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Variation among individuals - Coggle Diagram
Variation among individuals
Why do humans seem to have more variation than other species?
Coefficient of Variation (CV)
the ratio of the standard deviation of the mean
a measure of relative variability
shows the extent of variability in relation to the mean of the population
Proteins
different kinds of cells are distinguished by the proteins they make
for example: hemoglobin, mucigen, rhodopsin
Variation in Genetic Material
chromosomes
definition: thread-like structure made up of DNA
Locus: physical location of a gene on a chromosome
differences among individuals that are encoded in the genome and transmitted from parents to offspring
Example: variation in perception of taste
taste receptor proteins have diverse shapes and chemical properties; these bind with a subset of the chemicals in food
taste receptor cell sends nerve impulses to the brain, which integrates the messages
Ex: genetic variation for bitter taste perception
receptors for bitter flavor:
TAS2Rs
receptor that binds PTC is TAS2R38 encoded by a gene on chr. 7
there are three places where different versions of the TAS2R38 gene encode different amino acids
most common alleles: AVI and PAV
Ability to taste bitter flavors are transmitted from parents to offspring
the ability to taste PTC varies significantly from one population to another worldwide
combinations of alleles for this gene determine whether someone finds PTC intensely bitter, somewhat bitter, or without taste at all
Environmental Variation
differences among individuals due to exposure to different environments
Example: Water Flea (prey) and Phantom Midges (predator)
Water fleas...
have morphology, physiology, and behavior that can have changes triggered by environmental cues
reproduction:
use sexual reproduction when conditions deteriorate
make clones under favorable conditions
armor:
water flea can develop anti-midge armor only when midges are present
Inducible Defense: adaptive trait that helps in evading predation and only develops in the presence of a cue coming from the predator
metabolically expensive
changes in gene expression can be measured by quantifying production of mRNA
Genotype by Environment Interaction
differences among individuals encoded in the genome, in the way the environment influences phenotype
Example: Leopard gecko sex determined by temperature
changes in the production of a variety of proteins
reaction norm: set of phenotypes that can be produced by an individual genotype when exposed to different environmental conditions
genotype by temperature interaction
New Alleles
Arise from alterations to existing alleles
complementary base pairing provides a mechanism for copying the hereditary material
each strand then serves as a template for duplication of the other
two identical double-stranded DNAs
DNA polymerase: catalyze the synthesis of DNA
mutations creating new alleles can arise as a result of alterations to DNA (errors)
Mutations can...
prevent introns from being excised
many genes have intervening sequences called introns
coding sequences are called exons
introns are transcribed into mRNA but must be spliced out before translation
mutations in splice sites can prevent introns from being excised, resulting in production of abnormal proteins
alter protein function
Where new genes come from
gene duplication: one or more copies of a DNA segment is produced
Types:
retroposition: transcribed and spliced mRNA are reverse-transcribed and inserted into new genomic positions
Example: gene responsible for chrondosplaysia
comparing genome for differences between breeds with and without chrondosplaysia
located on Chromosome 18 is a duplicate copy of gene for fibroblast growth factor 4 (fgf4), which lacks introns and is located some distance from the parent copy
unequal crossing over: error in the genetic recombination during meiosis
substantial fraction of the genomic variation among individuals
genome is more affected be duplicated genes compared to differences resulting in point mutations
has generated families of functionally related genes
duplication followed by divergence in function generates gene families
substrate for adaptive evolution
New genes from Scratch
Accounts for much less than gene duplication
appear through modifications from noncoding DNA
Example: C22orf45
a gene of unknown function that is unique to humans
became a coding gene in the lineage leading to modern humans
Chromosome mutations
inversions: a type of chromosome rearrangement where a segment of a chromosome gets flipped around
section of DNA breaks away from chromosome