Investigating Albinism in Barley Plants
There is a gene controlling pigment production in barley that has the alternate alleles:
A: pigment produced-green (dominant)
a: no pigment-albino (or white) - (recessive)
where pigment production is dominant to albino.
The seeds planted were produced from crossing heterozygous plants for the gene concerned (Aa x Aa).
1. Approximately 35 seeds were germinated by placing them on moistened cotton wool in a small petri dish.
2. The petri dishes were placed in a warm environment of approximately 22-24 C degrees.
3. The cotton wool was kept moist for 6 days and on day 6 the number of seedlings was counted.
4. The seedlings were assessed as either containing chlorophyll or not containing chlorophyll when they had reached a height of 4-5 cm.
Results: ...view middle of the document...
This prediction resolves from the fact that some of the plants were also green which means that the genotypes could not have been homozygous recessive as this would have only given rise to albino plants.Â The genotype of the albino plants must be homozygous recessive (aa) as the albino allele is recessive to the green/chlorophyll allele. The genotype of the green plants could either be heterozygous (Aa) or homozygous dominant (AA) as both of these allele combinations give rise to green plant, due to the green allele being dominant over the albino allele.
If a larger number of seedlings were obtained the approximate color ratio would be expected to be 3:1 as this is the expected ratio of offspring when two heterozygous organisms breed together.
Green (A) is the dominant allele. The effect of this was seen in the experiment as the majority of the plants were green.
The punnett square above shows all the possible offsprings. It shows that the possible genotypes for green plants are either AA or Aa.
The genotype of a green barley plant can be determined with the help of a test cross. This is by mating it with an albino plant. If the offsprings are all green the barley plant almost certainly is homozygous dominant (AA). Unless there is a large number of offspring though, this could also happen if the genotype is heterozygous (Aa) but, just by chance, none of its gametes carrying the recessive allele were successful in fertilization. If there are both green and albino the plants the genotype is definitely heterozygous (Aa). The albino plants might fail to thrive as they miss the gene for producing chlorophyl. This resolves in them not being able to produce food for themselves as they do this with the process of photosynthesis which requires chlorophyl to work. In conclusion the experiment proves that the seeds planted were produced from crossing heterozygous plants. It also shows that when crossing heterozygous plants the ratio is almost certainly close to Mendel's theory of 3:1.