Science 10
Name:
Date:
________
Block:
REVIEW SHEET
Terms & Definitions:
1. Different forms of a specific gene
alleles
2. The passing of traits from parents to offspring
heredity
3. The crossing of two individuals with two different alleles
hybridization
4. In a pair of alleles, the one that is “stronger”
dominant
5. In a pair of alleles, the one that is “masked” by the stronger one
recessive
6. A combination of alleles (e.g. BB, Bb, bb)
genotype
7. The outward (physical) appearance of the organism
phenotype
8. An organism that is homozygous dominant for an allele e.g. BB (2 of the dominant allele)
9. An organism that is homozygous recessive for an allele e.g. bb (2 of the recessive allele)
10. The “father of genetics” (Austrian monk)
Gregor Mendel
11. A table used to predict the chance of genotype occurring
Punnett square
Question:
1. Explain at least three reasons why pea plants were used in the original heredity experiments.
1.
2.
3.
4.
5.
Easy to grow
Short life spans
Lots of traits with only 2 forms
Easy to grow and contain
Individual peas could produce both male and female gametes (self-fertilization)
Use A Punnett Square To Answer The Following Questions!
2. In humans, double-jointedness (D) is dominant to normal joints (d). Cross a heterozygous,
double-jointed female to a male with normal joints. What ratio of the offspring will be double
jointed?
Punnett Square
d
d
D d
Dd dd
Dd dd
Ratio of double jointed offspring
50% Dd (double jointed)
3. In mice, black coat colour (B) is dominant over white (b). Cross a homozygous dominant
mouse with a homozygous recessive mouse.
a) What are the genotypic and phenotypic ratios of the F1 generation?
Punnett Square
b
b
B B
Bb Bb
Bb Bb
Genotypic ratio
100% Bb
Phenotypic ratio
100% black
b) What are the genotypic and phenotypic ratios of the F2 generation?
Punnett Square
B
b
B
b
BB Bb
Bb bb
Genotypic ratio
25% BB
50% Bb
25% bb
Phenotypic ratio
75% black
25% white
(3:1 ratio)
4. Incomplete dominance: Red coat colour (R) is incompletely dominant over white coat colour
(W) in cattle; the hybrid (RW) is roan coloured.
a) If you cross a homozygous red female cow with a homozygous white bull, what are the
genotypic and phenotypic ratios of the offspring?
Punnett Square
R
R
W RW RW
W RW RW
Genotypic ratio
100% RW
Phenotypic ratio
100% roan
b) If you cross a roan bull with a white cow, what is the probability of getting roan offspring?
Punnett Square
W
W
R RW RW
W WW WW
Probability of a roan offspring
50% RW
(roan offspring)
5. Multiple alleles: ABO blood types. If a man with the blood type AB produced children with a
woman of blood type A (IAi), what are the genotypic and phenotypic ratios of the offspring?
Punnett Square
IA
IB
IA
i
A
A
A
I I I i
IAIB IBi
Genotypic ratio
25% IAIA
25% IAIB
25% IAi
25% IBi
Phenotypic ratio
50% blood type A
25% blood type AB
25% blood type B
6. Sex linkage: Coat colour in cats is sex-linked. Black (B) is dominant to ginger (b). A hybrid
(Bb) will produce an individual with a tortoiseshell coat colour
a) Cross a homozygous black female cat to a ginger male cat and write the genotypic and
phenotypic ratio of their offspring.
Punnett Square
Xb
Y
XB
XB
XBXb XBXb
XBY XBY
Genotypic ratio
50% XBXb
50% XBY
Phenotypic ratio
50% female tortoiseshell
50% male black
b) Is it possible to get a male tortoiseshell cat? Explain.
No, it is not possible because the alleles are on the X chromosome and you need both a B
and b allele to get tortoiseshell. Since the male can only have one X chromosome, he will
not have a tortoiseshell phenotype.
7. Sickle cell anemia is a genetic disease which causes malformation of the red blood cells (some
of them collapse into a sickle shape). It is caused by one gene only. Individuals who are
homozygous for sickle cell anemia tend to die as small children, by hybrids (“carriers”) suffer
much less and often live long enough to reproduce.
a) If a male carrier is crossed with a female carrier, what is the probability of having a child with
the actual disease?
Punnett Square
A
a
Probability of a child with the disease
25% chance (aa)
A
a
AA Aa
Aa aa
b) Is sickle cell anemia a sex-linked trait? How can you tell?
No. There is a male carrier, which is not possible in sex-linked traits.
c) Is the gene for sickle cell anemia dominant or recessive? Explain.
Recessive because there are carriers. If it were dominant, any individual with the allele
would have the disease.
8. Gene Interaction: In the budgerigar bird, blue colour (B) is incompletely dominant over yellow
colour (Y). Heterozygous birds are (BY) are green. In addition, long wings (S) are dominant
over short wings (s).
a) Cross a long-winged, blue bird (SsBB) with a long-winged, green bird (SsBY) using the 16-box
Punnett square.
SB
SB
sB
sB
SB
SSBB
SSBB
SsBB
SsBB
SY
SSBY
SSBY
SsBY
SsBY
sB
SsBB
SsBB
ssBB
ssBB
sY
SsBY
SsBY
ssBY
ssBY
b) What is the phenotypic ratio of the offspring?
6 Blue, long-winged  3
6 Green, long-winged  3
2 Blue, short-winged  1
2 Green, short-winged  1