FISH
Genetics
PART
B
Teacher’s Instructions:
1) This is Part B of a three-part (A, B, C) project about Fish Genetics. Even if you do not
wish to complete the entire project, you may still use Part B as a stand-alone activity.
In this part, students will learn about Punnett squares and pedigree charts.
2) Hand out pages 2 to 13 to each student.
3) Students will read pages 2 to 8 and answer the questions on pages 9 to 13.
4) You may collect the question sheets for assessment or correct them in class.
An answer key is provided on pages 14 to 18.
5) If you would like to show the students a fish karyotype, please see the activity entitled
‘Chromosome Mapping’ from Grade 9 (http://www.gov.mb.ca/conservation/sustain/9.html)
References:
Dunham, R., Norgren, K., Robison, L., Smitherman, R., Steeger, T., Peterson, D., et al. (1994).
Hybridization and Biochemical Genetics of Black and White Crappies in the
Southeastern USA. Transactions of the American Fisheries Society, 123, 141-149.
Problem 5: Interpreting a pedigree chart. (1998). Human Genetics Problem Set. Retrieved
November 3, 2005 from http://www.biology.arizona.edu/human_bio/problem_sets/
human_genetics/05Q.html
Manitoba Education Training and Youth (2006). Introduction to Genetics. Senior 4
Biology (40S) Web CT Course.
white sucker
black
crappie
1
FISH
Genetics
PART
B
PART B: SQUARE DANCE (Grab your partner!)
Objectives:
1) To use Punnett squares to solve a variety of inheritance problems and justify the results
by using appropriate terminology.
2) To use pedigree charts to illustrate the inheritance of genetically determined traits.
Tasks:
1) Read pages 2 to 8 and complete the examples found on these pages.
2) Answer the questions on pages 9 to 13.
Key Terms:
- autosomal:
a trait (genes) that is (are) found on chromosomes (except sex
chromosomes).
- Punnett square: a type of grid that indicates all the possible outcomes of a genetic
cross and can be used to determine probabilities of offspring inheriting
certain characteristics for specific traits.
- pedigree chart: a diagram that illustrates the inheritance pattern of characteristics for
specific traits in a family tree and can be used to determine the
probability of certain offspring in different generations having particular
characteristics for those traits.
Punnett Squares
Pedigree Chart
R
R
r
Rr
Rr
r
Rr
Rr
R
r
R
RR Rr
r
rR
rr
2
FISH
Genetics
PART
B
Background:
Punnett squares can be used to calculate all the possible outcomes of a genetic
cross. These squares also show the probability of different genotypes and phenotypes.
For example, a monohybrid (one trait with two alleles) cross between two homozygous
sucker fish (one light-scaled and one dark-scaled) would produce the following Punnett
square:
LL x ll
L
l
l
Ll
Ll
white sucker
L
Ll
Ll
This Punnett square shows that all of the offspring would have a heterozygous genotype
of Ll. All of the offspring would have a phenotype of light coloured scales.
Two light-coloured heterozygous suckers are crossed in the following Punnett square:
Ll x Ll
L
l
L
LL Ll
l
lL
ll
This Punnett square shows the probabilities of the genotypes for this cross as follows:
1/4 are LL (homozygous dominant),
1/2 are Ll (heterozygous dominant), and
1/4 are ll (homozygous recessive).
This Punnett square also shows the probabilities of the phenotypes for this cross:
3/4 have light coloured scales and
1/4 have dark coloured scales.
Note that this a 3:1 ratio (just as Mendel discovered).
3
Genetics
FISH
PART
B
Background (continued...):
Punnett squares can also be used for dihybrid crosses. A dihybrid cross involves two
traits with two alleles each. For example, black and white crappies can be crossed and
we can examine two traits (colouring and number of spines) of the offspring. When black
and white crappies are crossed, the dominant colouring is black (B) and the dominant
number of spines is 7 (S). Let’s create a Punnett square for a pure-bred black crappie
with 7 spines crossed with a pure-bred white crappie with 5 spines. Remember that one
trait will have no effect on the inheritance of another trait (Mendel’s Law of Independent
Assortment).
