Name: ______________________________
STUDY GUIDE FOR HEREDITY TEST ON FRIDAY, JANUARY 23
Define the following terms:
Core: _______
1. Trait: a physical or behavioral characteristic that describes an organism (Ex: height, eye color)
2. Genetics: the study of genes, heredity, and genetic variation.
3. Genes: a section of DNA that determines a trait.
4. Allele: the different forms of a gene.
5. Homozygous: having the same allele for a particular gene (NN or nn).
6. Heterozygous: possessing two different forms of a gene, one inherited from each parent (Nn).
7. Sex-linked trait: traits that are carried on sex chromosomes (X or Y). Example: colorblindness is a X-linked trait.
8. Autosomal trait: traits that are carried on non-sex chromosome.
9. Mutation: a random change in an organism’s DNA.
10. Artificial selection: the process by which humans select certain desirable traits in other organisms; also called
“selective breeding”
11. Natural selection: the process by which conditions in the environment cause certain beneficial “traits” to be
passed to the next generation. This results in changes in inherited characteristics of a population.
12. Survival of the fittest: Some individuals with certain traits are better suited for the environment and will survive to
reproduce the next generation.
Short answer questions:
13. What is the Theory of Evolution by Natural Selection” proposed by Charles Darwin? Be sure to explain the
difference between microevolution and macroevolution.
The Theory of Evolution is the process by which different kinds of living organisms are thought to have developed
and diversified from earlier forms during the history of the earth.
Microevolution (natural selection; changes within species)
Macroevolution (one species changes to another species)
14. Explain how you know that fathers DO NOT pass on X-linked recessive disorders to any of their sons. Show your
work with a Punnett Square.
Fathers do not pass on any X-linked disorders (dominant or recessive) to their sons, because fathers will only pass on the
Y chromosome to their sons. The chromosomes that code for gender in a male are XY and for female it is XX. Males
receive the X chromosome from their mother and the Y chromosome from their father. Females receive an X
chromosome from their mother and an X chromosome from their father. A father who has an affected X chromosome
will pass the trait on to their daughters, but never to their sons. The Punnett Square below shows a father who has an
X-linked recessive trait on his X chromosome, designated as X’. His genotype is X’Y. He is married to an woman who is
unaffected by the X-linked recessive trait and her genotype is XX.
There is a 50% chance that they will have a daughter. Every daughter from this combination
will be a carrier of the X-linked recessive disorder (X’X). There is a 50% chance they will have
a son. Every son will not have the X-linked recessive disorder, because they would receive an
unaffected X chromosome from their mother and the Y from their father.
15. Removed from study guide.
Punnett Squares Practice Questions - What would you expect the phenotypes and genotypes of this cross to be?
16. A heterozygous black rabbit (Bb) with a homozygous recessive white rabbit (bb).
Genotypes: 50% Bb; 50% bb
Phenotypes: 50% black; 50% white
17. A homozygous red flower (RR) with a homozygous white flower (rr).
Genotypes: 100% Rr
Phenotypes: 100% red flowers
18. A blue-eyed father and a blue-eyed mother.
**Blue eyes are recessive (bb)  bb x bb
Genotypes: 100% bb
Phenotypes: 100% blue eyes
19. A heterozygous straight-haired dog with a homozygous curly-haired dog.
With a Hh genotypes (heterozygous), the phenotype was straight hair. That indicates that the dominant
allele (H) codes for having straight hair. Therefore the homozygous curly genotype must be recessive
(hh), because that is the only way it can be expressed. The cross is therefore Hh x hh.
Genotypes of the offspring: 50% Hh; 50% hh
Phenotypes: 50% straight hair; 50% curly
20. A color-blind father (XnY) and a normal-seeing carrier mother (XNXn). Colorblindness is an X-linked recessive trait.
Genotypes:
25% XNXn
25% XnXn
25% XNY
25% XnY
Phenotypes:
Female who is a carrier for colorblindness
Female who is colorblind
Male who has normal vision
Male who is colorblind
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21. A mother without Hemophilia (XNXN) and a father with hemophilia (XnY). Hemophilia is also X-linked recessive.
Genotypes:
50% XNXn
50% XNY
Phenotypes:
Female who is a carrier for Hemophilia
Male who has normal vision
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22. In Gregor Mendel’s first experiment with pea plants, he bred purebred tall plants with purebred short plants.
Purebred tall = TT
Purebred short = tt
Genotypes = 100% Tt
Phenotypes = 100% tall
23. In Gregor Mendel’s second experiment with pea plants, he bred two of the offspring tall plants produced from his
first experiment.
Second experiment = Tt x Tt
Genotypes = 25% TT; 25% tt; 50%Tt
Phenotypes = 75% Tall & 25% Short
Pedigree Chart Practice Questions:
24. What is the symbol for the following in a pedigree chart?
a) A male who expresses the trait
d) A male who does not express the trait
b) A female who expresses the trait
e) A female who does not express the trait
c) A marriage
f) Four siblings (two twin boys, 1 boy, & 1 girl)
25. Fill in the genotypes for the following AUTOSOMAL DOMINANT trait (use H &h for the alleles).
26. Fill in the genotypes for the following AUTOSOMAL RECESSIVE trait (use H &h for the alleles).
27. What is the Theory of Evolution by Natural Selection proposed by Charles Darwin? (See answer above). Describe
the 2 observations that contributed to this idea and the 2 assumptions that are necessary for this idea.
-Observed that a population can outgrow its resources which would lead to competition for existence among offspring. This is called
the “struggle for existence.” Members of each species have to compete for food, shelter, and other life necessities. Another
observation is that those that have better traits for that environment will survive to reproduce the next generation. This is called
“survival of the fittest” and it is observable in nature. This is also described as “natural selection” because in this way the
environment is “selecting” for the better traits. This is also observable in nature. One assumption that Darwin made was that the
earth is very old. Not all scientists agree on this point and the age of the earth is a controversial issue. The idea is that billions and
billions of years would be necessary for these random changed in genetic information (mutations) working together with natural
selection would be necessary for macroevolution to occur (species changing to different species). This is linked to the second
assumption that small changes over time can eventually lead to larger changes over a long enough period of time (one species
changes into something different = “evolution”). This stems from the evolutionary idea that all living organisms came from an
original common ancestor (common descent) and that all organisms descended over time with small changes (descent with
modification).