________

Also in guinea pigs curly hair is dominant to straight.
Show the cross between two homozygous curly haired guinea pigs.
What would be the chances of getting a straight-haired offspring?

Crosses and Punnett squares can also be used to predict genotypes of the parents. Doing this intentionally to determine parental genotypes is called a "testcross".

If two plants with purple flowers have offspring that show white flowers, which of the following must be true?

A guinea pig with short hair is crossed with one that has long hair. Over a period of many years, a scientist keeps records of the offspring and finds that 44 of them have curly hair and 46 of them have straight hair. Based on this data, what are the genotypes of the parents?
short-haired __________ x long-haired __________
Show the Punnett square of this cross to explain your reasoning.
In another laboratory, a short haired guinea pig is crossed with a long haired one, and over the course of several years, not a single offspring has long hair. Show the cross that explains this situation.
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