Biology Homework

Biology Homework

  1. Describe both the primary gene or protein defect and the resulting phenotype for the following diseases
    a: Cystic fibrosis, b. Marfan syndrome

Cystic Fibrosis is a condition that affects the pancreas, liver, intestines, and lungs, making the organs develop a thick muscular layer. The protein mutated by cystic fibrosis is regarded as CFTR (cystic fibrosistransmembraneconductance regulator). Those with Marfan syndrome often have long limbs and thin-fingered legs. This results from a disorder in the connective tissue. The Marfansyndrome is caused by a gene known as FBN1that is situated on the 15q21.1. Chromosome, q arm, region 2 bands 1, sub-band 1.

  1. The father of 12 children begins to show symptoms of Huntington disease. What is the probability that Sam the man’s second oldest son (II-2), will suffer from the disease if he lives a normal life span? (Sam’s mother and her ancestors do not have the disease.)

Huntington’s disease is considered as a dominant genetic disorder. For an allele Hthat represents the disorder and h that represents no disorder, those with Hhwill acquire the Huntington’s disease. The S’s father has Huntington’s disease. This means that his genotype can HHor Hh. S’s mother lacks the disease or a family history of the condition, meaning that her genotype is hh.

If the genotype of Sam’s father is HH, Sam will get only the genotype Hhwhere H comes from father and h from the mother. This means that Sam will have the disease. But if Sam’s father is heterozygous Hh, a Punnetsquare can be used for crossing between Hh and hh.

  H h
h Hh hh

From this, it can be deduced that there is a 50% probability that Sam will develop the hhgenotype and 50% probability that Sam will develop genotype Hh.

  1. Define penetrance and expressivity.

Penetrance is the probability of a trait or genebeing expressed. Expressivity is the variation in phenotypic expression in cases where an allele is a penetrant.

  1. In the following pedigree, assume that the father of the proband is homozygous for a rare trait. What pattern of inheritance is consistent with this pedigree? In particular, explain the phenotype of the proband. (Consider a rare trait here to be less than 1 in 30,000.)

From this pedigree, it can be deduced that there is an autosomal recessive trait because only two of the three children indicates inheritance of the trait. A homozygous dominant would have passedthe trait to all the children.

  1. A young boy is color blind. His one brother and five sisters are not. The boy has three maternal uncles and four maternal aunts. None of his uncles’ children or grandchildren is colorblind. One of the maternal aunts married a colorblind man, and half of her children, both male, and female are colorblind. The other aunts’ married man who has normal color vision. All their daughters have normal vision, but half of their sons are color blind.
  2. a) Which of the boy’s four grandparents transmitted the gene for colorblindness?

Maternal grandfather

  1. b) Are any of the boy’s aunts or uncles color blind?


  1. c) Is either of the boy’s parents colorblind?


  1. How is mitochondrial DNA transmitted to children?

Mitochondrial DNA is a genetic material present in the mitochondria. It is passed down from mothers to their children. However, sons are not capable of passing down their mothers’mtDNAto their children because an mtDNA is passed through a female egg.

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