What's the Father? - Extra Credit

Mr. Bartlett recently posted pictures of a litter of puppies from his dog. Shortly after, Mr. Quick forwarded us the email asking to determine the genotype of the father based off the phenotypes of the mom and puppies. (very, very cute mom and puppies)

This problem is very similar to one we did on a quiz regarding genetics and a powerpoint lecture in class. I will use this reference below as a source to solve this question.

The first given I receive is the number of puppies in the litter: 12. After this, I determine the colors and ratios of the mother and offspring from the picture. From the first picture, I determine the mother is a yellow dog with a pale nose and lips. According to this chart, that means her genotype can only be "bbee".

Next I look at the ratio of puppies and the color variation. Out of the 12 puppies, I see that 5 are brown, so the other 7 must be black. So now there is a ratio of:

5/12 - Brown (bbEE or bbEe)

7/12 - Black (BbEE or BbEe) 

The recessive gene, b, for black and brown would make sense considering the mother's genotype, bbee. 

Now it is time to begin hypothesizing the possible genotype for the father. The first important factor is noticing there must be a dominant gene B in the father since black (Bb) puppies were produced. However, it is clear he is not homozygous dominant for the B gene because of the brown/chocolate puppies. If he had been BB, all of the puppies in the litter would come out black because of the mother's recessive genes for yellow. So the mother's bb, along with the father's Bb, would make sense for a Bb - black, and a bb - brown mix in the litter.

Next is the E allele. The mother's genotype for the allele is homozygous recessive (ee). For both black and brown puppies, either a homozygous dominant (EE) or heterozygous (Ee) is present in both genotypes. However, I can eliminate the heterozygous option based on the litter. Because only black and brown puppies were produced, it is safe to say that the father had an EE genotype. If you consider the mother, ee, mixing with the father, EE, they would only produce Ee in their offspring. If the father was heterozygous (Ee) for this allele, there would be a possibility of a yellow puppy in their mix. So from this information, I can confidently determine the father's genotype for this trait is EE.

From solving both parts of the traits, I concluded the father's genotype as BbEE - a black lab. 

If I put this into a punnett square: 

We see that 50% of the puppies will be black, and that 50% of the puppies will be brown. This is almost identical to the 5/12 and 7/12 ratio which was experienced in the litter. 

I'm sure the two make a very cute couple!