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Explain any two of the following terms: Lethal gene Recessive gene Sex-linked gene - Leaving Cert Agricultural Science - Question 7 - 2009
Question 7
Explain any two of the following terms: Lethal gene Recessive gene Sex-linked gene. Suggest reasons why the fruit fly (Drosophila) is a suitable subject for genetic... show full transcript
Worked Solution & Example Answer:Explain any two of the following terms: Lethal gene Recessive gene Sex-linked gene - Leaving Cert Agricultural Science - Question 7 - 2009
Step 1
Explain any two of the following terms: Lethal gene
Answer
A lethal gene is one that, when expressed in the phenotype, can lead to the death of the organism. This type of gene disrupts vital biological processes, leading to reduced viability.
Another gene type is a recessive gene, which only manifests in the phenotype when an individual has two copies of this gene, one inherited from each parent. It is masked by a dominant gene in heterozygous situations.
Step 2
Suggest reasons why the fruit fly (Drosophila) is a suitable subject for genetics experiments.
Answer
Drosophila is an ideal subject for genetics experiments due to several factors:
- Short Lifespan: They have a rapid generation time, allowing for the observation of multiple generations in a short period.
- Large Offspring: Each mating can produce a large number of offspring, providing ample data for analysis.
- Simple Genetic Makeup: They have only four pairs of chromosomes, making genetic tracking less complex.
- Easily Observable Traits: Drosophila exhibits clear phenotypic traits, facilitating easy observation and experimentation.
Step 3
Show by means of suitable crosses how this result might occur starting with homozygous parents.
Answer
Starting with homozygous parents, we can denote:
- Green parents as GG (homozygous dominant)
- Albino parents as gg (homozygous recessive)
When crossing GG with gg:
- The F1 generation will all be Gg (green).
Now crossing Gg with Gg for the F2 generation, we can use a Punnett Square:
G g
----------------
G | GG | Gg |
----------------
g | Gg | gg |
----------------
- The genotypes of the F2 offspring will be:
- 1 GG (green)
- 2 Gg (green)
- 1 gg (albino)
Result:
- 3 Green (GG and Gg combined) to 1 Albino (gg).
Step 4
Briefly outline the principal stages of embryo transfer in cows.
Answer
The principal stages of embryo transfer in cows include:
- Hormonal Stimulation: The cow is injected with hormones (PMS) to stimulate superovulation, leading to the production of multiple eggs.
- Artificial Insemination: The cow is then mated with a top-class bull via artificial insemination to fertilize the eggs.
- Embryo Collection: After successful fertilization, embryos are flushed out and collected from the uterus.
- Embryo Transfer: Finally, the collected embryos are implanted into recipient cows, which are prepared to carry them to term and deliver calves.