Download Name - Animo Venice Biology

Name __________________________________________________ Date ________________ Period ______
Genes and Variation
Remember…
• In order for natural selection to occur, there MUST be variation.
•
Variation in the genes then creates variations in the phenotype.
•
Natural selection then “chooses” those phenotypes that are most favorable.
Genetic variation is studied in Populations
•
A population is ______________________________________________________________________
•
Because members of the population interbreed, they share a common group of genes called a gene pool.
•
A gene pool consists of _______________________________
__________________________________________________
__________________________________________________
•
The relative frequency of an allele is ___________________
__________________________________________________
__________________________________________________,
compared to the number of times other alleles for the same
gene occur.
What are the main sources of genetic variation in a population?
I. Mutations
•
A mutation is _____________________________________
_________________________ (insertion, deletion, point shift, etc.)
– Mutations can be caused by replication errors, radiation,
and/or chemicals in the environment.
II. Gene Shuffling
•
Gene shuffling is _______________________________
______________________________________________
– Occurs during gamete formation (meiosis) when chromosomes
cross over, as well as when they are randomly pulled apart
during anaphase I and II.
Single-Gene Traits and Polygenic Traits.
•
A single-gene trait is __________________________________________________________________
____________________________________________________________________________________
•
For example, widow’s peak in humans.
– The allele for widow’s peak (W) is dominant over the allele for no widow’s peak (w).
•
Many traits in humans are controlled by
_______________________________________, and are therefore
called polygenic (many-genes).
•
A polygenic trait can have ___________________________
_________________________________________________
– For example, height. People are not either tall or short. They
can be tall, short, and everything in between.
Reflection
1. What is a gene pool?
2. If the relative frequency of one allele decreases, what would happen to the relative frequency of the
other allele? Explain.
3. What are the sources of heritable variation?
4. Choose one of the above sources and explain how it can lead to variation.
5. Why do you think variation is important in a population?
How Does Natural Selection Work on Polygenic Traits?
• Class activity: Student Height
1. Directions: Using meter sticks, record the height of each student at your table to the nearest inch. Record
the measurements in your data table.
2. When you are done, have a representative from your group come up to the front and record your numbers
in the data table on the board.
3. Make sure to record each groups’ measurements in your data table, as they are written on the board.
Table #
Student Heights
1
2
3
4
5
< 4’11” 4’11” 5’0”
5’1”
5’2”
5’3” 5’4”
5’5”
5’6”
5’7” 5’8”
5’9”
5’10” 5’11”
6’0”
>6’0”
Analysis
1. Where did the majority of the students’ heights fall?
2. What do you think the general shape of your graph, indicates about height in humans?
3. What type of selection does your graph show? How doe you know?
Types of Selection
• Natural selection can affect the distributions of phenotypes in any of three ways: ___________________
__________________, ________________________________, ________________________________
I. Directional Selection
•
Directional Selection – ________________________________________________________________
____________________________________________________________________________________
For Example: Really tall people are
more fit than average or really short
people. Those that are very tall are
then selected for, all others are
selected against.
II. Stabilizing Selection
•
Stabilizing Selection – ________________________________________________________________
____________________________________________________________________________________
For Example: Average height people
are more fit than really short or really
tall people. Those that are average
are then selected for, all others are
selected against.
III. Disruptive Selection
•
Disruptive Selection – ________________________________________________________________
____________________________________________________________________________________
For Example: Very tall and very short
people are more fit than average height
people. Those that are very tall or very
short are then selected for, all others
are selected against.