Question

1. which is unique to sexual reproduction?

a. new genetic combinations
b. cell division
c. offspring production
d. dna replication

1. what rna base replaces thymine in mrna?

a. uracil
b. cytosine
c. adenine
d. guanine

1. what process repairs tissue by producing identical cells?

a. mitosis
b. meiosis
c. binary fission
d. sexual reproduction

1. advantages of genetic variation include:

a. better adaptation to environmental changes
b. less mutation
c. identical offspring
d. fewer diseases

1. how is protein synthesis regulated?

a. stop codons signal end
b. start codons signal end
c. dna stops mrna
d. proteins regulate synthesis

1. which mutation type causes early stop codon that truncates protein?

a. nonsense mutation
b. silent mutation
c. missense mutation
d. frameshift mutation

1. what is the effect of crossing over in meiosis?

a. creates genetic diversity
b. produces identical cells
c. decreases chromosome number
d. repairs dna

Explanation:

• For question 21: Sexual reproduction involves the combination of genetic material from two parents, creating new genetic combinations. Cell division, offspring production, and DNA replication can occur in asexual reproduction too.
• For question 22: In RNA, uracil replaces thymine. Cytosine, adenine, and guanine are also present in RNA but do not replace thymine.
• For question 23: Mitosis is the process that repairs tissue by producing identical cells. Meiosis is for sexual - reproduction and produces non - identical cells, binary fission is a form of asexual reproduction in prokaryotes, and sexual reproduction does not directly repair tissue by producing identical cells.
• For question 24: Genetic variation allows for better adaptation to environmental changes. It does not necessarily lead to less mutation, does not produce identical offspring (which is a feature of asexual reproduction), and while it can be related to disease resistance in some cases, the main advantage is adaptation.
• For question 25: Stop codons signal the end of protein synthesis. Start codons signal the start, DNA is transcribed into mRNA but does not directly stop it in the context of regulation of synthesis, and proteins are the products of synthesis, not the regulators of the overall process in the way described.
• For question 26: A nonsense mutation causes an early stop codon that truncates the protein. A silent mutation does not change the amino - acid sequence, a missense mutation changes one amino - acid, and a frameshift mutation shifts the reading frame of the codons.
• For question 27: Crossing over in meiosis creates genetic diversity by exchanging genetic material between homologous chromosomes. It does not produce identical cells (mitosis does that), does not decrease chromosome number (meiosis I does that in a different way), and does not repair DNA.

Answer:

1. A. New genetic combinations
2. A. Uracil
3. A. Mitosis
4. A. Better adaptation to environmental changes
5. A. Stop codons signal end
6. A. Nonsense mutation
7. A. Creates genetic diversity