Red-eyed and white-eyed Drosophila
Not all mutation are equal!
Q: what mutation will likely have the greatest deleterious effect?
A: C → Ain intron 1 :
- however if changes message for where supposed to splice out, can be bad
B: C → G mutation in the promoter
C: tryptophan → stop codon mutation in first intron: we know for sure gonna stop
D: typ → stop codon in last exon
- if changes shape
• Wild-type: the “normal” or most common form– reference strain
• Mutants: variants of the wild-type form
• Genotype: Genetic composition Phenotype:Ameasurable character
• Allele: One of the different forms of a gene that can exist at a single locus
• Gene locus: The specific region on a chromosome where the gene is located
• Diploid: having two chromosome sets
• Haploid: having one chromosome set
• Homozygous: carrying a pair of identical alleles at one locus
◦ eg. m/m or +/+ or A/a
• Heterozygous: carrying a pair of different alleles at one locus
◦ Eg. A/a or M/m
• Dominant:An allele that expresses its phenotypic effect even when heterozygous with a
◦ thus, if Ais dominant over a, thenA/AandA/a have the same phenotype.(gives rise to a
• Recessive:An allele whose phenotypic effect is not expressed in a heterozygote. If a is
recessive, then you will only observe the phenotype when homozygous: a/a. (gives rises to a
→ the genetic differences among individuals
→ most people (except for identical twins*) do not share the same sequence of DNA.
How does variation arise?
1. During Meiosis the random mixing of maternal and paternal chromosomes. The union of which egg
and sperm is also random*.
Variation arises by mutation:
1. Spontaneous (i.e. mistakes in replication)
2. Genetic variation can be produced in the laboratory by using high-energy radiation or chemicals to
* some caveats: not actually random, sperm all different → fastest largest sperm reach egg first Gene regulation is important!
• the genome of in the nuclei of the 50 trillion cells is the roughly identical but we have so many
different cell types
• not all genes are expressed (turned on ) in every cell
• muscle cells turn on muscle specific genes
• neurons turn on neuronal specific genes
• eye cells must turn on the right genes to build and eye
• genes regulation is important for all aspects of development, (not just making different types of
cells) eg.cell division, cell movements, pattern formation, organ and tissue formation.
• messing up genes (mutations) and/or how they're regulated