Step 1) Determine the genotype of each parent.
- Pure-bred black crappie with 7 spines. Black colouring and 7
spines are dominant so this fish will have a genotype of BBSS.
- Pure-bred white crappie with 5 spines. White colouring and 5 spines
are recessive so this fish will have a genotype of bbss.
Step 2) Determine the possible genetic recombinations for each parent.
BBSS
BS BS BS BS
b b s s
bs
bs
bs bs
\
Step 3) Calculate possible offspring using the Punnett square.
BS
BS
BS
BS
bs
BbSs BbSs BbSs BbSs
bs
BbSs BbSs BbSs BbSs
bs
BbSs BbSs BbSs BbSs
bs
BbSs BbSs BbSs BbSs
black
crappie
Step 4) Interpret the Punnett square.
- All of the offspring will have a genotype of BbSs.
- All of the offspring will have a phenotype of black colouring and 7 spines.
4
Genetics
FISH
PART
B
Background (continued...):
Let’s create a Punnett square for another dihybrid cross: between two black crappies
that are heterozygous for both traits (colouring and number of spines).
Step 1) Determine the genotype of each parent.
- Both parents will have the same genotype. A heterozygous black crappie
with seven spines will have a genotype of BbSs.
Step 2) Determine the possible genetic recombinations for each parent. (Both will be
the same in this case.)
Bb S s
BS Bs bS bs
Bb S s
BS Bs bS bs
Step 3) Calculate possible offspring using the Punnett square.
BS
Bs
bS
bs
BS
BBSS BBSs BbSS BbSs
Bs
BBSs BBss BbSs Bbss
bS
BbSS BbSs bbSS bbSs
bs
BbSs Bbss
Step 4) Interpret the Punnett square.
- Genotypic Probabilities:
- 1/16 has BBSS
- 2/16 have BBSs
- 2/16 have BbSS
- 1/16 has BBss
- 4/16 have BbSs
- 2/16 have Bbss
- 1/16 has bbSS
- 2/16 have bbSs
- 1/16 has bbss
bbSs bbss
- Phenotypic Probabilities:
- 9/16 are black with 7 spines
- 3/16 are black with 5 spines
- 3/16 are white with 7 spines
- 1/16 are white with 5 spines
5
Genetics
FISH
PART
B
Background (continued...):
A pedigree chart is a diagram that shows the phenotypic characteristics of a trait that
is inherited from generation to generation. Squares represent males and circles represent
females. A shaded square or circle means that the individual has a specific characteristic
for the trait being studied. Unshaded squares or circles represent individuals that do not
have the specific characteristic for the trait being studied. Horizontal lines join pairs that
have mated. Vertical lines join offspring to their parents. Roman numerals are used to
indicate generations. Numbers may be used to indicate birth order. Individuals can be
identified in the pedigree using this information. For example, individual I-2 would be the
second born individual in the first generation. In this pedigree chart, this individual is the
mother.
Generation
number
I-2
I
mated
1
malehas trait
being studied
2
female
black
crappie
offspring
II
birth order
1
2
3
female has trait
being studied
male
female
Two individuals, the father (I - 1) and the first born offspring (II-1), have the same
characteristic for the trait that is being studied in this pedigree. The unshaded individuals
do not have the characteristic for the trait that is being studied.
Pedigree charts can also be used to determine genotypes. For example, assume the
above pedigree chart is studying the characteristic of white coloured scales on crappies
from crosses between white and black crappies. White coloured scales is a characteristic
for the scale colour trait in crosses between white and black crappies. We know that white
coloured scales (b) is a recessive trait. Therefore, the genotypes for I-1 and II-1 must be bb
because they are both expressing the characteristic for the trait being studied. Next, we
can look to the mother (I-2). She can either have a genotype of BB or Bb (since she is not
expressing the recessive characteristic). If she has a genotype of BB then all of her
offspring would have at least one B in their genotypes. Since one of her offspring has a
genotype of bb, she must have given that offspring one b. Therefore, her genotype must
be Bb. Lastly, we can determine the genotypes of II-2 and II-3. These offspring must
have one b from their father. However, since they are not expressing the recessive
characteristic, they must also have a B. We know this is possible since their mother’s
genotype is Bb and therefore it is possible for her to give her offspring a B. So, we
conclude that these offspring have genotypes of Bb.
