inheritance

• Meiosis is a form of cell division that gives rise to genetic variation; its main role is the production of haploid gametes as cells produced by meiosis have half the number of chromosomes
• Reduction division in meiosis takes place where the chromosome number halves from diploid to haploid
• Meiosis produces genetically different cells through:

  • Crossing over of chromatids where pairs of chromosomes exchange genetic material
  • Independent assortment of chromosomes leading to various combinations of chromosome arrangement
• During fertilisation, the random fusion of gametes increases genetic variation in offspring
• Monohybrid crosses predict the ratios of inherited characteristics in a population, with outcomes having a ratio of 3:1 where the dominant trait is more common
• Dihybrid crosses determine the outcome of two genes, each with two alleles, resulting in 16 outcomes
• Albinism affects melanin production, leading to white hair, light eyes, and pale skin due to a mutation in the TYR gene affecting tyrosinase production
• Sickle cell anaemia results from a mutation in the HBB gene, altering hemoglobin production and causing crescent-shaped red blood cells
• Hemophilia, a sex-linked recessive disorder, results from a mutation in the FB gene causing a factor VIII deficiency
• Huntington's disease, a neurodegenerative disease, is caused by a mutation in the HTT gene affecting the production of huntingtin
• The chi-squared test is a statistical test used to establish if the difference between observed and expected results is significant or due to chance
• Mutations are changes in the sequence of nucleotides in DNA molecules, including insertion/deletion mutations, point mutations/substitutions, and nonsense mutations
• Mutations can cause frameshifts, point mutations/substitutions, nonsense mutations, missense mutations, and silent mutations
• Frameshift mutations occur after the insertion/deletion point, causing a shift in the sequence of nucleotides
• Point mutation/substitution replaces one base pair with another, which may have no effect
• Nonsense mutations stop translation early, leading to a truncated polypeptide due to a premature stop codon
• Missense mutations change a codon, resulting in a different amino acid and potentially altering the protein's tertiary structure
• Silent mutations change a codon without affecting the amino acid sequence produced
• Neutral mutations have no effect on the organism, such as those in non-coding DNA regions or silent mutations
• Beneficial mutations, like trichromatic vision in humans, can occur, while harmful mutations, like in the CFTR protein causing cystic fibrosis, are detrimental
• Gene expression can be controlled at transcriptional, post-transcriptional, translational, and post-translational levels
• Transcriptional control includes the lac operon in E.coli, where the binding of the repressor to the operator region inhibits structural gene transcription
• Transcriptional control can be influenced by glucose and lactose concentrations, affecting the lac operon's activity
• Post-transcriptional control involves editing the primary mRNA transcript by removing introns and leaving exons for protein production
• Post-translational control includes processes like adrenaline activation through cyclic AMP, which triggers a cascade of enzyme reactions
• Gibberellin, a plant hormone, controls plant growth by breaking down DELLA, a repressor protein, to allow gene transcription and increase amylase synthesis