Genetics: Unit 3 Assignment
Genetics includes the study of our genetic makeup and how that influences physical traits or disease states. Our genetic makeup can be defined by the contributions from both parents. Your workplace is trying to solve an issue and because of your genetic expertise they have asked you to prepare answers to the following scenarios.
Question 1
A woman recently found out she is pregnant and her doctor informed her that they will be performing a blood test to determine if she is a carrier of the Cystic Fibrosis (CF) trait.
- Is Cystic Fibrosis inherited in an autosomal dominant or recessive manner? Explain.
Answer. Cystic Fibrosis is inherited via autosomal recessive inheritance where the gene is located on one of the autosomes. Males and females are equally affected by this type of inheritance. Due to the “recessive” characteristic, two copies of the genes –one from each parent- must be present in order for the trait to be passed on to the offspring. A person with one copy of the gene is called a carrier and do not usually show any signs of the disease.
- The blood test confirmed the woman is a carrier of the Cystic Fibrosis trait. What is her genotype?
Answer. Her Genotype is CFTR which stands for Cystic Fibrosis Transmembrane Conductive Regulator gene. This implies that her chromosomes have a deletion of the codon for phenylalanine in the amino acid polypeptide.
A Punnett square applies the rules of probability to predict the possible genotypes and phenotypes of offspring. Complete the following Punnett squares demonstrating the potential offspring and risk for inheriting Cystic Fibrosis. You can choose the letter to denote the trait.
- The mother is a carrier of the Cystic Fibrosis trait and the father does NOT have the Cystic Fibrosis trait.
______Ff_____ x _____FF_____
| F | f | |
F | FF | Ff |
F | FF | Ff |
Genotypic ratios: ________2:2__or______50%Ff 50% FF__________
Phenotypic ratios: ___________4:0___or 0% cystic fibrosis trait____________
- The mother is a carrier of the Cystic Fibrosis trait and the father is also a carrier of the
Cystic Fibrosis trait.
_______Ff____ x _____Ff_____
| F | f | |
F | FF | Ff |
f | Ff | ff |
Genotypic ratios: __________1:2:1____or___25% FF 50% Ff 25% ff_________
Phenotypic ratios: ____________3:1____5% of the offsprings will have cystic fibrosis. 50% will be carriers and 25% will be unaffected__________
Question 2
Red-green colorblindness is a recessive mutation that is found on the X chromosome and therefore termed an X-linked inheritance pattern. Remember to use the X and Y symbols to denote the sex and capitol and lowercase letters to represent the color-blind traits.
- A colorblind female has children with a normal male. What are the parental genotypes?
______Xx_____ x _____XY_____
| Xb | Xb | |
XB | XBXb | XBXb |
Y | YXb | YXb |
Genotypic ratios: ___________2:2 or 50% XBXb: 50% YXb_______________
Phenotypic ratios: ___________50% will inherit the phenotype, specifically the sons_______________
- Explain why X-linked recessive traits are more common in males. Who does a son inherit the trait from?
Answer. X-linked recessive traits are more common in males because males are hemizygous with only one X chromosome and one Y chromosome. The Y chromosome does not carry alleles. This leads to the phenotype being expressed in every male who receives the trait from a female carrier. On the other hand, females have two X chromosomes, meaning that a female who has one copy of the mutation does not express the phenotype.
Question 3
For this question, you can assume that the following traits are controlled by single locus genes and are located on different chromosomes. Phenylthiocarbamide (PTC) is a dominant trait that you can attribute the ability to taste bitterness by a receptor on the tongue. The ability to taste bitterness is dominant over being tasteless. Freckles are controlled primarily by the MC1R gene. Freckles show a dominant inheritance pattern. Suppose a freckled woman who can taste bitterness has a father who is does not have freckles and cannot taste PTC. She then has children with a heterozygous, freckled man who can also taste bitterness.
a) Please provide the genotypes of the parents on the line above the Punnett Square.
b) Complete the dihybrid cross.
c) List both the genotypes and phenotypes of their offspring.
___________________________x ___________________________
| FB | Fb | Fb | fb | |
| FB | FFBB | FBFb | FBFb | FBfb |
| Fb | FbFB | FbFb | FbFb | Fbfb |
| Fb | FbFB | FbFb | FbFb | Fbfb |
| FB | FBFB | FBFb | FBFb | FBfb |
Genotypes:
2/16 have PTC
12/16 have freckles
2/16 have both PTC and freckles
Phenotypes:
12:2:2 is the ratio for inheriting freckles
Question 4
The pedigree below traces the inheritance of alkaptonuria, a biochemical disorder. Affected individuals, indicated here by the filled-in circles and squares, are unable to break down a substance called alkapton, which colors the urine and stains body tissues.
- Does alkaptonuria appear to be caused by a dominant or recessive allele? Explain.
Answer. Alkaptonuria appears to be caused by a recessive gene. If the condition is caused by a dominant allele, Carla should not express the phenotype. All infected individuals, including Arlene, Wilma, tom, and Carla are homozygous recessive while George is Aa since some of his children express the phenotype. Accordingly, Daniel, Ann, Alan, and Sm are Aa since each has one affected parent. Since Ann is heterozygous, Michaal is Aa because both have an affected child.
- What is George’s phenotype?
Answer. George is heterozygous. He is a carrier.
- Is it possible for Daniel to have a child with alkaptonuria? Explain.
Answer. It is possible for Daniel to have a child with alkaptonuria but only when he marries either a heterozygous or homozygous woman.
- Does the first child’s genotype have an influence on the probability of the second child having PKU? Explain.
Answer. Yes, if the first child gets the disorder, this increases the probability of the future child inheriting the condition.
- How would knowing the pattern of inheritance influence the treatment plan for this disease?
Knowing the pattern helps doctors make adequate preparations for treatment.
Question 5
Two mothers give birth to sons at the same time at a busy hospital. The son of mother 1 has hemophilia, neither parent has the disorder. The son of mother 2 does not have hemophilia, but his father does. Several years later, couple 1 sues the hospital claiming the boys were switched at birth. Did the hospital switch the babies? Explain and use the Punnett Square to defend your answer.
a) Possible Punnett Squares to represent the potential crosses that occurred having either son.
Son from Mother 1: _____Xx______ x ____XY______
| X | x | |
X | XX | Xx |
Y | XY | xY |
Son from Mother 2: _____XX______ x ____xY______
| X | X | |
x | Xx | Xx |
Y | XY | XY |
b) Explanation:
The sons were not switched at birth. It is important to note that while mother 1 may not have had hemophilia, she may have been a carrier of the disorder. This implies that there was a likelihood of her passing the trait to the son as shown in the first Punnett Square. On the other hand, mother 2 was not a carrier and even if the father did have the disease, there was no likelihood of the son inheriting the trait from him.
