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Explain the following terms which are used in genetics: homozygous, recessive, phenotype - Leaving Cert Biology - Question 11 - 2008
Question 11
Explain the following terms which are used in genetics: homozygous, recessive, phenotype. In the fruit fly, Drosophila, the allele for grey body (G) is dominant to ... show full transcript
Worked Solution & Example Answer:Explain the following terms which are used in genetics: homozygous, recessive, phenotype - Leaving Cert Biology - Question 11 - 2008
Step 1
Explain the following terms which are used in genetics: homozygous, recessive, phenotype.
Answer
Homozygous refers to an organism that has identical alleles for a particular trait. This means both inherited genes from each parent are the same.
Recessive describes an allele whose expression is masked by a dominant allele. An organism must have two copies of the recessive allele for it to express the trait associated with it.
Phenotype is the physical appearance or expression of a genotype, influenced by both genetic factors and environmental factors.
Step 2
Determine all the possible genotypes and phenotypes of the progeny of the following cross: grey body, long wings (heterozygous for both) X ebony body, vestigial wings.
Answer
For the cross between a heterozygous grey body, long wings (GgLl) and an ebony body, vestigial wings (ggll), we can use a Punnett square to determine the genotypes:
- Possible gametes from grey body, long wings: GL, Gl, gL, gl.
- Possible gametes from ebony body, vestigial wings: gl, gl, gl, gl.
Using these gametes, the potential offspring genotypes include:
- GgLl (grey body, long wings)
- Ggll (grey body, vestigial wings)
- ggLl (ebony body, long wings)
- ggl (ebony body, vestigial wings)
The resulting phenotypes are:
- Grey body, long wings
- Grey body, vestigial wings
- Ebony body, long wings
- Ebony body, vestigial wings.
Step 3
What is the significance of the fact that the two allele pairs are located on different chromosome pairs?
Answer
The significance of the two allele pairs being located on different chromosome pairs is that they assort independently during gamete formation. This independent assortment can lead to greater genetic variation in the offspring, as the alleles for different traits can combine in numerous ways.
Step 4
What is meant by sex-linked?
Answer
Sex-linked refers to genes that are located on the sex chromosomes. In humans, the X and Y chromosomes determine an individual's sex, and any genes located on these chromosomes can exhibit specific inheritance patterns that are different from autosomal (non-sex) genes.
Step 5
Determine the possible genotypes and phenotypes of the progeny of the following cross: haemophilic male X heterozygous normal female.
Answer
For the cross between a haemophilic male (X^nY) and a heterozygous normal female (X^NX^n), we can find the possible progeny:
The possible gametes from the haemophilic male: X^n and Y. The possible gametes from the normal female: X^N and X^n.
Potential offspring genotypes include:
- X^NX^n (normal carrier female)
- X^nX^n (haemophilic female)
- X^NY (normal male)
- X^nY (haemophilic male)
The resulting phenotypes will be:
- Normal carrier female
- Haemophilic female
- Normal male
- Haemophilic male.