AP Biology: Genetics and Heredity (High School)

What are the complementary base pairs in DNA?

Answer: Adenine pairs with thymine; guanine pairs with cytosine.

What is a frameshift mutation?

Answer: An insertion or deletion not in multiples of three that shifts the reading frame.

What is a point mutation, and what kinds exist?

Answer: A change in a single nucleotide: silent (no change), missense (different amino acid), or nonsense (premature stop).

What happens during translation?

Answer: Ribosomes read mRNA codons and tRNAs deliver matching amino acids to build a polypeptide.

What happens during transcription?

Answer: RNA polymerase reads the DNA template strand and builds a complementary mRNA.

What is the central dogma?

Answer: DNA is transcribed into RNA, which is translated into protein.

What do DNA polymerase, helicase, and ligase do in replication?

Answer: Helicase unwinds the double helix; DNA polymerase adds nucleotides to the 3' end; ligase joins Okazaki fragments.

Describe semiconservative replication.

Answer: Each new DNA molecule has one original (parental) strand and one newly synthesized strand.

What does CRISPR-Cas9 do?

Answer: Uses a guide RNA to direct the Cas9 enzyme to cut DNA at a specific sequence, enabling gene editing.

What are restriction enzymes?

Answer: Enzymes that cut DNA at specific recognition sequences, often leaving sticky ends.

What is gel electrophoresis used for?

Answer: Separating DNA fragments by size; smaller fragments move farther through the gel toward the positive electrode.

What does PCR do?

Answer: Amplifies a specific DNA segment through repeated cycles of denaturing, annealing primers, and extension.

What is epigenetics?

Answer: Heritable changes in gene expression without changes to the DNA sequence, such as DNA methylation and histone modification.

What is the difference between a promoter and an enhancer?

Answer: A promoter is where RNA polymerase binds to start transcription; an enhancer is a distant sequence that increases transcription when bound by activators.

How does the lac operon work?

Answer: When lactose is absent a repressor blocks transcription; lactose (as allolactose) removes the repressor so the genes are expressed.

What is Mendel's law of segregation?

Answer: Each organism carries two alleles for a trait, and they separate during gamete formation so each gamete gets one.

What is a test cross and why is it used?

Answer: Crossing an organism with a dominant phenotype to a homozygous recessive to reveal whether it is homozygous or heterozygous.

What ratio results from a monohybrid cross of two heterozygotes (Bb × Bb)?

Answer: 3:1 phenotypic, 1:2:1 genotypic.

Genotype vs phenotype?

Answer: Genotype is the allele combination (e.g., Bb); phenotype is the observable trait (e.g., brown eyes).

What is the law of independent assortment?

Answer: Alleles of different genes assort independently during gamete formation.

What is a Barr body?

Answer: An inactivated X chromosome in female mammalian cells.

What is a karyotype?

Answer: An organized picture of all the chromosomes in a cell, used to detect chromosomal abnormalities.

What is nondisjunction?

Answer: Failure of chromosomes to separate properly during meiosis, producing gametes with extra or missing chromosomes.

What is genetic linkage?

Answer: Genes close together on the same chromosome tend to be inherited together.

What is a sex-linked trait and why are males more often affected?

Answer: A trait on the X chromosome; males have only one X, so a single recessive allele is expressed.

What is polygenic inheritance?

Answer: A trait controlled by many genes, producing continuous variation.

What is epistasis?

Answer: One gene's expression masks or modifies the effect of another gene.

What is pleiotropy?

Answer: One gene affects multiple phenotypic traits.

What is codominance?

Answer: Both alleles are fully expressed in the heterozygote.

What is incomplete dominance?

Answer: The heterozygote shows a blended, intermediate phenotype.