Honors Biology - Genetics Study Guide KEY
Name:_______________________
1. Explain the difference between the following & provide an example of each:
a. genotype & phenotype
Genotype refers to the genetic makeup (the letters - GG,Gg,gg) while phenotype refers to how the genetic
content is expressed (the looks - green or yellow).
b. homozygous & heterozygous
Homozygous genotype has either both the dominant alleles, or both the recessive alleles (RR, rr) while
heterozygous genotype has one of each (Rr).
c. recessive & dominant
Recessive traits are only expressed if both alleles are recessive and may often "skip" a generation
(brown eyes - BB or Bb). Dominant alleles are always expressed when present (blue eyes - bb).
d. true breed & hybrid
A true breed will always produce the same offspring and are of the homozygous form (HH, hh). The parent
generation is a true breed. A hybrid is a result of a cross. (A test cross is a method used to verify that a trait is
true breeding.
e. autosome & sex chromosome
Autosomal chromosomes are any chromosomes unrelated to sex determination (not sex linked), and sex
chromosomes are those that do determine the sex of an organism (XX, XY).
f. incomplete dominance & codominance
Incomplete dominance is when a dominant allele can not fully dominate the other resulting in a sort of blending
(chestnut horse HH, white horse hh, palomino horse Hh). Codominance is when both alleles are dominant and
both are expressed equally (red bull RR, white cow rr, roan cow Rr).
g. carrier & x-linked traits (do not need to differentiate)
A carrier is an organism that has a heterozygous genotype, the dominant allele that is expressed gives a
"normal" phenotype while they still carry the recessive allele which is the "disorder".
X-linked traits are those that are linked to the X chromosome.
Example - colorblindness.
XBXB - normal female
XBXb - carrier female
XbXb - colorblind female
XBY - normal male
XbY - colorblind male
(males can not be carriers of sex linked traits!)
2. What type of cross always results in all heterozygous offspring?
A cross between true breeds (or the P generation). FF x ff
3. What type of cross results in a 3:1 phenotypic ratio?
A cross between two heterozygous genotypes (the F1 generation). Ff x Ff
4. If you cross a red flower with a white flower, what will be the offspring's genotype and phenotype if the gene
exhibits incomplete dominance?
5. If you were to cross two roan cattle, what would be the chances of the offspring having a red phenotype
(assuming the gene exhibits codominance)?
6. What would the genotypic and phenotypic ratios of the offspring be if you were to cross DdEe x DdEe?
7. The recessive genotype (dd) results in deafness. Predict what the parents' genotype would be if the offspring's
genotype is dd (assume that the parents are both phenotypically normal)?
8. In the dihybrid cross AaBb x AaBb, how many different phenotypes are possible in the offspring?
9. In the dihybrid cross AaBb x AABB, what are the possible genotypes for the offspring?
10. In a monohybrid cross, how many phenotypes are possible if the parents are both true breeds? What if they
are both heterozygous?
11. What fraction of the offspring would have the genotype aabbcc if we were to cross AaBbCc x AaBbCc?
12. If a female that is colorblind (a sex linked trait) and is crossed with a normal male, what genotypes and
phenotypes would be possible in the offspring?
13. If a female is a carrier of the colorblind recessive allele, and the male is colorblind, what would the
genotypic and phenotypic ratios of the offspring be?
14. If a female's father was colorblind, and only one of her two sons is colorblind, what is her genotype?
15. Why are sex linked traits expressed more in males? Why can't males be carriers if a sex linked trait?
Because females have the possibility to be carriers, while males can only have the trait or not. Males can not be
carriers because they only have 1 X chromosome.
16. What does the above question illustrate about how sex-linked traits are passed from generation to
generation?
They are passed from father to daughter, and mother to son.
17. If a trait for free earlobes is autosomal recessive, and a female has free earlobes, what is her genotype?
ee
18. Can a male be a carrier of an autosomal recessive disorder?
yes, it is not linked to an X chromosome. Ee
19. What are the genotypes for the following blood types?
Blood
Type
A
Genotype
IAIA, IAi
B
IBIB, IBi
AB
IAIB
O
ii
20. What blood type could a type O child's parents NOT be?
AB
21. Could a child with type O blood have a father with type AB blood?
No
22. If a woman with type A blood had a child with a man that had type B blood, what are all the possible blood
types that the child could have?
23. What types of blood can the following individuals accept in a blood transfusion?
Blood
Types:
Types they may receive:
A
A, O
B
B, O
AB
A, B, AB, O
O
O
24. Why can't people with type O blood receive blood from anyone but other with type O?
Because type O blood has anti A and anti B, which will cause any other blood type to clot.
25. What are the following represented by in a pedigree chart:
Normal Female
Carrier Female
Female with disorder
Normal Male
Male with disorder
26. How are generations and individuals numbered on a pedigree table?
27. Fill in the below pedigree with the generation number, individual number, genotypes. Then provide the
possible phenotypes if individual 6 produces offspring with a normal male.
Autosomal recessive allele = r
Autosomal dominant allele = R
28. What is the probability that an offspring with the genotype
AaBbCcDDEd is produced by the following cross:
AaBbCCDdee x AAbbCcDDEe?