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ZOL2602 Assignment 2
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- University Of South Africa (Unisa)
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Assignment number: 214879ZOL2602
ASSIGNMENT 2
Nicole Price
17653800
, N.P - 17653800
Question 1
1.1 Mendel used pea plants to show how inherited characteristics are passed from
parent plants to its offspring. He used various characteristics, such as pea shape
and/or colour to simply describe the phenotypes of peas. In his experiment, he first
began to self-fertilise a pea plant, which always resulted in giving offspring that
resembled the characteristics of the parent plant. These would therefore be pure
breeding by either being wrinkled or round. By using a punnet square, he was able to
visually show the plants resulting genotypes and the phenotypes of its offspring (F1
generation). Next, he self-fertilised the resulting offspring to work out the next
generation, F2. This gave a 1:3 ratio of wrinkled and round peas. Mendel explained
that this result is due to each characteristic being controlled by a unit factor (a gene),
with each being able to have more than one form, which is now referred to as alleles.
By doing these crosses, Mendel realised that there must be two alleles present in the
F1 plants as one of the parental characteristics is lost in the resulting F1 generation
but reappears in the F2 generation. Therefore, he concluded that a gene must have
two alleles present and occur in pairs (eg: the F1 generation genotype being shown
as R and r= Rr). This gave rise to the alleles either being dominant or recessive, with
dominance always being favoured in heterozygote outcomes. The results are split
into four possible combinations: ‘RR’ (Dominant round shape), ‘Rr’ (Dominant round
shape) and ‘rr’ (recessive wrinkled shape). Each offspring has obtained one allele
from the F1 plants and this is proven through having the recessive ‘rr’ outcome,
which could only arise from one ‘r’ being passed from each F1 parent plant.
Therefore, intermediate or heterozygotes can be formed during random segregation
resulting in the genotype ‘Rr’. The final genotype outcome of a ‘Rr’ heterozygote
crossed with either a ‘RR’ homozygote or another heterozygote ‘Rr’, the F2 would
result in the genotypes 1RR : 2Rr : 1rr and the phenotype being 1 wrinkled to 3 round
shaped peas.
2.1 Phenotypes: Shape: Full/Constricted ; Colour: Yellow/Green
Genotypes: Full= A , Constricted= a ; Green= B , Yellow=b
Parents (P1): AABB = full green pods and aabb = constricted yellow pods
Parents (P1) gametes: AB AB and ab ab
AB AB AB AB
ab AaBb AaBb AaBb AaBb
ab AaBb AaBb AaBb AaBb
1
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