Download Genetics Test Review KEY 15

Name: ___________________________
Due: ______
Genetics Test Review
1. __Genetics __ is the study of heredity.
2. Who is considered to be the Father of Genetics? Mendel
3. What is the difference between a gene and an allele?
A gene is a section of a chromosome that codes for a trait (more specifically a polypeptide); an allele is the form a
gene may take. For example, if the gene is for eye color, the alleles may be brown, black, blue, gray, green, blue, etc.
4. Use the alleles T and t for height to fill out the table
Genotype
Phenotype
Homozygous Dominant
TT
Tall
Homozygous Recessive
Tt
Tall
Heterozygous
tt
Short
5. What is the difference between homozygous and heterozygous? Give an example
Homozygous is when both alleles are alike for a trait are either both dominant (AA) or both recessive (aa).
Heterozygous is when the alleles for a trait are different – one dominant and one recessive (Aa)
6. What is the difference between genotype and phenotype? Give an example.
Genotype – genetic make-up of an organism – composition of alleles (letters). Ex. Tt.
Phenotype – physical appearance of an individual  a result of a genotype. Ex. Tall or short plant
7. What is the difference between a dominant versus a recessive trait? Give an example
When a dominant allele shows up in the phenotype of the organism, it masks the recessive allele. Having a widow’s peak is
dominant to a straight hairline. Conventionally, dominant traits are indicated by a capital letter, so in this case W = widow’s peak
and w = straight hairline.
8. __Incomplete dominance__ - this type of inheritance shows a blending effect. In other words, the dominant allele
does not completely cover the recessive allele. Give an example. Cross between red and white flowers  PINK
9. Co-Dominance – both alleles of a trait are expressed (show) in a heterozygous individual. Give an example.
Red and White  Roan
10. _Sex- linked inheritance__ - type of inheritance where the allele is found on the sex chromosomes; usually the X
chromosome. Give an example. Hemophilia, colorblindness
11. What are the genotypic and phenotypic ratios and percentages for the following genetic combinations?
SHOW ALL WORK USING alleles R and r for monohybrid crosses and R, r, S, s for dihybrid crosses.
a. Heterozygous x heterozygous – Genotypic: 1:2:1;
Phenotypic: 3:1
What percentage of their children will be homozygous dominant? 25%
b. Heterozygous x homozygous dominant – Genotypic: 1:1 Phenotypic: 1:1
What percentage of their children will be heterozygous? 50%
c. Dihybrid heterozygous for both traits x heterozygous for both traits – Phenotypic: 9:3:3:1
12. If a genetic trait displays epistasis, what does that mean? When one gene controls the outcome of the other
13. Example of epistasis.
If P = purple flower petals and p = whit flower petals and for a second trait C = color on and c = color off, then what
would be the phenotypes for the following possible genotypes?
CCPP = purple CCPp = purple
CcPP = purple
CcPp = purple
CCpp = white
Ccpp = white
ccPP = white
ccPp = white
ccpp = white
14. XX = female; XY = male; who determines the sex of a child? father
15. Hemophilia is a sex-linked recessive trait. What is the genotype for:
a. A female with normal blood clotting factor - XHXH
b. A female whose blood clots normally, but who is a carrier for the trait - XHXh
c. A female hemophiliac - XhXh
d. A male with normal blood clotting factor - XHY
e. A male hemophiliac - XhY
16. What are the genotypes and phenotypes for blood typing? What kind of trait is blood typing?
Blood typing is a multiple allele trait; Types A and B are co-dominant to each other and are both dominant to Type O. Type O is
the recessive.
Phenotype
Type A
Type B
Type AB
Type O
Genotype
AA, AO
BB, BO
AB
OO
Another way to write genotype
IAIA or IAi
IBIB or IBi
IAIB
ii
17. How can a parent, with A blood and a parent with B blood have children with O type blood? Support
algebraically or with a Punnett Square.
If both parents are heterozygous, then there is a 25% chance that they will have a child with Type O
blood. Parents = (AO x BO)
18. Which blood type is the universal recipient? Donor? Why?
Type AB is the universal recipient because these cells have both antigens on their surfaces and
would not recognize anything else as incompatible or the enemy.
Type O is the universal donor because these cells don’t have either antigen on their surfaces;
therefore, they will recognize anything as foreign and will start the immune response.
19. What type of trait does this pedigree show, dominant or recessive? We
will look at these after Christmas
How do you know?
Who shows the trait?
Are any of the members of the family carriers?
20. Total Ridge Count is a polygenic trait. (on fingerprints)
AABBCCDD represents a maximum ridge count and aabbccdd represents a minimum ridge count with a baseline of
60 for males and 30 for females. Each additional dominant allele adds 10 ridges to the TRC.
Genotype
Phenotype Male
Phenotype Female
aabbccdd
aaBBccDd
AabbCCDd
AAbbCCdd
60 (no dominant)
=60+ 3x10= 90
=60+ 4x10= 100
=60+ 4x10= 100
30 (no dominant)
=30+3x10= 60
=30+ 4x10= 70
=30+ 4x10= 70
AABBCCDD
=60+ 8x10= 140
=30+ 8x10= 110
Genetic Crosses
Solve the following monohybrid crosses. MUST SHOW YOUR WORK!
21. If out of 100 offspring of corn, 74 have round kernels and 26 have wrinkled, what are the probably genotypes and
phenotypes of the parents? Assume that round kernels are dominant. Parents are probably Rr and round.
R
r
R
RR
Rr
r
Rr
rr
22. Mating two pink flowers results in the following ratios: 25% white, 25% red and 50% pink. What were the parental
genotypes and what pattern of inheritance is this? Both were heterozygotes
23. Mating a roan (red +white haired) bull with a white cow produces 50% white and 50% roan calves. Explain what
patterns of inheritance this is and how you know. This is codominance, because both phenotypes appear in the
heterozygote
24. If Cindy and Bobby both have type A blood, can they have kids that have type O blood? Explain.
Yes, they can both be Heterozygous. They will have a 25% chance of type O blood children.
IA
i
IA
IAIA
IAi
i
IA i
ii
25. In fruit flies, the gene for white eyes is sex-linked recessive. (R) is red and (r) is white. Cross a white-eyed female with
a normal red-eyed male.
a. What percent of the males will have red eyes? White eyes? 100% have white eyes
b. What percent of the females will have red eyes? White eyes? 100% have red eyes
c. What total percent of the offspring will be white-eyed? 50%
d. What percent of the offspring will be carriers of the white eye trait? 50%
XR
y
Xr
XR Xr
Xry
Xr
XR Xr
Xry
Solve the following dihybrid cross. MUST SHOW YOUR WORK!
26. In summer squash, white fruit color (W) is dominant over yellow fruit color (w) and disk-shaped fruit (D) is dominant
over sphere-shaped fruit (d). If a squash plant homozygous for white, disk-shaped fruit is crossed with a homozygous
for yellow, sphere-shaped fruit, what is the chance of producing a yellow disked fruited plant? 0% chance!
WD
WD
WD
WD
wd
WwDd
WwDd
WwDd
WwDd
wd
WwDd
WwDd
WwDd
WwDd
wd
WwDd
WwDd
WwDd
WwDd
wd
WwDd
WwDd
WwDd
WwDd