Transcript
Evolution: Genetics
Mr. KastelerZoologyDay 22
The Standards:
• 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
Basic Genetics
• Brief review: • What is DNA?• How many nucleotide bases are
there?• Which ones pair together?
Some more important definitions:
• GENOTYPEGENOTYPE: the actual GENES (technically, ALLELES) an organism has
• PHENOTYPEPHENOTYPE: the PHYSICAL CHARACTERISTIC exhibited by the organism
• HOMOHOMOZYGOUSZYGOUS: when an organism has two identical (the SAMESAME) alleles
• HETEROHETEROZYGOUSZYGOUS: when an organism has two differentdifferent alleles
• Dominant & Recessive…
• Ex. Mendel’s Peas…
A few definitions you just gotta know…
• A GENEGENE is a location on your DNA is a location on your DNA that codes for a physical trait (i.e. height, hair color, eye color)
• An ALLELEALLELE is a form of a gene is a form of a gene coding for a given trait (i.e. tall, short, blonde, brunette, blue eyed, brown eyed, etc.)
Basic Inheritance
• What’s inheritance?• Let’s talk about basic inheritance patterns
• Animals have varying numbers of chromosomes…
• Background CFU: What’s a chromosome?Background CFU: What’s a chromosome?• A chromosome is bundled up DNAA 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?
Mendel’s Peas:
• 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.
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
Genetic Variation• 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 homogeneoushomogeneous, 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
• Genetic Mutations • Genetic Recombination• Gene Flow (Immigration &
Emigration)• Genetic Drift
Genetic Mutations
There are two main types of genetic mutations you need to know:
1. Point Mutation2. Frame Shift Mutation
• Insertion• Deletion
Point Mutation
• This is where a single base pair is changed
• Example: The dog bit the cat• Point Mutation: The dog bit the car• 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?
Let’s Discuss…
• What is worse- a deletion or an insertion? Why?• Answer: Deletion
Genetic Recombination
• This occurs during meiosis• Meiosis: formation of sex cells
• Recombination/Crossing Over is when two gametes exchange pieces of genetic information
Genetic Recombination
• The gamete genotypes went from aa AA… (homozygous)
…to aA aA(heterozygous)
• X =
Gene Flow
• Genes flow into the gene pool when new individuals are added to the population through IMMIGRATION• INCREASES GENETIC VARIATION
• Genes flow out of the gene pool when individuals leave the population through EMIGRATION• DECREASES GENETIC VARIATION
Genetic Drift
• Think: CHANCE• 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
Genetic Drift
• 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)?
• **FOUNDER EFFECT & Islands**• **Bottleneck Effect**
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