Genetics Study Guide – Who Gets the Money?

IntroductionYou will be demonstrating your knowledge of the various inheritance patterns and genetic models to solve a mystery involving genetics. You will need to be able to complete and analyze Punnett squares using multiple types of inheritance patterns and trace genetic traits.

Complete Dominance Incomplete Dominance Codominance Multiple Alleles Karyotypes Pedigrees

BackgroundThis story appeared in the local paper recently:

Five men show up, each claiming to be the couples’ long lost son who had run away to become a sheep-herder. You are called in as a genetics expert to decide who is the rightful heir. This mystery will be solved in three parts.

InstructionsComplete Parts One, Two, Three, and Four to determine which of the five men gets the money. You will receive partial credit along the way for each correct part even if you do not correctly solve the mystery.

Mr. and Mrs. James Smith died in a tragic farm accident when the tractor they were riding in rolled over in a ditch. Authorities found one million dollars hidden in a feed bin in the chicken coop. The couple is known to have a son, from whom they are estranged. This man is the sole heir to the Jones fortune.

Part One: Complete DominanceFreckles (F) are dominant over no freckles (f) and a widow’s peak hairline (H) is dominant over a straight hairline (h).

Below are descriptions of the phenotypes of Mr. and Mrs. Smith, as well as the five men who came forward to claim the money.

Name Freckles Genetics Hairline GeneticsMr. Smith Homozygous freckles Heterozygous widow’s peakMrs. Smith Heterozygous freckles Heterozygous widow’s peakCharlie Homozygous freckles Straight hairlineRyan Heterozygous freckles Homozygous widow’s peakDustin Homozygous freckles Heterozygous widow’s peakEric Heterozygous freckles Heterozygous widow’s peakRoss No freckles Homozygous widow’s peak

1. In the space below, draw two Punnett squares showing the possible offspring of Mr. and Mrs. Smith: one for freckles and one for hairline. Use the letters for the two alleles given above.

2. Write each person’s genotype in the table below:

Name Freckles Genotype Hairline GenotypeMr. SmithMrs. SmithCharlieRyanDustinEricRoss

3. Which man can be eliminated by these traits? EXPLAIN your reasoning.

Part Two: Pedigree and Karyotype AnalysisThere are still many men that could biologically be Mr. and Mrs. Smith’s son. Lawyers have asked for a pedigree of the Smith’s extended family to trace the presence of a cleft chin (shaded) throughout a family. No cleft chin is dominant to having a cleft chin (recessive). The Smith’s pedigree is pictured on the left.

Mrs. Smith also had an amniocentesis done while she was pregnant with her son and obtained a karyotype of his chromosomes. The karyotype of their son is pictured below on the right.

Name Cleft Chin Genetics Chromosome Number

Mr. Smith Heterozygous no cleft chin

46, XY

Mrs. Smith Heterozygous no cleft chin

46, XX

Charlie Cleft chin 46, XYRyan Heterozygous no cleft

chin46, XY

Dustin Cleft chin 46, XYEric Cleft chin 46, XY

4. Based on the pedigree, karyotype, and information above, which man can be eliminated? EXPLAIN your reasoning.

Mrs. SmithMr. Smith

Part Three: Incomplete Dominance and CodominanceNow that ________________________ have been eliminated, lawyers order blood tests to try to prove their claims. The lawyers have also done some research and read that hair texture is inherited.

Type A and type B blood are codominant over type O. Rh+ blood is dominant over Rh- blood. Hair texture exhibits incomplete dominance. Homozygous dominants (HH) have

curly hair. Homozygous recessives (hh) have straight hair. Heterozygotes (Hh) have wavy hair.

Below are descriptions of the phenotypes of Mr. and Mrs. Smith, as well as the remaining men who came forward to claim the money.

Name ABO Blood Type Rh Factor Hair TextureMr. Smith Heterozygous type A

bloodRh- Wavy hair

Mrs. Smith Type AB blood Homozygous Rh+ Curly hairCharlie Heterozygous type A

bloodHeterozygous Rh+ Wavy hair

Dustin Heterozygous type B blood

Heterozygous Rh+ Curly hair

Eric Type O blood Rh- Straight hair 5. In the space below, draw three Punnett squares showing the possible offspring of Mr. and Mrs. Smith for: blood type, Rh factor, and hair texture.

6. Write each person’s genotype in the table below:

Name Blood Type Genotype

Rh Factor Genotype

Hair Texture Genotype

Mr. SmithMrs. SmithCharlieDustinEric

7. Which men can be eliminated now? JUSTIFY your answers for each man.

Part Four: Multiple AllelesWe’re down to just ________________________. The lawyer now orders that a blood test to be performed.

A and B alleles are dominant to the O allele A and B alleles are co-dominant

Below are the results of the blood type test:Name Blood Test Outcome

Mr. Smith Type A bloodMrs. Smith Type A bloodCharlie Type B bloodDustin Type O blood

8. In the space below, draw a Punnett square showing the possible offspring of Mr. and Mrs. Smith. (Note: one of the children must code for the genotype of at least one of the remaining men).

9. Write the genotypes of each person in the table below. When possible, use two letters to represent both of the alleles they must carry.

Name Blood GenotypeMr. Smith

Mrs. Smith

Charlie

Dustin

10. So, WHO GETS THE MONEY? JUSTIFY your answer.