Download Population Dynamics Model Checklist

Biology 160, Unit 4, Discourse 3, version 03, CS
Name: __________________________________________________________Date: _________________
Checklist for Modeling Microevolution in a Human Population: Draft DUE Tuesday, Nov 27, 2012
As we did last time, everyone is going to do their own models as homework. Remember to just whip out a few
pieces of regular sized paper, a pencil, and create your story.
In this model you will concentrate on telling a story of how a human population evolves through natural
selection to develop resistance to malaria. Tell it as you would tell a colleague interested in how this aspect of
biology works. The objective of the model is to help you to learn how microevolution works by examining
individual variation, patterns of inheritance, population growth, environmental resistance, and population
genetics by telling a story. Use the information from your text and our in-class activities as evidence to
construct your explanation.
One suggestion of how your story might flow is written below. Use this as a guide to write your story in
both pictures and words.
1) ABSTRACT: Write a short paragraph that summarizes how resistance to malaria in a human population can
occur through natural selection of the sickle-cell allele. Use the “Identifying Parts of a Good Explanation of
Natural Selection” (IPGENS) worksheet as your guide. This initial paragraph is called an “abstract” and serves
as a summary of your model to help orient your readers to what you will be explaining more about. This will
also serve as your evidence-based explanation. (5 points)
 Make sure you include all seven parts outlined in the IPGENS worksheet in your explanation.
o Overproduction
o Environmental pressure/competition
o Pre-existing individual variation
o Heritable traits
o Happens over generations (time)
o Happens in populations (not a single individual)
o Offspring must be viable and fertile
Level of Evidence-Based Explanation:
Level 1
Level 2
(1 point)
(3 points)
Level of Evidence-Based Explanation rubric:
Level 1 (1 point)
Level 2 (3 points)
o Student describes what happens
o Student describes how or partial
o
o
in each part of the model without
linking them together to explain
how or why a human population
evolves resistance to malaria.
Student describes, summarizes, or
restates each part of the checklist
without making a connection to
full causal story.
No references to established
theories or evidence from lab or
the text are used.
o
o
why a human population evolves
resistance to malaria.
Student links together some parts
of the model but not all.
Student addresses theoretical
components tangentially (nonspecifically) or does not reference
evidence from lab and the text in
their explanation.
Level 3
(5 points)
Level 3 (5 points)
o
o
o
Student explains why a human
population evolves resistance to
malaria.
Student can trace a full causal
story for why a phenomenon
occurred. This is well supported
by diagrams in the model.
Student uses powerful science
ideas like the theory of natural
selection and Mendelian
inheritance, and references to
evidence from lab and the text, to
explain observable events.
Biology 160, Unit 4, Discourse 3, version 03, CS
2) INTRODUCTION: This brief section introduces our question: HOW MIGHT A POPULATION OF
HUMANS HAVE GAINED RESISTANCE TO MALARIA INFECTION?
Give your readers a brief introduction to what malaria infection and the sickle-cell resistance allele are.
 INTRODUCE: The Environmental Pressure – Malaria infection in humans. (1 point)
Draw/write an introduction to your explanatory model. Be sure to include:
A) A very simple (in other words spend little time on this part!) diagram that introduces the malaria lifecycle. No need to worry about the technical names for the various forms of the malarial parasite, but do
include
 its transmission from mosquito to human
 that malaria parasites spend part of their life-cycle in human red blood cells, and
 its transmission from human to mosquito that completes the cycle.
 INTRODUCE: The sickle-cell allele and phenotype. (2 points)
B) A diagram that explains the molecular biology of the sickle-cell allele. Be sure to include:
 How the DNA sequence of the sickle-cell allele compares to the normal hemoglobin allele.
 How the protein product of the sickle-cell allele (hemoglobin S) compares to the normal hemoglobin
allele (hemoglobin A)
 How the phenotype of sickled red blood cells compares to normal red blood cells.
 How sickled red blood cells affect the growth of malaria compared to normal red blood cells.
3) NATURAL SELECTION: HOW MIGHT MALARIA RESISTANCE HAVE BEEN SELECTED FOR
IN A POPULATION OF HUMANS? Draw a model showing the relative frequency of the sickle-cell allele in
a human population at three different time points: Time 0 (before selection by malaria), Time 1 (when this
population comes into contact with malaria), and Time 2 (after many, many generations of contact with
malaria). Use a pictorial representation for this purpose (like our in-class HIV drug resistance model), where a
circle represents a human, two lines inside the circle represent a pair of homologous chromosomes, and an “X”
represents the sickle-cell allele. (4 points)




