Mendel and the Gene Idea
What did Mendel’s Law of Segregation state about alleles during gamete formation?
they separate so each gamete gets only one allele per gene
The SRY gene that triggers testes formation is located on which chromosome?
Y chromosome
Which four bases form DNA and which pair with which?
A pairs with T, G pairs with C
Which enzyme separates DNA strands and synthesizes RNA without a primer?
RNA polymerase
The initiation codon is _________ and codes for what amino acid?
AUG, methionine
In a monohybrid cross between two heterozygotes, what phenotypic ratio appears in the F₂ generation?
3:1 (dominant:recessive)
Why are males more likely to express X-linked recessive disorders?
they have only one X chromosome (hemizygous), no dominant allele to mask the recessive one.
What did the Meselson-Stahl experiment prove?
DNA replication is semiconservative (each new molecule has one old strand and one new strand)
In eukaryotes, the promoter region often contains what specific sequence recognized by transcription factors?
TATA box
What does tRNA do during translation?
brings specific amino acids to the ribosome by matching its anticodon to mRNA codons
What is the genotype of a true-breeding purple-flowered pea plant if purple is dominant (P) and white is recessive (p)?
PP
A female heterozygous for an X-linked gene can show a mosaic phenotype because of what process?
random X inactivation (Barr body formation)
DNA polymerase adds nucleotides to which end of a growing strand?
3′ end only (so new strand grows 5′ → 3′)
What direction is mRNA synthesized relative to the template DNA strand?
5′ → 3′ direction (antiparallel to template 3′ → 5′).
How many codons code for amino acids, and how many are stop signals?
61 for amino acids + 3 stop codons (UAA, UAG, UGA)
A plant with TtGg is crossed with ttgg. What fraction of offspring will be tall and green if T and G are dominant?
¼ (TtGg × ttgg → ½ tall × ½ green = ¼)
What is the term for offspring with non-parental phenotype combinations due to crossing over?
recombinants
The lagging strand is synthesized discontinuously as short segments called __________.
Okazaki fragments
What is the polyadenylation signal sequence and its function?
AAUAAA; signals RNA cleavage and addition of the poly-A tail to form mature mRNA
What is the purpose of the A, P, and E sites in the ribosome?
A = aminoacyl site (entry of tRNA)
P = peptidyl site (holds growing chain)
E = exit site (where tRNA leaves)
In Mendel’s dihybrid cross (YyRr × YyRr), what are the four phenotypes and their ratio?
9 yellow round:3 yellow wrinkled:3 green round:1 green wrinkled (9:3:3:1)
Match the syndrome to its chromosomal change: a. XXY, b. XO, c. trisomy 21.
a. Klinefelter syndrome
b. Turner syndrome
c. Down syndrome
During replication, what do primase and DNA ligase each do?
primase adds RNA primers to begin DNA synthesis, ligase joins Okazaki fragments into a continuous strand
Compare termination in prokaryotes vs. eukaryotes.
prokaryotes: RNA polymerase stops at terminator and mRNA is ready for translation
eukaryotes: RNA pol II passes AAUAAA, transcript cut and processed (post-transcriptionally)
Describe one difference in translation between prokaryotes and eukaryotes.
prokaryotes can translate while transcribing (no nucleus)
eukaryotes separate the two processes and modify mRNA before export.