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Unit 11 A3 Learning aim C: Explore the principles of inheritance and their application in predicting genetic traits
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- PEARSON (PEARSON)
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PART AVirtual fruit fly breeding experiment
Monohybrid inheritance (one characteristic)
Fruit flies are normally brown but a mutation exists that produces a fly that has an ebony body.
The normal brown allele is DOMINANT (B) and ebony allele is RECESSIVE (b).
Normal body Ebony body
Normal body flies can be either: Flies with ebony bodies must be:
HOMOZYGOUS – two copies of the normal HOMOZYGOUS – two copies of the ebony
allele (BB) allele (bb)
HETEROZYGOUS - one copy of the normal
allele and one copy of ebony allele (Bb)
Experiment 1
A homozygous normal body male fly is crossed with an ebony body female fly: The cross is shown as:
Genotype BB bb
Gametes B b
Offspring genotype Bb
Offspring phenotype (F1) Normal body
The F1 offspring are all heterozygous. Simulate their crossbreeding by performing the experiment.
Crossing the F1 generation
Place a red dot on the belly of 5 flies (representing the B allele) and yellow dots on 5 flies (representing the
b allele) .
1. Blindly pick out a fly one at a time and fill out the table below to show the possible outcome of
offspring. Write in the phenotype (normal or ebony) at the side of the pair of alleles that make the
genotype
Updated, WHC: June 2017
, F2 Offspring genotype F2 Offspring phenotype
BB Normal
Bb Normal
bb Ebony
Bb Normal
bb Ebony
BB Normal
Bb Normal
bb Ebony
Bb Normal
BB Normal
2. Total the number of each type of body and work out the ratio of ebony to normal bodies.
Normal body Ebony Body
7 3
RATIO:
7:3
3. Work out the theoretical ratio using the Punnett square below:
Parental B b
genotypes
B BB Bb
Bb bb
b
4. Total the number of each type of body (phenotype) and work out the theoretical ratio of ebony to normal
bodies.
Normal body Ebony Body
3 1
RATIO:
3:1
5.Compare the two phenotypic ratios that you have obtained (ratio from virtual experiment and ratio
from punnet square). Comment on whether your results from the virtual experiment are as you have
predicted using the above Punnett square. (This section should also include photographic evidence of your
fly experiment)
Using Mendel’s laws, independent assortment is when the genes alleles particularly are inherited independently,
as its able to segregate from each other, this unique combination of the chromosomes in the gametes, as such
will result in different physical properties of the flies. We can predict the gene as well another gene which
wouldn’t be necessary to know so we live it aside. Then, the law of segregation can help to figure out that the
parent fly is able to pass one allele to its offspring, as so using the law of dominance will help to predict which
allele will cross over with each other, it will show if its heterozygous as so the differences can be shown through
Updated, WHC: June 2017
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