Download Honors Biology - Genetics Study Guide

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
(blue eyes - bb). Dominant alleles are always expressed when present (brown eyes - BB or 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 (heterozygous). (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. allele vs. gene
Gene is enough DNA to code for 1 protein (or 1 trait). Alleles are the alternative forms of a gene. For
example, you would have a gene that codes for eye color. You could then have a brown allele, blue allele,
etc.
h. law of segregation vs. law of independent assortment
Segregate means to separate. Law of segregation says that homologous chromosomes are separated
during anaphase I of meiosis (or in other words, a gamete loses half its DNA to become haploid). This is
why when we draw a Punnett square, if someone is heterozygous (Aa) they can give either the dominant
or recessive allele.
Law of independent assortment says that homologous chromosome pairs line up independently of one
another during metaphase I; therefore, traits such as hair color and eye color are not linked and can thus
be inherited independently of each other. (You can have blonde hair and brown eyes, blue eyes, or
whatever)
i. polygenic inheritance vs. multiple alleles
Polygenic says that there are many genes affecting one trait. These phenotypes will be seen on a
continuum. Ex. hair and skin color
Multiple alleles means that there are several different alleles at the same locus (gene). Ex. blood type
j. homologous chromosomes
chromosome of same size, shape, and same genes at same locus (1 from mom and 1 from dad)
k. carrier
Heterozygous for recessive trait (do not phenotypically show it but can have offspring who do)
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?
R
R
r Rr
Rr
r Rr
Rr
Genotype: Rr, Phenotype: Pink
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)?
R
R RR
r Rr
r
Rr
rr
RR = red so 25%
6. What would the phenotypic ratios of the offspring be if you were to cross DdEe x DdEe?
D
d
D DD
Dd
d Dd
dd
E
E EE
e Ee
e
Ee
ee
Phenotypic ratio for dihybrid is as follows: D,D: D,r: r,D: r,r
9 :3 :3 : 1
7. In the dihybrid cross AaBb x AaBb, how many different phenotypes are possible in the offspring?
Use the Punnett squares from #6, there are 4 possible phenotypes.
8. In the dihybrid cross AaBb x AABB, what are the possible genotypes for the offspring?
A
a
A AA
Aa
A AA
Aa
B
B BB
B BB
b
Bb
Bb
Possible Genotypes: AABB, AABb, AaBB, AaBb
9. In a monohybrid cross, how many phenotypes are possible if the parents are both true breeds? What if they
are both heterozygous?
E
E EE
e Ee
e
Ee
ee
E
e Ee
e Ee
E
Ee
Ee
First Punnett sq: heterozygous: 2 phenotypes (3:1)
2nd Punnett sq: true breeds: 1 phenotype (4:0)
10. What fraction of the offspring would have the genotype aabbcc if we were to cross AaBbCc x AaBbCc?
A
A AA
a Aa
a
Aa
aa
Same Punnett sq. for all 3.
¼ for each are homozygous recessive so ¼ X ¼ X ¼ = 1/64
11. 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?
Xc
XC XCXc
Y XcY
Xc
XCXc
XcY
Genotypes: XCXc or XcY
Phenotypes: Normal (Carrier) Female, colorblind male
12. 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?
XC
Xc
Xc XCXc
XcXc
Y XCY
XcY
Shouldn’t have asked for genotype ratio here. Won’t really see that much w/ sex-linked.
Phenotype: 2:2
13. If a female's father was colorblind, and only one of her two sons is colorblind, what is her genotype?
X
Xc XXc
Y XY
X
XXc
XY
If her dad was colorblind, then she has to at least be a carrier (depending on what mom has) because she
has 2 X alleles and one of them came from her father (who only had a colorblind X to give). For her sons
to be colorblind, they would have to get the allele from her (because for them to be boys they would
receive the Y from the dad). So she is at least a carrier.
14. 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.
15. If a trait for free earlobes is autosomal recessive, and a female has free earlobes, what is her genotype?
Autosomal means it is not sex linked. To show a recessive trait, an individual must have no dominant
alleles.
ee
16. Can a male be a carrier of an autosomal recessive disorder?
yes, it is not linked to an X chromosome. Ee could be male or female
17. Is it possible for a male or female to be a carrier of an autosomal dominant disorder?
No, homozygous dominant people and heterozygous individuals show the same phenotype.
18. What are the genotypes for the following blood types?
Blood
Type
A
Genotype
IAIA, IAi
B
IBIB, IBi
AB
IAIB
O
ii
19. Could a child with type O blood have a father with type AB blood?
No. They would have to receive 1 allele for blood type from each parent (so have to get A or B from dad).
20. 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?
IA
IB IAIB
i IAi
i
IBi
ii
All blood types (AB, A, B, O) are possible if both parents are heterozygous.
21. 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
22. Why can't people with type O blood receive blood from anyone but other with type O?
Because type O blood has antibody A and antibody B, which will cause any other blood type to clot.
23. What are the following represented by in a pedigree chart:
Normal Female
Carrier Female
(Sometimes you will see a half filled in circle for carrier females. Other times it
will just be shown as a white circle because phenotypically the female is normal)
Female with disorder
Normal Male
Male with disorder
24. A cross was done between 2 flowers exhibiting incomplete dominance and all of the offspring were pink.
a. What are the genotypes of the parents?
b. What are the phenotypes of the parents?
c. Draw a Punnett square showing this crossing.
a. RR x rr
b. Red x White
c.
R
r Rr
r Rr
R
Rr
Rr
Use the pedigree below to answer questions 25-28
25. Label the generation and individual numbers for the pedigree. Generations are labeled on the left side
in roman numerals (so I for the top line, II for the second, and III for the 3rd). Individual people are
numbered from left to right (Ex. 1, 2, 3..). It is also possible to restart the number for each generation
(Ex. I – 1, 2; II – 1, 2, 3, 4, 5, 6)
26. Write the genotype for each individual under their symbol. If there is not enough information to
determine the phenotype of an individual then put a ? for the 2nd allele.
We know that this is a sex-linked trait because only the boys are showing it. That means that boys
must only get 1 X to have the disorder.
1. XCY
2. XCXc (We know she is a carrier because her son has it. Remember that boys receive a Y from their
dad so the only X they will have is from their mother. If he has it, it had to come from her.
3. XCY
4. XCXc (same reasoning for person 2)
5. XCX? (not enough information to tell – mother is a carrier but she could’ve gotten the normal X or
the disorder X)
6. XcY
7. XCX?
8. XcY
9. XCX?
10. XCXc (We know that she is a carrier because her dad has the trait. She has to get 2 X’s - 1 from
each parent. Since her dad only had 1 X to give, she must be a carrier)
11. XCY
27. Individual 1 in generation III mates with a female who is a carrier for colorblindness.
a. Draw this female into the pedigree.
b. Create a Punnett square predicting the offspring of these 2 individuals.
XC
Xc
Xc XCXc
XcXc
Y XCY
XcY
c. What percentage of their offspring would be expected to be colorblind?
50%
28. Individual 3 in generation III mates with a normal male.
a. Draw this male into the pedigree.
b. Create a Punnett square predicting the offspring of these 2 individuals.
XC
Xc
XC XCXC
XCXc
Y XCY
XcY
c. What percentage of their offspring would be expected to be colorblind?
25%
29. What happens in metaphase of meiosis that explains the laws of segregation and independent
assortment?
Law of segregation: Homologous chromosomes separate during anaphase I.
Independent assortment: Chromosomes line up independently of each other in metaphase I.