BIOA01 TERM TEST 2 -- BLOCK 5

Genes located close together on the same chromosome that tend to be inherited together during meiosis because they travel as a single physical package.

What are linked genes?

Crossing over (homologous recombination) during Prophase I of meiosis.

What is the biological process that breaks genetic linkage between linked genes?

1 map unit (m.u.) or 1 centimorgan (cM).

What does 1 percent recombination frequency ($RF$) equal in genetic mapping?

A point mutation where a nucleotide changes, but the resulting codon still codes for the exact same amino acid due to the redundancy of the genetic code.

What is a silent mutation?

A point mutation that results in a codon coding for a different amino acid.

What is a missense mutation?

A point mutation that changes a normal amino acid codon into a premature stop codon, resulting in a shortened protein.

What is a nonsense mutation?

An insertion or deletion of nucleotides in numbers not divisible by three, which completely shifts the reading frame of translation.

What is a frameshift mutation?

A type of gene interaction where the alleles of one gene mask or suppress the phenotypic expression of a completely different gene.

What is epistasis?

Traits that show a continuous, bell-curve range of variation across a population because they are controlled by the additive effects of multiple genes.

What are quantitative (polygenic) traits?

By dividing the number of recombinant offspring by the total number of offspring and multiplying by 100.

How do you calculate recombination frequency ($RF$)?

8 map units (or 8 centimorgans) apart.

Gene A and Gene B have a recombination frequency of 8%. How far apart are they on the chromosome?

It approaches 50%, making them behave as if they assort independently just like unlinked genes.

If two genes are located very far apart on the same chromosome, what is their expected recombination frequency?

It is a silent mutation with no effect on the protein sequence.

A DNA sequence undergoes a point mutation where AAG (Lysine) changes to AAA (Lysine). What type of mutation is this, and what is its effect on the protein?

A missense mutation (specifically a non-conservative substitution).

A DNA sequence undergoes a point mutation that changes a codon from GAG (Glutamic acid) to GUG (Valine), altering protein folding (such as in sickle-cell anemia). What type of mutation is this?

It causes a frameshift mutation, scrambling the reading frame and all downstream amino acids, usually producing a completely nonfunctional protein.

An insertion of 2 base pairs occurs near the beginning of a gene's coding region. What happens to the resulting mRNA and protein?

Because there is very little physical space between them, making it statistically rare for a crossover event to occur precisely in that interval.

Why do genes that are extremely close together on a chromosome exhibit very low recombination frequencies?

A modified 9:4:3 ratio.

In a cross involving two epistatic genes controlling coat color in Labrador retrievers, an allele at one locus completely blocks pigment deposition regardless of the alleles at the black/brown locus. What phenotypic ratio typically modified from 9:3:3:1 is observed in the F2 generation?

Because the trait is determined by the cumulative, additive effects of multiple genes working together alongside environmental influences.

Why do polygenic traits display a smooth, bell-shaped phenotypic distribution curve rather than discrete categories?

15 m.u. (map units are additive over short distances).

If a genetic map shows that Gene X and Gene Y are 5 m.u. apart, and Gene Y and Gene Z are 10 m.u. apart (with Y lying between them), what is the expected map distance between Gene X and Gene Z?

20% (40 / 200 = 0.20 x 100).

During a testcross for two linked genes, a researcher counts 40 recombinant offspring out of 200 total offspring. What is the recombination frequency?