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GeneticsFISH PART
B
1
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
GeneticsFISH
Objectives:
Tasks:
Key Terms:
PART B: SQUARE DANCE (Grab your partner!)
1) Read pages 2 to 8 and complete the examples found on these pages.2) Answer the questions on pages 9 to 13.
- autosomal: a trait (genes) that is (are) found on chromosomes (except sex chromosomes).- Punnett square:
- 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.
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.
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.
Punnett Squares
R
r
R
r
R
r
R
r
Rr
Rr
Rr
Rr
RR Rr
rR rr
Pedigree Chart
2
PART
B
3
Background:
GeneticsFISH
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
This Punnett square shows that all of the offspring would have a heterozygous genotypeof 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
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).
l
L
l
L L l
L l
L l
L l
L
l
l
L L L
l L
L l
l l
PART
B
white sucker
4
GeneticsFISH
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 andwe 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.
B B S S b b s s
\ Step 3) Calculate possible offspring using the Punnett square.
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.
PART
B
BS BS BS BS
bs
bs
bs
bs
BbSs BbSs BbSs
BbSs BbSs BbSs
BbSs
BbSs
BbSsBbSsBbSs
BbSs BbSs BbSs
BbSs
BbSs
black crappie
BS BS BS BS bs bs bs bs
5
GeneticsFISH
Background (continued...):
Let’s create a Punnett square for another dihybrid cross: between two black crappiesthat 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.)
B b S s B b S s
Step 3) Calculate possible offspring using the Punnett square.
Step 4) Interpret the Punnett square. - Genotypic Probabilities: - Phenotypic Probabilities:
- 1/16 has BBSS - 9/16 are black with 7 spines
- 2/16 have BBSs - 3/16 are black with 5 spines
- 2/16 have BbSS - 3/16 are white with 7 spines
- 1/16 has BBss - 1/16 are white with 5 spines
- 4/16 have BbSs - 2/16 have Bbss - 1/16 has bbSS - 2/16 have bbSs - 1/16 has bbss
PART
B
BS Bs bS bs
BS
Bs
bS
bs
BBSS BBSs BbSS
BBSs BBss BbSs
BbSs
Bbss
bbSsbbSSBbSs
Bbss bbSs bbss
BbSS
BbSs
BS Bs bS bs BS Bs bS bs
black crappie
GeneticsFISH PART
B
6
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 characteristicfor 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.
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 individualsdo 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 characteristicfor 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 notexpressing 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.
I
II1 2 3
1 2
male-has trait
being studied
malefemale - has trait
being studied
female
female
mated
offspring
Generationnumber
birth order
I-2
GeneticsFISH
7
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.
Since we know that this pedigree is identifying the recessive individuals for this trait asshaded, 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 bfrom 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.
I
II
III
1 2
5
1 2
3 41 2
3 4
GeneticsFISH
8
PART
B
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.
Since we know that this pedigree chart is studying a dominant trait, we know that all ofthe 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 theyare displaying the dominant characteristic. Next, we notice that I-1 and I-2 have three offspring and that one of these offspringis 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 bfrom 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.
Background (continued...):
I
II
III
1
2
3 4
2
5
1 2
3 41
GeneticsFISH PART
B
9
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.
b) A dark-scaled sucker and a heterozygous light-scaled sucker. Light-scaled (L) is the dominant allele.
c) Two heterozygous light-scaled suckers.
Genotypes Phenotypes
Genotypes Phenotypes
Genotypes Phenotypes
GeneticsFISH
10
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.
e) A white crappie heterozygous for 7 spines and a black crappie heterozygous for colour and with 5 spines.
Genotypes Phenotypes
Genotypes Phenotypes
black crappie
GeneticsFISH PART
B
11
I.
II.
2) Use the following pedigree chart to answer the questions below and on page 12.
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
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? ______________________________
III. 1 2 4
1 2 3 4
1 2 3 4
5 6
75 63
black crappie
12
GeneticsFISH PART
B
c) Write down the appropriate relationship between the following individuals. The first one has been done for you.
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.
I - 1 and III - 3 ___________ and ____________
II - 2 and II - 3 ___________ and ____________
III - 5 and III - 7____________ and ____________
III - 2 and II - 1 ___________ and ____________
brother sister
GeneticsFISH
13
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).
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.
I
II
III 1 2 3 5
1 2 44
4
6
2
5
1
3
white sucker
Characteristics
Trait Dominant Recessive
earlobes free attached
hairline widow’s peak smooth
dimples dimples no dimples
thumbs straight curved
tongue-rolling roller non-roller
GeneticsFISH PART
B
14
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.
b) A dark-scaled sucker and a heterozygous light-scaled sucker. Light-scaled (L) is the dominant allele.
c) Two heterozygous light-scaled suckers.
Genotypes Phenotypes
Genotypes Phenotypes
Genotypes Phenotypes
BB x bb
B
b
b
B
BbBb
bBbB
all Bb all black colour
ll x Ll
l
L
l l
Ll
ll
Ll
ll
½ Ll ½ light-coloured
½ ll ½ dark-coloured
Ll x Ll
L
l
L l
lL
LL Ll
ll
1/4 LL 3/4 light-scaled
½ Ll 1/4 dark-scaled
1/4 ll
GeneticsFISH
15
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.
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
Bs
BBSS BBSS BbSS BbSS
BBSs BBSs BbSs BbSs
BbSS BbSS bbSS bbSS
BbSs BbSs bbSs bbSs
Genotypes Phenotypes
bbSs x Bbss
bS bs bS
bs
bs
bs
Bs
Bs
BbSs Bbss BbSs Bbss
BbSs Bbss BbSs Bbss
bbSs bbss bbSs bbss
bbSs bbss bbSs bbss
Genotypes Phenotypes
2/16 BBSS 4/16 BbSS
2/16 BBSs
4/16 BbSs
2/16 bbSS
2/16 bbSs
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
black crappie
12/16 black colour, 7 spines
4/16 white colour, 7 spines
GeneticsFISH PART
B
16
I
II
1.
2) Use the following pedigree chart to answer the questions below and on page 12.
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
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? ______________________________
III 1 2 4
1 2 3 4
6
1 2 3 4
5 6
753
5
3
2
I-4, II-2, II-4, III-3, III-6
SsSsSs
Ss
ss
Ss
ss
Ss
ss
Ss
ss
Ss
ss
Ss
S_
S_
S_
black crappie
17
GeneticsFISH PART
B
c) Write down the appropriate relationship between the following individuals. The first one has been done for you.
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.
I - 1 and III - 3 ___________ and ____________
II - 2 and II - 3 ___________ and ____________
grandmother granddaughter
sister sister
recessive
Because two different sets of parents without the trait have offspring with the trait.
I.
II.
III.
III - 5 and III - 7____________ and ____________
III - 2 and II - 1 ___________ and ____________
brother sister
son father
GeneticsFISH
18
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).
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.
I
II
III 1 2 3 5
1 2 44
4
6
2
5
Answers will vary.
Dominant
ll
ll ll llll
ll
Ll
L_Ll ll
Ll
Ll
1
3
white sucker
L_
Characteristics
Trait Dominant Recessive
earlobes free attached
hairline widow’s peak smooth
dimples dimples no dimples
thumbs straight curved
tongue-rolling roller non-roller
