Answer:
- a ratio of 50% parental type, 50% recombinant type
- that each genotypic class of gametes makes up 25%
Step-by-step explanation:
Available data:
- Two genes assort independently
- A double heterozygote produces gametes.
Options:
- a ratio of 30% parental type, 70% recombinant type
- a ratio of 50% parental type, 50% recombinant type
- a ratio of 60% parental type, 40% recombinant type
- that each genotypic class of gametes makes up 50%
- that each genotypic class of gametes makes up 25%
To select the statements that apply, we need to remember what happens in meiosis.
During metaphase I, homologous pairs migrate to the equatorial plane, where they randomly aline with their kinetochores facing opposite poles. The random arrangement of tetrads is different in every cell going through the meiosis process. There is no equal alinement between two cells. When tetrads aline in the equatorial plane, there is no predetermined order for each of the homologous chromosomes of each tetrad to face one of the poles and then migrate to it while separating. Any chromosome of the homologous pair might point to any of the cell poles and then migrate to it. Each of the chromosomes has two possibilities for orientation at the plane. When the new haploid cells form during Meiosis II, the number of variations in each of the cells is also different and depends on the chromosomes that form that cell. This random order in the equatorial plane is what introduces variation into the gametes. It is almost impossible that gametes resulting from meiosis will get the same genetic charge. The random combination of chromosomes during gametogenesis produces a parental type of gametes in the same proportion as recombinant gametes.
We should also keep in mind that genes that express 50% of recombination frequency or more are not linked genes. If they show less than 50% of recombination frequency, then we are talking about linked genes, and the proportions or percentages of the gametes produced through meiosis will be different than 50:50
Let us say, for instance, that the dihybrid is LlGg
Each individual will produce four gametes:
- LG Parental (25%)
- lg Parental (25%)
- Lg Recombinant (25%)
- lG Recombinant (25%)
Each of the gametes has 25% probability of occurrence because genes are not linked. They assort independently.