Genetics Worksheet

Genetics Worksheet

Inheritance lab                            Name: ________________________


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  • What are the possible offspring genotypes of a male that is heterozygous for eye color and a female that is homozygous recessive for eye color? If brown is dominant over blue, what are the parents’ phenotypes? (2pts)








  • If two heterozygous individuals mate and have one offspring, what is the probability the offspring would have the recessive trait? (2pts)









  • If a rat that is homozygous dominant for a trait mates with a rat that is homozygous recessive for the same trait, what is the probability that the two will produce a homozygous recessive offspring? (2pts)










  • What are the possible genotypes of the parents for an individual that is homozygous dominant for a trait? (2pts)








  • Two parents of the same phenotype have an offspring who has a different phenotype. If the trait is controlled by one gene, what are the genotypes of the parents and offspring? (2pts)








  • FAMILY TREES (15pts)


Determine the genotype of the 15 people in this family for the gene for attached (dark) versus unattached (white) earlobes. Circles are males; squares are females. The two parents are connected with a line Children are below couples, connected by a line perpendicular to the line connecting the parents. (for example: 1&2 are parents of 5,6&7).



To accomplish this: 1) find a couple who have the same phenotype but have an offspring that is different than they are (like in the question before this one). This will help you figure out who is recessive (which can only be homozygous recessive). The all the ones with the same color will be recessive. 2) The other phenotype is dominant.  Try to figure out who is homozygous dominant and who is heterozygous by looking at the offspring or the parents of the individual. 3) if it is impossible to know if they are, write  “AA/Aa” if you are using the letter “a” for the gene, for instance. Write the genotype above and close to each individual.




















Same family. Different gene. Use a different letter.




  • Probabilities: 5points


If I have one child, the chance of a boy is 1/2: B or G


If I have two chidren, the chances of two boys is 1/4 : BB, BG, GB or GG


Write out the 8 possibilities for the order of children if I have three children:






What is the probability of having three girls?



Circle the ones above that have two boys and a girl.

What is the probability of having two boys and a girl?



  • Blood type: (5pts)

There are four blood types: A, B, AB and O

We will use the letter I for the gene: I or i for the dominant and recessive allele respectively.

This is a strange gene that has three alleles, two of which are co-dominant, meaning they are expressed when they are present.  We give them different superscripts: IA and IB.


Type A blood can be either IA IA or IA i

Type B blood can be either IB IB or IB i

Type AB blood is IA and IB. Remember BOTH are dominant, so both are expressed.

Type O blood is homozygous recessive: ii



Draw a punnett square to determine the offspring of a parent with type AB blood  and a parent with type O blood.










Demonstrate how a parent with Type A blood and a parent with type B blood could have a child with type O blood.