6
Genetics
FISH
PART
B
Background (continued...):
Here is another pedigree chart in which the white recessive characteristic of the
colouring of crappies is being studied. Let’s determine the genotypes of each individual
in this chart. Note that there may be certain situations where the exact genotype is
impossible to determine from the pedigree chart alone.
1
I
1
II
III
1
2
2
2
4
3
3
5
4
Since we know that this pedigree is identifying the recessive individuals for this trait as
shaded, individuals that are expressing this characteristic have two recessive alleles (bb).
Thus, we can label the following individuals with bb genotypes: I-2, II-4 and III-1. (You
may wish to write these genotypes underneath each individual in the chart.) We also
know that each of the non-shaded figures have 1 of 2 genotypes: BB or Bb since they
are displaying the dominant characteristic.
Next, we notice that I-1 and I-2 have three offspring and that one of these offspring is
homozygous recessive (II-4). This means that this offspring received one recessive allele
from each parent. Thus, I-1 must have a genotype of Bb so that one b can be passed
on to its offspring (II-4).
Individuals II-2 and II-3 must have a genotype of Bb since they can only receive a b
from their mother (and they must have a B from the parent expressing the dominant
characteristic. By the same reasoning, individuals III-3, and III-4 must also have Bb
genotypes.
Individual II-1 must have a genotype of Bb since it must give a b to III-1 and it must
have a B because it is not expressing the characteristic.
We know that II-5 and III-2 must have at least one B but their full genotypes are
unknown since it is possible for both of these individuals to give or receive either a B or b
allele. We can write their genotypes as B_.
Notice that in this pedigree chart, the recessive characteristic is not seen in successive
generations and is sometimes seen in an offspring of two parents who are not expressing
the recessive characteristic. This is normally the case with autosomal recessive traits.
7
Genetics
FISH
PART
B
Background (continued...):
This pedigree chart is studying the dominant characteristic of black colouring of
crappies. Let’s determine the genotypes of each individual in this chart. Note that there
may be certain situations where the exact genotype is impossible to determine from the
pedigree chart alone.
1
I
1
II
III
1
2
2
2
4
3
3
5
4
Since we know that this pedigree chart is studying a dominant trait, we know that all of
the individuals that are not expressing the trait (not shaded) have two recessive alleles (bb).
Thus, we can label the following individuals with bb genotypes: I-1, II-1, II-3, II-5 and III-2.
(You may wish to write these genotypes underneath each individual in the chart.) We
also know that each of the shaded figures have 1 of 2 genotypes: BB or Bb since they
are displaying the dominant characteristic.
Next, we notice that I-1 and I-2 have three offspring and that one of these offspring
is homozygous recessive. This means that this offspring received one recessive allele
from each parent. Thus, I-2 must have a genotype of Bb so that one b can be passed
on to its offspring (II-3).
Individuals II-2 and II-4 must have a genotype of Bb since they can only receive a b
from their father (and they must have a B from their mother since they are expressing the
dominant characteristic). By the same reasoning, individuals III-1, III-3 and III-4 must
also have Bb genotypes.
Notice that in this pedigree chart, the trait is seen in successive generations and is
passed from fathers to daughters and/or sons. This is normally the case with autosomal
dominant traits.
8
FISH
Genetics
PART
B
Questions:
1) Complete and interpret the following Punnett squares. Give the ratios (fractions) of
each genotype and phenotype.
a)
A homozygous black crappie crossed with a white crappie. Black colouring (B)
is the dominant allele.
