Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A gene is a heritable factor that consists of a length of and influences a specific characteristic.
A gene occupies a specific position on a chromosome called the .
Alleles are alternative forms of a gene that differ from each other by only one or a few bases.
New alleles are formed by mutation, specifically base substitution mutations where one base in the sequence of a gene is replaced by a different base.
The genome is the whole of the genetic information of an organism. For humans, this consists of billion base pairs across chromosomes.
The Human Genome Project () was an international cooperative venture established to sequence the entire human genome ( base pairs).
In sickle cell anemia, a mutation in the gene results in the substitution of adenine for thymine ( to ), leading to the replacement of glutamic acid with valine in the -globin polypeptide.
📐Formulae
💡Examples
Problem 1:
Calculate the probability of an offspring being a carrier for a recessive genetic disorder if both parents are heterozygous ().
Solution:
The probability is or .
Explanation:
Using a Punnett square for a cross between and , the possible genotypes are and . The carriers are the heterozygotes ( and ), which represent out of possibilities: .
Problem 2:
Explain the molecular cause of Sickle Cell Anemia using the base substitution mutation of the allele.
Solution:
The mutation occurs on the codon of the gene: .
Explanation:
During transcription, the codon changes from to . This results in the translation of Valine instead of Glutamic Acid. Valine is hydrophobic, which causes the hemoglobin molecules to aggregate under low oxygen conditions, distorting the cell into a sickle shape.