1. Warm-Up (2/4)
On the piece of white paper from the back, answer the following question.
Name
Date
Period
Describe an example of a mutation which is beneficial for the individual but deleterious for the individual’s offspring.

2. 1A.2c: Some phenotypic variations significantly increase or decrease fitness of the organism and the population.
Illustrative example: sickle cell anemia
3C.1d: Changes in genotype may affect phenotypes that are subject to natural selection. Genetic changes that enhance survival and reproduction can be selected by environmental conditions.
Illustrative example: Sickle cell disorder and heterozygote advantage
3C.1d.1: Selection results in evolutionary change.
4C.1b: Multiple copies of alleles or genes (gene duplication) may provide new phenotypes.
4C.1b.1: A heterozygote may be a more advantageous genotype than a homozygote under particular conditions, since with two different alleles, the organism has two forms of proteins that may provide functional resilience in response to environmental stresses.
4C.1b.2: Gene duplication creates a situation in which one copy of the gene maintains its original function, while the duplicate may evolve a new function.
Illustrative example: the antifreeze gene in fish

3. Genetic Variation in Natural Selection
Case in Point: the Hemophilia Mutation
Some variations are bad for the individual, good for the population.
From our dear friend, Wikipedia:
“HbS is produced by a point mutation in HBB in which the codon GAG is replaced by GTG. This results in the replacement of hydrophilic amino acid glutamic acid with the hydrophobic amino acid valine at the sixth position (6Glu→Val). This substitution creates a hydrophobic spot on the outside of the protein that sticks to the hydrophobic region of an adjacent hemoglobin molecule's beta chain. This further causes clumping of HbS molecules into rigid fibers, causing ‘sickling’ of the entire red blood cells in the homozygous (HbS/HbS) condition (Thom et al, 2013 CSH Persp Med).”
variation = mutation
HBB wild-type structure

4. Genetic Variation in Natural Selection
Case in Point: the Hemophilia Mutation
Some variations are bad for the individual, good for the population.
…so why hasn’t HBA been selected out of the human population?
Homozygous for HBS = sickle cell anemia
HBS allele
HBA (wild-type) allele
Homozygous for HBA = normal
Red blood cells collected from different individuals

5. Genetic Variation in Natural Selection
Case in Point: the Hemophilia Mutation
Some variations are bad for the individual, good for the population.
“The Heterozygote Advantage”
Homozygous for HBS = sickle cell anemia
Heterozygous for HBS and HBA = normal, and malaria resistant
Homozygous for HBA = normal

6. Critical Thinking Question #1
In a 2012 study published in the journal American Journal of Epidemiology, 171 newborn children not affected by malaria were tested every month for malaria. The proportion that continued to stay malaria-negative is plotted on the graph below over time. The solid line represents children heterozygous for the HBA allele, and the dashed line represents children homozygous for the wild-type allele. Assuming that all children affected by malaria died as a result,
explain how the genetic makeup of this population changed over time.

7. 1A.2c: Some phenotypic variations significantly increase or decrease fitness of the organism and the population.
Illustrative example: sickle cell anemia
3C.1d: Changes in genotype may affect phenotypes that are subject to natural selection. Genetic changes that enhance survival and reproduction can be selected by environmental conditions.
Sickle cell disorder and heterozygote advantage
3C.1d.1: Selection results in evolutionary change.
4C.1b: Multiple copies of alleles or genes (gene duplication) may provide new phenotypes.
4C.1b.1: A heterozygote may be a more advantageous genotype than a homozygote under particular conditions, since with two different alleles, the organism has two forms of proteins that may provide functional resilience in response to environmental stresses.
4C.1b.2: Gene duplication creates a situation in which one copy of the gene maintains its original function, while the duplicate may evolve a new function.
Illustrative example: the antifreeze gene in fish

8. Horizontal Transfer in Eukaryotes
Transposition of pieces of DNA occurs in eukaryotes
some chromosome
some other chromosome
“transposon”
“cut and paste” mechanism

9. Horizontal Transfer in Eukaryotes
“copy and paste” of transposons results in gene duplication
some chromosome
some other chromosome
“copy and paste” mechanism

10. Horizontal Transfer in Eukaryotes
More gene copies = more alleles =
more variation
can be an enzyme inside the cell,
or can break up ice outside the cell
SAS-A (original)

11. Horizontal Transfer in Eukaryotes
More gene copies = more alleles =
more variation
Enzyme inside the cell,
and doesn’t need to break up ice outside the cell
SAS-A (original)
Enzyme not inside the cell, instead breaks up ice outside the cell
SAS-A (original)

12. Horizontal Transfer in Eukaryotes
More gene copies = more alleles =
more variation
Enzyme inside the cell,
and doesn’t need to break up ice outside the cell
SAS-A (original)
Not gonna happen!
Need the enzyme, bro!
Enzyme not inside the cell, instead breaks up ice outside the cell
SAS-A (original)

13. Horizontal Transfer in Eukaryotes
What if the gene duplicated?
More gene copies = more alleles =
more variation
SAS-A (original)
SAS-B (duplicate)

14. Horizontal Transfer in Eukaryotes
More gene copies = more alleles =
more variation
Enzyme inside the cell,
and doesn’t need to break up ice outside the cell
SAS-A (original)
Enzyme inside the cell
Breaks up ice outside the cell
SAS-A (original)
SAS-B (duplicate)

15. Horizontal Transfer in Eukaryotes
Duplication allows variation!
More gene copies = more alleles =
more variation
Lost ability to break up ice
Lost ability to be an enzyme
SAS-A (original)
SAS-B (duplicate)

16. Horizontal Transfer in Eukaryotes
More gene copies = more alleles =
more variation
Enzyme inside the cell,
and doesn’t need to break up ice outside the cell
SAS-A (original)
Enzyme inside the cell
Breaks up ice outside the cell
SAS-A (original)
SAS-B (duplicate)
Antarctic Eeelpout

17. Critical Thinking Question #2
The ligand Dll1 promotes formation of vertebrae in the spine: species with high levels of Dll1 activity during development, such as snakes, develop more vertebrae and longer spines. Predict the effects of a duplication of the Dll1 gene on a population of giraffids, an extinct deer- like animal which depended on fruit hanging from trees for survival. (LO 3.24)

18. Closure
On the piece of white paper from the back, answer the following question:
Name
Date
Period
How did duplication of the SAS gene result in molecular variation of cellular function in eelpout fish?
Scale 1 – 10