Genotypes
Phenotypes
b) A dark-scaled sucker and a heterozygous light-scaled sucker. Light-scaled (L) is
the dominant allele.
Genotypes
Phenotypes
c) Two heterozygous light-scaled suckers.
Genotypes
Phenotypes
9
FISH
Genetics
PART
B
d) A black crappie heterozygous for colour and homozygous for 7 spines and
a black crappie heterozygous for colour and heterozygous for 7 spines.
Genotypes
Phenotypes
e) A white crappie heterozygous for 7 spines and a black crappie heterozygous
for colour and with 5 spines.
Genotypes
black
crappie
Phenotypes
10
FISH
Genetics
PART
B
2) Use the following pedigree chart to answer the questions below and on page 12.
1
I.
II.
III.
1
3
2
2
1
3
2
4
4
3
5
5
4
6
6
7
a) Circle the appropriate gender for each of the following:
I-4
male
female
III - 5
male
female
II - 6
male
female
I-1
male
female
III - 3
male
female
black
crappie
b) How many individuals have the trait being studied? _____
How many females have the trait being studied?
_____
How many males have the trait being studied? _____
Which individuals have the trait being studied? ______________________________
11
FISH
Genetics
PART
B
c) Write down the appropriate relationship between the following individuals. The
first one has been done for you.
III - 5 and III - 7
brother and ____________
sister
____________
I - 1 and III - 3
___________ and ____________
III - 2 and II - 1
___________ and ____________
II - 2 and II - 3
___________ and ____________
d) Is the autosomal trait being studied dominant or recessive? _______________
How do you know?
e) Assume this pedigree chart is for the trait that determines the number of spines
on a crappie. The gene for seven spines is dominant (S) and the gene for five
spines is recessive (s). Find the genotype for each individual of the pedigree
chart (if possible). Write your answers next to each individual on the pedigree
chart.
3) Design and construct an autosomal recessive pedigree chart for the following family:
A dark-scaled sucker mates with a light-scaled sucker. They have 6 offspring:
4 males and 2 females. One of the female offspring is dark-scaled. One
dark-scaled male offspring finds a light-scaled mate and together they have
5 offspring: 4 females and 1 male. All of these offspring are light-scaled.
12
Genetics
FISH
PART
B
4) Determine if the following pedigree chart is autosomal dominant or autosomal
recessive and then fill in the genotypes (if possible). Assume the trait being studied is
colour of scales on suckers. (Light colouring is dominant and dark colouring is recessive).
1
I
2
white sucker
II
III
1
3
2
1
2
4
4
6
3
5
5
5) Design and construct a pedigree chart of your family or a family you know. Be sure to
include at least 12 individuals and 3 generations. Select one characteristic from the
list of traits (below) to study.
Characteristics
Trait
Dominant
Recessive
earlobes
free
attached
hairline
widow’s peak
smooth
dimples
dimples
no dimples
thumbs
straight
curved
roller
non-roller
tongue-rolling
13
FISH
Genetics
PART
B
Answer Key:
1) Complete and interpret the following Punnett squares. Give the ratios (fractions) of
each genotype and phenotype.
a)
A homozygous black crappie crossed with a white crappie. Black colouring (B)
is the dominant allele.
BB x bb
B
B
Genotypes
all Bb
b
Bb
Bb
b
bB
bB
Phenotypes
all black colour
b) A dark-scaled sucker and a heterozygous light-scaled sucker. Light-scaled (L) is the
dominant allele.
ll x Ll
l
l
L
Ll
Ll
l
ll
ll
Genotypes
Phenotypes
½ Ll
½ light-coloured
½ ll
½ dark-coloured
c) Two heterozygous light-scaled suckers.
Ll x Ll
L
L
l
LL
Ll
Genotypes
Phenotypes
1/4 LL
3/4 light-scaled
½ Ll
1/4 dark-scaled
1/4 ll
l
lL
ll
14
Genetics
FISH
PART
B
d) A black crappie heterozygous for colour and homozygous for 7 spines and
a black crappie heterozygous for colour and heterozygous for 7 spines.
