Name _______ANSWER KEY____________________
Mrs. Geithner-Marron (Bio 200)
Date ________
Period _______
Genetics & Evolution Review Sheet Test 2011-12
Genetics
1. What is a gamete? A sex cell used for reproduction with ½ the regular # of chromosomes as an
organism’s regular body (somatic) cells
2. How many chromosomes are found in a human gamete? 23
3. How does the number of chromosomes in a human gamete compare to the number of chromosomes
in a human body (somatic) cell? Why is this important? a gamete has ½ the regular # of
chromosomes as an organism’s regular body (somatic) cells so that when fertilization occurs,
the offspring has the correct # of chromosomes (& not too many)
4. What is an allele? different forms of a gene for the same trait (ex. brown/blonde hair)
5. Compare/contrast dominant & recessive alleles.
Dominant alleles: “block” the expression of the recessive allele, can be expressed (in the
phenotype) when part of a homozygous dominant genotype or a heterozygous genotype, are
represented by a capital letter
Recessive alleles: are “blocked” by the dominant allele, can be expressed (in the phenotype)
ONLY when part of a homozygous recessive genotype, are represented by a lower-case letter
6. How many alleles for a single trait do we get from each parent? 1 from each parent (So, we have
a total of 2 alleles for each trait.)
7. What is genotype? The allele combination an organism has for a trait. Written as a
combination of 2 letters, ex. TT, Tt, tt.
8. What is phenotype? How the genotype is expressed/”seen” (physically, physiologically,
behaviorally). Usually given as an adjective (ex. purple, tall, color-blind)
9. What does it mean when an organism’s genotype is homozygous? How is this represented?
Homozygous means that the organism has 2 of the SAME alleles for a trait. This is
represented by using 2 of the same case letters, ex. TT or tt.
10. What does it mean when an organism’s genotype is heterozygous? How is this represented?
Heterozygous means that the organism has 2 of DIFFERENT alleles for a trait. This is
represented by using 1 letter of each case, ex. Tt.
Name _______ANSWER KEY____________________
Mrs. Geithner-Marron (Bio 200)
Date ________
Period _______
11. Why must an organism that shows the recessive trait be homozygous for that trait?
B/c if it had even one dominant allele, that dominant allele would “block” the recessive allele
from being expressed/”seen”
12. The trait we see (ex. flower color, hair color, etc.) is due to the __protein__________ that is
made as a result of transcription and translation.
13. In a Punnett Square, the letters along top & side represent _the alleles in each parent’s gametes
(sperm or eggs)___________.
14. In a Punnett Square, the boxes represent __the possible genotypes of the offspring resulting
from the cross__________.
15. A female has which 2 sex chromosomes? ____XX________ A male? ____ XY________
16. Which parent’s chromosomes determine the sex of the offspring? Explain your reasoning. Dad’s
(male) b/c mom always gives an X to the offspring. If dad gives an X, the offspring is a girl.
If dad gives a Y, the offspring is a boy.
17. What is codominance? When 2 alleles are equally dominant and both traits show up in the
heterozygous offspring. Represented by 2 captial letters. Ex. Roan cows have both red &
white hairs, which are codominant. The genotype of a roan cow is RW.
18. What is meant by multiple alleles? Give an example of a trait that is controlled by multiple alleles.
Even if a gene has multiple alleles, a person can only have how many of those alleles? Multiple
alleles are when there are more than 2 different genes (alleles) for a trait. Human blood
types are controlled by multiple alleles (There are 3 alleles: A, B, & o). A person can ONLY
have 2 alleles even if a gene has more than 2 versions b/c a person gets 1 allele from mom &
1 from dad. Ex. A human can have an AB genotype for blood type, but not ABo.
19. When a trait is sex-linked it is carried on only which type of chromosome (body or sex)? On a sex
chromosome (X or Y, but usually on X, b/c Y is smaller & doesn't carry many genes/alleles).
20. _____(Males/Females)_____ will have only 1 allele for traits carried on the X chromosome.
b/c a male only has 1 X chromosome... the Y doesn't carry an allele.
