Introduction to genetics

Question 1

What is a locus?

Answer 1

The site of a gene on a chromosome.

Question 2

What does a gene contain?

Answer 2

A sequence of base pairs that code for a particular product.

Question 3

What is transcription?

Answer 3

The first stage of protein synthesis, involves the creation of a single-stranded mRNA copy of the DNA coding strand.

Question 4

What happens during transcription?

Answer 4

• The double helix unwinds and unzips.
• Free activated mRNA nucleotides bind via hydrogen bonds to the exposed bases of the template strand.
• Follow base pairing rules of A-U and G-C.
• Catalysed by RNA polymerase

Question 5

What is trranslation?

Answer 5

The second stage in protein synthesis, involves the assembly of polypeptides at ribosomes.

Question 6

What happens during translation?

Answer 6

• The sequence of codons dictate the sequence of amino acids.
• The chain of amino acids makes a specific polypeptide.

Question 7

What are codons?

Answer 7

Triplets of nucleotide bases which code for an amino acid.

Question 8

What is transfer RNA?

Answer 8

• Made in nucleus and passes into cytoplasm - lengths of RNA folded into hairpin shape.
• Has 3 exposed bases at one end (anticodon) where amino acids can bind.

Question 9

How is transfer RNA used?

Answer 9

To fetch amino acids required to synthesise protein.

The anticodon binds temporarily to its complementary codon on the mRNA strand.

Question 10

How is a polypeptide assembled?

Answer 10

1. mRNA binds to a ribosome, where 2 codons are attached to a small subunit of the ribosome and exposed to the large subunit.
2. A different amino acid tRNA binds to the 2nd exposed codon.
3. A peptide bond is formed between the amino acids.
4. The ribosome moves along the mRNA, reading the codons with tRNA connecting the correct amino acids and forming more peptide bonds.
5. The polypeptide continues to grow until the stop codon is reached (no corresponding tRNA).

Question 11

What did Mendel research?

Answer 11

Peas - 7 traits each with 2 characteristics.

Question 12

What does Mendel’s first law state?

Answer 12

Segregation:

- Dominant/recessive alleles segregate during reproduction

Question 13

What does Mendel’s second law of inheritance state?

Answer 13

Independent assortment:

- Each trait sorts independently.

Question 14

What phenotype and genotype ratios does a dihybrid cross of AaBb and AaBb produce?

Answer 14

Phenotype: 9:3:3:1
Genotype: 4:2:2:2:2:1:1:1:1

Question 15

In what instances do genes not follow Mendelian laws?

Answer 15

1. X chromosome (some recessive most prevalent in males, e.g. haemophilia)
2. New mutations
3. Complex traits e.g. sz and depression.

Question 16

What did Caspi et al (2005) find when comparing the % of 26yos w/sz compairing cannabis and non-users with different genotypes?

Answer 16

Met/Met = 4% both groups
Val/Met = 2-3% in non-cannabis users, 6% users
Val/Val = 2% non, 13% users.