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Heredity Misconceptio
nsHaving misconceptions is actually a good thing – it means that you’ve been thinking! However, it’s time to unlearn a few things …
Misconception 1: Genes code for traits
ACTUALLY … Genes are instructions for building proteins, which have major affects on traits.
Misconception 2: Genetics Determine Who I Am
ACTUALLY …Remember GATTACA!Genes code for proteinsEnvironment, choices have huge effects!
Misconception 3: Most Traits Are Controlled by a Single Gene
ACTUALLY … multiple proteins can affect this phenotype
E.g. eye color is controlled by at least 2 genes and is probably affected by many more
Misconception 4: There are only 2 alleles for each gene, dominant and recessive
There can be many different alleles for each gene
E.g. blood type, there is the IA allele, IB allele and i allele.
Misconception 5:Dominant Alleles Are More
Common Not true at all Examples: 6 fingers, a certain type of
dwarfism, Huntington’s Disease, Why might a dominant trait be really
rare?
Misconception 6:Dominant Alleles Are
BetterMost genetic diseases tend to be
recessiveWhy would dominant lethal diseases
tend to disappear rather quickly?But in general a trait being
dominant DOES NOT in any way mean it is better
Misconception 7:There is a Gene for Diseases
Diseases are mostly the result of mutated alleles for necessary genes
Thus the person does not produce a necessary protein, or produces a deformed protein
Misconception 8: Dominant Alleles Shut Off
Recessive Alleles The alleles are on separate
chromosomes and do not interact with each other at all
I’m going to talk about what REALLY happens for your own piece of mind/knowledge/trivia – not for the quizzes (next slide)
What Actually HappensSome alleles are instructions for producing functional proteins
The other alleles produce no protein at all or a protein that does not function at all
A trait is dominant ifOne set of instructions produces enough proteins to have the trait
I.e. if you are heterozygous you have the trait
A trait is recessive ifOne set of instructions is not enough to cause the trait
I.e. if you are heterozygous you will not have the trait
Incomplete Dominance
Heterozygotes produce fewer proteins, so they have an intermediate phenotype
Ex: flower color is “new” color. Heterozygous (Red allele & white allele) = Pink
Co-DominanceMultiple alleles produce functional
proteins pretty equally…Ex: Black chicken (BB) and white
chicken (WW) = heterozygous (BW) is a speckled black and white chicken
Also blood type! AB blood both proteins show up on the blood cell. O is simple dominance…just FYI. Blood type has 2 types of inheritance!
Male v. FemaleMales XYFemales XX
What This Means
Males have only one copy of genes on the X chromosome
Females have two X chromosomes
For Your Future Trivia Needs
XY system is only really in mammals
Some other fascinating sex determination systems
Birds and Some ReptilesZW system – females are ZW, males are ZZ
Kind of similar to our system, except roles are reversed
The egg determines the sex
In BeesMales have half as many
chromosomes If egg is fertilized, it becomes a
female, if it is not fertilized it grows into a male
In Some Reptiles (alligators) Temperature the egg is incubated at
determines sex Temperature seems to turn on or off
certain enzymes
In Some Fish (clownfish) The largest member of a school
becomes the reproductive female The next in line is the reproductive male All others are non-reproductive
When Nemo’s mother died he would have become a man… because his dad would have become a woman…
Parthenogenesis (asexual) Some animals lay eggs that require no
fertilization Interestingly in these snakes individuals
still “mate” with each other, even though there is no exchange of DNA, before laying eggs
Not really having sex, just dancing
Hermaphroditic Snails and Slugs
Have male and female anatomies
But reproduce with others, not with themselves
This video will blow your mind!
https://www.youtube.com/watch?v=wG9qpZ89qzc
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