Name _______ANSWER KEY____________________
Mrs. Geithner-Marron (Bio 200)
Date ________
Period _______
21. When making a Punnett Square for ___sex-linked__________ traits (such as hemophilia), you
must consider the sex chromosome (X or Y) & gene it carries (shown as superscript/exponent)
together as a unit… ex. XG.
22. What does it mean that a female is a carrier for a (recessive) X-linked trait? If a female is a
carrier for an X-linked trait, she has a heterozygous genotype, ex. XGXg. She, herself, does
not have the trait/disorder b/c she has the dominant "normal" allele, but she does carry the
recessive "affected" allele that can be passed on to her offspring.
23. Sex-linked traits that are controlled by recessive alleles on the X-chromosome are more likely to
show up in _____(males/females)_____. Why? b/c a male only has 1 X chromosome... the Y
doesn't carry an allele. So, while a female can have 3 genotypes: XGXG, XGXg, XgXg (2 of
which do not cause her to be affected b/c they contain at least 1 dominant allele), a male
can only have 2 genotypes: XGY & XgY (only 1 of which does not cause him to be affected b/c
it contains the dominant allele).
24. What category (autosomal recessive, autosomal dominant, sex-linked, or chromosomal abnormality)
do the following genetic disorders fall into?
a. Cystic Fibrosis, Sickle-cell, Tay-Sachs Disease autosomal recessive (most genetic disorders)
b. Huntington’s Disease autosomal dominant
c. Hemophilia & Color Blindness seX-linked (recessive)
d. Down Syndrome (trisomy 21) & Klinefelter’s Syndrome (XXY) chromosomal abnormality
25. What is non-disjunction? What genetic disorders result from non-disjunction? non-disjunction is
when chromosomes fail to separate correctly during meiosis (1 or 2), causing too many or too
few chromosomes in the resulting gametes (sperm or eggs).
Evolution
26. What formed in the ocean before the first cells? amino acids & other simple organic molec.
27. Which gas was not part of Earth’s early atmosphere? oxygen
28. The first cells were ____heterotrophic.
29. Define evolution. theory that species have changed gradually over time (as a result of the
changes in allele frequency due to natural selection)
Name _______ANSWER KEY____________________
Mrs. Geithner-Marron (Bio 200)
Date ________
Period _______
30. What are the 4 mechanisms of evolution? Give a brief description of each.
1. migration: gene frequencies change as individuals move in or out of the population
2. genetic drift: change in gene pool of small population that takes place by CHANCE
3. mutation: random change in DNA sequence of a gene (can change amino acid sequence &
protein coded for… can change the way the trait is expressed)… not all mutations
matter in evolution, to matter they must be heritable (in gametes)
4. natural selection: organisms with variation best suited for environment tend to survive,
& reproduce (“survival of the fittest”)… more offspring will have favorable adaptation
than before. …acts on individuals, but causes evolution of a population (by changing the
allele frequencies in gene pool).
31. Describe Jean-Baptiste Lamarck’s explanation for how evolution occurs. What was his theory
called? Give an example. “Theory of Acquired Characteristics”  acquired traits are passed on
& lead to changes in species… Ex.  giraffe could acquire longer neck by reaching for leaves
on higher branches & would pass this characteristic on to their offspring
Ex. Tattoo passed
to offspring… Experimentation did not support Lamarck’s theory.
32. What are Darwin’s 4 main points related to his “Theory of Natural Selection”? Give ex of each.
1. Overproduction of offspring: more offspring are produced than generally survive to
ensure that at least some will survive long enough to reproduce & pass on genes
2. Struggle to survive (competition): more organisms than resources to go around leads to
competition (for food, water, shelter, mates, light, nutrients, etc.).
3. Variation within population: there are differences in traits in a population… Individuals
w/ variations for traits adaptive for their environment have a better chance of survival,
& thus, leave more offspring… What causes variety?  sexual reproduction, crossing
over during meiosis, arrangement of chromosomes during meiosis, mutations… Variations
can be adaptations & are NOT a response to the environment, they just happen to be
“useful” when environment changes.
