Question

question 19
which of the following is a nucleotide found in dna?

deoxyribose + phosphate group + cytosine
ribose + phosphate group + uracil
ribose + phosphate group + thymine
deoxyribose + phosphate group + uracil

question 20
a child is born with cystic fibrosis, an inherited recessive disorder.
no one in the family (on either side) for several generations is known to carry or have the disorder. how can this be explained?

the child developed the disorder when he was born; it is a result of a birth defect.
the genetic disorder is recessive, and can be carried by heterozygous individuals without ever being realized or identified.
the genetic disorder formed from the mothers poor nutrition and prenatal care.
the child contracted the illness from another child when he was born.

Explanation:

Question 19

DNA nucleotides consist of deoxyribose (sugar), a phosphate group, and a nitrogen - containing base (adenine, thymine, cytosine, or guanine). RNA has ribose (sugar), a phosphate group, and bases (adenine, uracil, cytosine, or guanine).

• Option a: deoxyribose + phosphate group + cytosine is a DNA nucleotide.
• Option b: ribose is in RNA, and uracil is an RNA base.
• Option c: ribose is in RNA.
• Option d: uracil is an RNA base.

Cystic fibrosis is a recessive disorder. Recessive disorders can be carried in a heterozygous state (carriers have one normal and one mutant allele) without showing symptoms. So, even if no one in the family for several generations has shown the disorder, parents could be heterozygous carriers.

• Option a: It is an inherited disorder, not a birth defect.
• Option b: Recessive disorders can be carried by heterozygous individuals (carriers) without symptoms.
• Option c: It is a genetic disorder, not caused by poor nutrition.
• Option d: It is an inherited disorder, not contracted.

Answer:

a. deoxyribose + phosphate group + cytosine

Question 20