Moreen Mero BTEC Applied Science L3 Unit 11 Assignment 3 2020/2021
PART A
Virtual 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 the 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 HOMOZYGOUS – two copies of the
normal allele (BB) ebony allele (bb)
HETEROZYGOUS - one copy of the
normal allele and one copy of the 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).
Updated, WHC: June 2017
, Moreen Mero BTEC Applied Science L3 Unit 11 Assignment 3 2020/2021
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
F2 Offspring genotype F2 Offspring
phenotype
Bb Normal fly
Bb Normal fly
BB Normal fly
Bb Normal fly
bb Ebony fly
Bb Normal fly
Bb Normal fly
Bb Normal fly
BB Normal fly
Bb Normal fly
2. Total the number of each type of body and work out the ratio of ebony to normal
bodies.
Normal body Ebony Body
9 1
RATIO:
9:1
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
Updated, WHC: June 2017
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