Review for Genetics Lab final

  • Protein Sequence vs Nucleotide Sequence

    • Students often confuse nucleotide sequences with protein sequences.
    • Protein BLAST (Basic Local Alignment Search Tool) is used for comparing sequences.

  • Using Protein BLAST

    • Input the protein sequence into the central window of Protein BLAST.
    • Utilize the reference proteins database, specifically the "RefSeq Proteins" database for accurate results.
    • Leaving the organism input blank allows comparison against all known sequences, albeit a longer processing time.

  • Fly Base Introduction

    • The FlyBase database offers user-friendly access to genetic information.
    • Example Gene: "Lozenge" (lz)
    • Defined as a transcription factor.
    • Part of the RAD-related transcription factor family, crucial for eukaryotic gene expression regulation.

  • Gene Information

    • Location is significant: For the lozenge gene in Drosophila, it is X-linked on chromosome 1.
    • Genetic linkage is central to Mendelian inheritance.
    • Two linked genes will recombine less likely than unlinked genes.
    • Map units indicate distance between genes on chromosomes; e.g. genes 10 map units apart equate to a 10% recombination frequency.

  • Understanding Genetic Mapping

    • To find distance between genes:
    • Formula: \text{Distance} = \frac{\text{Number of Recombinants}}{\text{Total Offspring}} \times 100
    • Test cross analysis helps visualize potential offspring phenotypes.
    • Parentals: Original phenotypes, Recombinants: New phenotypes resulting from crossover.

  • Phenotype and Genotype Relationship

    • Utilize correct genotyping for accurate predictions: e.g. upper case for dominant traits.
    • Example for the taster phenotype:
    • Dominant (T) for taster, recessive (t) for non-taster.

  • Searching with BLAST

    • Returning results from BLAST requires proper identification of gene names as presented in results, including percentage of amino acid identity.
    • Finding orthologs (genes in different species) and paralogs (genes within the same species) is crucial in evolutionary studies.

  • Alternative Splicing

    • Genes like lozenge can produce multiple isoforms through alternative splicing, altering protein function.
    • Example: Lozenge has two isoforms due to splicing differences.

  • Population Genetics

    • Understand key definitions and formulas for allele frequencies within populations.
    • Example: Hardy-Weinberg equilibrium where p + q = 1 ; and p^2 + 2pq + q^2 = 1 for genotype frequencies.

  • Tetrad Analysis

    • Yeast tetrad analysis provides insight into meiotic events. Important for understanding genetic recombination.

  • Summary of Mendelian Genetics

    • Knowledge of genetic linkage, gene mapping, and gene function is essential for genetic predictions and experiments.
    • Proper notation is crucial for clarity in genetic crosses and predictions.