BY 123 SI Session #9
Chapter 14
1) A tall pea plant is crossed with a recessive dwarf pea plant. What will the phenotypic and
genotypic ratio of offspring be if :
a. The tall plant was TT?
Phenotype = tall plant
Genotype: Tt
b. The tall plant was Tt.
Phenotype = 2 tall, and 2 dwarf
Genotype: Tt and tt
2) A true-breeding tall, purple flowered pea plant (TTPP) is crossed with a true-breading dwarf,
white-flowered plant (ttpp).
a. What is the phenotype of the F1 generation?
Tall and Purple
b. What is the genotype of the F1 generation?
TtPp
c. What four types of gametes are formed by F1 plants?
TP, Tp, tP, and tp
d. Fill in a Punnett square to show the offspring of the F2 generation. Use stars, squares,
circles, and hearts to show the ratio differences.
TTPP
TTPp
TtPP
TtPp
TTPp
TTpp
TtPp
Ttpp
TtPP
TtPp
TtPp
Ttpp
ttPP
ttPp
ttPp
ttpp
e. List the phenotypes and ratios found in the F2 generation.
9:3:3:1 ratio
9= tall purple
3 = tall white
3= dwarf purple
1 = dwarf white
3) Suppose you crossed a Blue Unicorn (CBCB) with a Yellow Unicorn (CYCY). Show the punnett
square of the F2 generation assuming the incomplete dominance plays a role in the cross.
CBCB
CBCY
CBCy
CyCy
1 Blue
2 Green (the mixture )
3 Yellow
4) Suppose that epistasis plays a role in a cross between two black rats (RrEe) who are
heterozygous for both the Black gene (Bb) and the pigment gene (Ee). Make a punnett square
and show the genotypes of the offspring of the F2 cross. The pigment gene must have one
dominant allele in order to show color. B=black, b=brown, E=pigment, e= no pigment .
RREE
RREe
RrEE
RrEe
RREe
RrEe
RrEE
RrEe
RrEE
rrEe
RRee
Rree
RrEe
RrEe
Rree
Rree
5) Suppose that codominance plays a role in a cross between a white rat with speckles (WsWs) and
a white rat with patches (WpWp). Make a punnett square and show the F2 cross between these
two rats. Which would show both traits? Which would show only speckles or only patches?
W PW P
WpWs
The WpWs would show both traits( 2 total).
Ws Wp
Ws Ws
6) Match the following Relationship to its description:
__a____ Heterozygous phenotype same as that of homozygous dominant
__b___ Heterozygous phenotype intermediate between the two homozygous phenotypes
___e___ One gene is able to affect multiple phenotypic characters
____f__ The phenotypic expression of one gene affects that of another
_____c_ Both phenotypes expressed in heterozygous
__g____ A single phenotypic character is affected by two or more genes
___d____ In the whole population, some genes have more than two alleles
Word Bank:
a. Complete dominance of one allele
b. Incomplete dominance of one allele
c. Codominance
d. Multiple alleles
e. Pleiotrophy
f. Epistasis
g. Polygenic inheritance
7) Fill in the Chart Below for Dominant and Recessive genetic conditions:
Dominantly Inherited Disorders
Recessively Inherited Disorders
Huntington’s
Albanism
Achondroplasia
Cystic Fibrosis
Sickle Cell disease