4. Successful reproduction (“natural selection”): Those organisms best suited for
environment tend to survive, reproduce, & pass on genes (“survival of fittest”) leading
to more offspring that have the favorable adaptation than before.
Name _______ANSWER KEY____________________
Mrs. Geithner-Marron (Bio 200)
Date ________
Period _______
33. What are the 4 things that can cause variations amongst the individuals of a population? Give a
brief description of how each causes variation.
1. sexual reproduction: combining alleles from 2 genetically different parents (instead of
just copying DNA, like in asexual reproduction)
2. crossing over during meiosis: pieces of chromosomes are swapped during crossing over
during prophase 1 of meiosis
3. arrangement of chromosomes during meiosis: how chromosomes align during metaphase 1
or 2 of meiosis determines which chromosomes go into which gametes (& in which
combinations)
4. mutations: random change in DNA sequence of a gene (can change amino acid sequence
& protein coded for during translation) which can change way trait is expressed
34. Darwin did not have knowledge of ___genetics_______.
35. Who came up with a similar explanation for evolution as Darwin? (Alfred) Wallace
36. Compare the depth of a rock layer with it age. The lower/deeper the rock layer, the older the
rocks & the higher/shallower the rocks layer, the young the rocks (b/c layers on top were
deposited after the ones below…) (In other words, older rocks are on the bottom & younger
rocks are on the top.) This is known as the Law of Superposition.
37. What is a homologous structure? Give an example. Homologous structures are structures that are
similar in structure (and sometimes function) but with some modifications. They are evidence
of a common ancestor and of divergent evolution (in which the organisms are becoming more
different). Ex. human arm/hand, whale flipper, dog’s front leg, bat wing, bird wing,
crocodile’s front leg  all have similar bone structures & patterns (w/ some modifications)
38. What is an analogous structure? Give an example. Analogous structures have similar functions,
but not structures due to similar environment/use. Organisms do NOT have common ancestor,
but have structures that are becoming more similar (convergent evolution) due to similar
usage. Ex. insect wing & bird wing  both are used to fly, but insect wings don’t have bones
while bird wings do
Name _______ANSWER KEY____________________
Mrs. Geithner-Marron (Bio 200)
Date ________
Period _______
39. What is a vestigial structure? Give an example. Vestigial structures are structures with
decreased size or function. They often have no apparent use in the present organism.
Vestigial structures are evidence that an organism has changed. Ex. hip bones in whales
(evidence of the fact that whales had ancestors that had legs & walked) & appendix in humans
(apparently used when our diets were more plant-based & less animal-based).
40. How do embryos, provide evidence for evolution? When looking at embryos of organisms… the
early stages are very similar, which is evidence that they inherited same basic body plan from
a common ancestor. In the later stages there is more distinction… the greater the # of
similar stages, the more closely related the organisms are (& the more recently they split
from their common ancestor).
41. How does biochemistry (DNA, amino acids, proteins, etc.) provide evidence for evolution? Similar
organic compounds are coded for by similar DNA (ex. proteins). DNA is the most reliable
form of evidence. If 2 very different species share (large amounts of the same) DNA it is
evidence of common ancestry. The higher %, more closely related (ex. human & chimpanzees
98% similar; humans & other mammals 80% similar)
42. Are adaptations a response to the environment (a choice) or do they just happen to be “useful”
when the environment changes? Explain your reasoning. Adaptations are NOT a response to
environment! They just happen to be “useful” when environment changes. Certain features are
not developed “in order to” adapt to change in env…. Variation already exists in population &
certain variations become useful when env changes… The organisms w/ the best-suited
variations survive & produce offspring while others die before they can reproduce… in this way
a population/species becomes adapted to its environment…
43. ___Evidence___________ for evolution includes the fossil record, comparative anatomy,
comparative embryology, comparative biochemistry, and direct observation (such as antibioticresistant bacteria and pesticide-resistant insects).