BbSS x BbSs
BS
BS
Genotypes
bS
bS
2/16 BBSS
BS
BBSS BBSS BbSS BbSS
4/16 BbSS
Bs
BBSs BBSs BbSs BbSs
2/16 BBSs
bS
BbSS BbSS bbSS bbSS
Phenotypes
12/16 black colour,
7 spines
4/16 white colour,
7 spines
4/16 BbSs
2/16 bbSS
bs
BbSs BbSs bbSs
bbSs
2/16 bbSs
e) A white crappie heterozygous for seven spines and a black crappie heterozygous
for colour and with five spines.
bbSs x Bbss
bS
Bs
Bs
bs
bs
bs
bS
BbSs Bbss BbSs
Genotypes
bs
4/16 BbSs
4/16 black colour,
7 spines
4/16 Bbss
4/16 black colour,
5 spines
4/16 bbSs
4/16 white colour,
7 spines
4/16 bbss
4/16 white colour,
5 spines
Bbss
BbSs Bbss BbSs Bbss
bbSs bbss bbSs
bbss
bbSs bbss bbSs bbss
Phenotypes
black
crappie
15
FISH
Genetics
PART
B
2) Use the following pedigree chart to answer the questions below and on page 12.
1
2
3
4
Ss
Ss
Ss
ss
1
2
3
4
5
6
S_
ss
Ss
ss
Ss
Ss
I
II
III
1
2
3
4
5
6
7
Ss
Ss
ss
Ss
S_
ss
S_
1.
a) Circle the appropriate gender for each of the following:
I-4
male
female
III - 5
male
female
II - 6
male
female
I-1
male
female
III - 3
male
female
black
crappie
5
b) How many individuals have the trait being studied? _____
How many females have the trait being studied?
3
_____
How many males have the trait being studied? _____2
I-4, II-2, II-4, III-3, III-6
Which individuals have the trait being studied? ______________________________
16
FISH
Genetics
PART
B
c) Write down the appropriate relationship between the following individuals. The
first one has been done for you.
III - 5 and III - 7
brother and ____________
sister
____________
grandmother
___________ and granddaughter
____________
III - 2 and II - 1
son and ____________
father
___________
II - 2 and II - 3
___________
sister and ____________
sister
I-1
and
III - 3
recessive
d) Is the autosomal trait being studied dominant or recessive? _______________
How do you know?
Because two different sets of parents without the trait
have offspring with the trait.
e) Assume this pedigree chart is for the trait that determines the number of spines
on a crappie. The gene for seven spines is dominant (S) and the gene for five
spines is recessive (s). Find the genotype for each individual of the pedigree
chart (if possible). Write your answers next to each individual on the pedigree
chart.
3) Design and construct an autosomal recessive pedigree chart for the following family:
A dark-scaled sucker mates with a light-scaled sucker. They have 6 offspring:
4 males and 2 females. One of the female offspring is dark-scaled. One
dark-scaled male offspring finds a light-scaled mate and together they have
5 offspring: 4 females and 1 male. All of these offspring are light-scaled.
I.
II.
III.
17
Genetics
FISH
PART
B
4) Determine if the following pedigree chart is autosomal dominant or autosomal
recessive and then fill in the genotypes (if possible). Assume the trait being studied is
colour of scales on suckers. (Light colouring is dominant and dark colouring is recessive).
Dominant
I
II
III
1
2
ll
Ll
1
2
Ll
Ll
white sucker
3
4
6
5
L_
ll
ll
L_
1
2
4
3
5
ll
ll
Ll
ll
ll
5) Design and construct a pedigree chart of your family or a family you know. Be sure to
include at least 12 individuals and 3 generations. Select one characteristic from the
list of traits (below) to study.
Characteristics
Trait
Dominant
Recessive
earlobes
free
attached
hairline
widow’s peak
smooth
dimples
dimples
no dimples
thumbs
straight
curved
roller
non-roller
tongue-rolling
Answers will vary.
18