Download Name : Date: ______ Block: _____ Genetics and Evolutionary

Name : _______________________
Date: ____________ Block: _____
Genetics and Evolutionary Theory
Read pages 299-302 and fill in the blanks. Also highlight any bolded words in the text.
1.
Darwin did not know about __genetics___. However, genetics and __evolutionary_ theory are
inseparable. Today, we _define_ fitness, adaptation, _species_, and the process of evolutionary
change in _genetic _ terms.
Genes Units of Variation
2. Genes, the carriers of _inheritable__ characteristics, are also the __source_ of the _random__
variation upon which _natural selection__ operates. _Mutations_ cause some variation. Much
additional variation arises during _meiosis_ as the parent’s _chromosomes_ are copied, shuffled
like a deck of __playing_ cards, and dealt out to the _gemetes_.
3. It is _Important__ to remember that __genetic__ variation does not occur because an
_organism__ needs or _wants_ to _evolve_. Sometimes _genetic _ variation occurs; sometimes it
_doesn’t___. When variations do _occur__, natural selection then goes to work, selecting the
__successful __ ones.
Raw Material for Natural Selection
4. In the _evolutionary__ struggle for _existence_, entire organisms, not __individual_ genes, either
survive and __reproduce_ or do not. Therefore, _natural selection_ can operate only on the
phenotypic ___variation__ among __individuals_. Phenotype refers to all the _physical_and
_behavioral___ characteristics produced by the __interaction_ of genotype and environment.
(Character traits that you can see).
5. You can _sample_ the phenotypic variation by _measuring_ the height of all the students in your
class. Using _mathematics__ you can calculate an average __height_ for this group. Many
_students___ will be just a little taller or ___shorter__ than average. However, a few very _tall_
or very __short_ individuals may be in your class. If you graph the number of _individuals__ of
each height you will get a _curve_ like this:
6.
This _phenotypic__ variation is produced by a _combination_ of genetic instructions and
_environmental_ influences, such as _diet___ and exercise. If your _classmates__ are not
malnourished, most(though not all) of the _variation__ in height you __observe_ can be said to
result from differences in _genotype__. Of course you can also _observe__ many other kinds of
_phenotypic_ variation among your classmates. For example, variations in skin, _hair_ and eye
color, and variations in the _shapes_ of noses , the curves of lips and the _amount_ of body hair.
7. In _nature__, organisms show as__many__ variations as humans, although most humans are not
_aware_ of this. For example to the casual _observer_ , one _zebra___ looks much like any other
Name : _______________________
Date: ____________ Block: _____
__zebra_. But when _researchers_ study the characteristics of many __individuals__ of a species
they find the same sort of distribution for each _characteristic_ that you saw in human _height_.
It is this sort of variation in organisms that provides the raw material for __natural_ selection.
Evolution as Genetic Change
8.
In order to _describe__ the evolution of plants and _animals_, modern evolutionary biologists
study _groups_ of organisms called populations. A population is a collection of _individuals__ of
the same species in a given _area_ whose members can __breed__ with one __another_. For
example all the fishes of a certain _species_ in a single pond could be considered one
_population__. Individuals in _another__ separate pond would belong to a _different__
population, even if that pond was close by.
9. Because all _members_ of a population can __interbreed_, they and their offspring share a
_common__ group of genes, called a gene pool. Each gene pool _contains__ a number of allelesor forms of a certain _gene_ at a __given_ point on a chromosome-for each __inheritable__ trait
including _alleles___ for recessive traits. The number of __times_ an allele occurs in a gene pool
compared with the __number__ of times other alleles for the __same_ gene occur is called the
relative _frequency__ of the allele.
10. _Sexual__ reproduction alone does not _change__ the relative frequency of __allele_ in a
population. To understand why, you can compare the _combination___ of alleles produced by
sexual reproduction to the different _cards__ you get when you shuffle and deal a _deck_ of
playing cards. Shuffling and __reshuffling_ produce an enormous variety of different _hands_.
But shuffling _alone_ will not change the relative _frequency__ of aces, kings, fours or _jokers__
in the deck.
11. With this in _mind_, we can view evolution in another way. _Evolutionary__ change involves a
change in the relative _frequencies_ of alleles in the gene pool of a _population__. And as you
can see in the graph below, when the __relative__ frequencies of alleles in a _population_ change,
the curves that describe the __distribution_ of traits controlled by those alleles also _change__.