The roles of genes in
7 flashcards to master this topic
Define the terms 'gene', 'locus', and 'allele'.
A gene is a heritable factor that controls a specific trait. The locus is the specific location of a gene on a chromosome. An allele is a variant form of a gene at a particular locus; different alleles code for different variations of the same trait.
Explain the difference between dominant, recessive, and codominant alleles.
A dominant allele expresses its phenotype even in the presence of a recessive allele. A recessive allele only expresses its phenotype when homozygous. Codominant alleles both contribute to the phenotype when heterozygous, resulting in a combined or intermediate trait.
Define 'genotype' and 'phenotype'.
Genotype refers to the genetic makeup of an organism for a specific trait (
What is the purpose of a test cross, and how is it performed?
A test cross is used to determine the genotype of an individual showing the dominant phenotype. It involves crossing the individual with a homozygous recessive individual. The offspring phenotypes reveal the genotype of the unknown parent (
Explain the concept of sex linkage.
Sex linkage refers to genes located on sex chromosomes (X or Y in humans). Traits controlled by these genes show different inheritance patterns in males and females because males have only one X chromosome.
Define autosomal linkage.
Autosomal linkage refers to genes located on the same autosome (non-sex chromosome) and are therefore inherited together unless separated by crossing over during meiosis. Linked genes do not assort independently and will deviate from the expected Mendelian ratios in dihybrid crosses.
What is epistasis?
Epistasis is the interaction of genes where one gene masks or suppresses the expression of another gene at a different locus. This alters the expected phenotypic ratios in a dihybrid cross.
Explain how to calculate the chi-squared (χ²) value and what it indicates.
The chi-squared (χ²) value is calculated using the formula: χ² = Σ [(O - E)² / E], where O is the observed frequency and E is the expected frequency. It measures the difference between observed and expected results; a high value suggests a statistically significant difference, while a low value suggests the differences are due to chance.
What is the relationship between a gene, a protein, and a phenotype?
A gene contains the DNA sequence that codes for a specific protein. The protein produced then influences the observable characteristics (phenotype) of an organism. A mutation in a gene can alter the protein, leading to a different phenotype.
Explain the genetic basis of albinism, referencing the TYR gene and tyrosinase.
Albinism is often caused by a mutation in the TYR gene, which codes for the enzyme tyrosinase. Tyrosinase is essential for melanin production. A non-functional tyrosinase enzyme, due to a mutation in the TYR gene, results in reduced or absent melanin, leading to albinism.
Describe the molecular basis of sickle cell anaemia, linking the HBB gene to haemoglobin.
Sickle cell anaemia is caused by a mutation in the HBB gene, which codes for a subunit of haemoglobin. This mutation leads to the production of abnormal haemoglobin, causing red blood cells to become sickle-shaped. These cells can block blood vessels and reduce oxygen delivery.
Explain how a mutation in the F8 gene can lead to haemophilia.
Haemophilia is often caused by a mutation in the F8 gene, which codes for factor VIII, a protein essential for blood clotting. A mutation in the F8 gene can result in a non-functional or deficient factor VIII, impairing the blood clotting process.
Describe the genetic cause of Huntington's disease, referring to the HTT gene and huntingtin protein.
Huntington's disease is caused by an expanded CAG repeat within the HTT gene. This mutated HTT gene produces an abnormal huntingtin protein with an elongated polyglutamine region, which causes the protein to misfold and aggregate, leading to neuronal damage.
What is the role of gibberellin in stem elongation?
Gibberellin is a plant hormone that promotes stem elongation. It does this by stimulating cell division and cell elongation in the stem. The concentration of gibberellin affects the rate of stem growth.
Explain the roles of the Le and le alleles in the gibberellin synthesis pathway and their effect on stem length.
The dominant Le allele codes for a functional enzyme in the gibberellin synthesis pathway, leading to normal gibberellin production and stem elongation. The recessive le allele codes for a non-functional enzyme, resulting in reduced gibberellin synthesis and shorter stems.
Ready to test yourself?
Practice with MCQ questions to check your understanding of The roles of genes in.
Take QuizStudy Mode
Rate each card Hard, Okay, or Easy after flipping.