SC.912.L.15.15 Describe how mutation and genetic recombination increase genetic variation
SC.912.L.15.14 Discuss mechanisms of evolutionary change other than natural selection such as genetic drift and gene flow
What is DNA?
How many nucleotide bases are there?
Which ones pair together?
Some more important definitions:
GENOTYPE : the actual GENES (technically, ALLELES) an organism has
PHENOTYPE : the PHYSICAL CHARACTERISTIC exhibited by the organism
HOMO ZYGOUS : when an organism has two identical (the SAME ) alleles
HETERO ZYGOUS : when an organism has two different alleles
Dominant & Recessive…
Ex. Mendel’s Peas…
A few definitions you just gotta know…
A GENE is a location on your DNA that codes for a physical trait (i.e. height, hair color, eye color)
An ALLELE is a form of a gene coding for a given trait (i.e. tall, short, blonde, brunette, blue eyed, brown eyed, etc.)
Let’s talk about basic inheritance patterns
Animals have varying numbers of chromosomes…
Background CFU: What’s a chromosome?
A chromosome is bundled up DNA
These are chromosomes…
How many chromosomes do you have?
how many do you have?
46! … How many from Dad? From Mom?
What’s the genotype for a female? Male?
The brief synopsis: Gregor Mendel (the Father of Genetics) did experiments on pea plants. Some of them were tall (Is this a genotype or phenotype?) and some of them were short (Is this a genotype or phenotype?). He found that some of his tall plants were TT while others were Tt, with T coding for Tall and t coding for short (Is this a genotype or phenotype?). All of his short pea plants were tt (Is this a genotype or phenotype?) He crossed plants with different genotypes to see what kinds of phenotypes the offspring would exhibit. He developed Punnett squares.
Hopefully, we’ve all dealt with punnett squares in previous biology classes… but if not…here’s a quick reminder of how you set them up.
Punnett Square Set Up
You put the trait alleles of one parent across the top, and the trait alleles of the other parent down the side.
An allele is a gene coding for a given trait (i.e. tall, short, blonde, brunette, blue eyed, brown eyed, etc.)
This can get tricky with complicated variable genetic traits, such as eye color
The Basics: Gender Alleles
What is the likelihood that this couple will have a boy? A girl?
A little reminder of where you came from…
So, we get half of our genome from Mom, and half of our genome from Dad.
How much of your Dad’s genome will your children get?
This will help us determine relatedness for the next unit on animal behavior
Just as biodiversity increases the stability of an ecosystem, greater genetic variation improves the genetic stability of a population
More potential alleles means a higher likelihood that one or more individuals carry genes that could adapt to a new environment
When a population becomes too homogeneous , they are susceptible to genetic disorders and disease
Think… this is why it’s not a good idea to marry your brother or sister… or cousin
DIFFERENT is GOOD
When two individuals with similar genomes mate, they have a higher likelihood of passing down a recessive, deleterious (harmful) trait and having that trait expressed in the offspring
Ways to vary the Gene Pool
Gene Flow (Immigration & Emigration)
There are two main types of genetic mutations you need to know:
Frame Shift Mutation
This is where a single base pair is changed
Example: The dog bit the cat
Point Mutation: The dog bit the ca r
NOTICE: The severity of the mutation depends on the exact place of the change, not necessarily whether the mutation occurs earlier or later in the gene
It’s like a schedule change that just swaps one class for another, same period
Frame Shift Mutations
An insertion occurs when a base pair is inserted into the genome, shifting the genetic reading frame
Example: The dog mbi tth eca t
*Notice: The gene is fine upstream (before) of the mutation
It’s like a schedule change that alters one class… and messes up your whole schedule
Frame Shift Mutations
A deletion occurs when a base pair is deleted from the genome, also shifting the genetic reading frame
Example: The dob itt hec at
*Notice: Again, the gene is fine upstream of the mutation
What do you think is more serious, a mutation in the earlier part of the gene or later on? Why?
What is worse- a deletion or an insertion? Why?
This occurs during meiosis
Meiosis: formation of sex cells
Recombination/Crossing Over is when two gametes exchange pieces of genetic information
The gamete genotypes went from aa AA… (homozygous)
… to aA aA
Genes flow into the gene pool when new individuals are added to the population through IMM IGRATION
INCREASES GENETIC VARIATION
Genes flow out of the gene pool when individuals leave the population through EM IGRATION
DECREASES GENETIC VARIATION
Genetic Drift occurs when the allelic frequency within a population changes due to chance sampling from the gene pool
It is particularly potent in SMALL populations
Example: If I flip a coin 10,000 times, how many times would I get heads? Tails?
If I flip the same coin 10 times, how many times will I get heads? Tails?
Which example has a higher likelihood of being wrong (especially in percent)?