Graphic makes clear that a population of humans is present.
Graphic makes clear that the human population is diploid.
Graphic makes clear that the sickle-cell allele is present in the population BEFORE selection.
Graphic makes clear that the sickle-cell allele is selected for in the population AFTER contact with
malaria
 Graphic makes clear that the genotypes can be homozygous normal allele, heterozygous, and
homozygous sickle-cell allele.
 Graphic makes clear that continuous selection happens over generations in a population
4) EVIDENCE FOR NATURAL SELECTION: OVERPRODUCTION AND POPULATION GROWTH.
HOW MIGHT MALARIA AND MALARIA RESISTANCE HAVE AFFECTED THE GROWTH OF
THIS POPULATION OF HUMANS? Draw a graph to represent the relative growth of this human population
from Time 0 to Time 2. (3 points)




Graph shows time on the X-axis and number of people on the Y-axis.
Graph logically shows what would happen to the relative population level at each time point.
Graph shows that selective pressure from environment takes place from Time 1 to Time 2.
A brief statement as to whether this graph is most like the exponential growth rate model or the logistic
growth rate model and why.
Biology 160, Unit 4, Discourse 3, version 03, CS
5) EVIDENCE FOR NATURAL SELECTION: PRE-EXISTING GENETIC VARIATION.
HOW MIGHT MALARIA RESISTANCE HAVE ARISEN IN THIS POPULATION OF HUMANS?
Draw/describe the mechanisms that gave rise to the genetic variation in the human population. Be sure to
include: (6 points)
 Random mutation in gametes
o types of possible mutations
 base substitutions
• silent
• missense
• nonsense
 insertions and deletions
• reading frame
 Sexual recombination
o meiosis
 meiosis I (separation of homologous chromosomes)
• prophase I
o crossing over
• metaphase I
o independent assortment of chromosomes
• anaphase I
• telophase I and cytokinesis
 meiosis II (separation of sister chromatids)
• prophase II
• metaphase II
• anaphase II
• telophase II and cytokinesis
 plasma membrane
 nuclear membrane
 chromatin
 sister chromatids
 centromeres
 spindle
 centrosomes
 tetrad
 chiasma
 diploid
 haploid
 chromosomes
o random fertilization
Biology 160, Unit 4, Discourse 3, version 03, CS
6) EVIDENCE FOR NATURAL SELECTION: HERITABLE TRAIT.
HOW MIGHT THE GENE FOR MALARIA RESISTANCE HAVE BEEN INHERITED IN THIS
POPULATION OF HUMANS?
At Time 2, as the frequency of heterozygous individuals is increasing, the probability that two heterozygous
individuals will meet and have children also increases. Using a Punnett square, calculate the genotypic ratio
and the sickle-cell disease phenotypic ratio of the offspring of two heterozygous parents. Please use A to
designate the normal hemoglobin allele and S to designate the sickle-cell hemoglobin allele. Be sure to include:
(4 points)




The diploid genotypes of the parents
A Punnett square showing the parental haploid gametes and the potential diploid offspring
A genotypic ratio
A phenotypic ratio of sickle-cell disease
 A statement of why expression of the sickle-cell and normal hemoglobins in a heterozygous individual
is codominant.
 A statement of why sickle-cell disease is a recessive phenotype
 A statement of why sickle-cell disease is pleiotropic.
 A statement of the probability that this couple will have a child with sickle-cell disease
 A statement of the probability that this couple will have a child with resistance to malaria
Score:
/25
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