In tomatoes, tall(D) is dominant over dwarf (d) and smooth fruit(P) is dominant over pubescent fruit (p), which is covered with fine hairs. A farmer has two tall and smooth tomato plants, which we will call plant A and plant B. The farmer crosses plants A and B with the same dwarf and pubescent plant and obtains the following numbers of progeny:
Plant A Plant B
DdPp 122 2
Ddpp 6 82
ddPp 4 82
ddpp 124 4
a) what are genotypes of Plant A and B
b) are loci that determine the height of the plant and pubsescene linked? if so, whats the percent recombination?
c) explain the diff. proportions of progeny
So for (a) I figured that both A and B's genotypes would be DdPp, because when looking at the genotypes given its impossible I think for either of them to be DD or PP because then those genotypes would show up.
For (b) I said they were linked because they may have been assorted independently, causing there to be 50% recombinant progeny. And so for part (c) I figured since its independently assorted, it may explain why the progeny's are practically flip flopped.
Please help and tell me if I did this correctly or what i did wrong. Thanks!
thanks bro !
a) Based on the information provided, we can determine the genotypes of Plant A and B by analyzing the progeny outcomes. Both Plant A and B produce the same genotype distribution in the progeny, which consists of four possible combinations: DdPp, Ddpp, ddPp, and ddpp.
Since both Plant A and B yield progeny with the genotype ddPp (which is present in both homozygous recessive combinations: ddpp and ddPp), we can determine that Plant A and B must be heterozygous for the genes that determine plant height (Dd) and fruit texture (Pp). Therefore, the genotypes of Plant A and B are DdPp.
b) To determine if the loci that determine plant height and pubescence are linked, we need to calculate the percent recombination. Recombination refers to the shuffling of genetic material during the process of meiosis, resulting in a different arrangement of alleles on chromosomes.
To calculate the percent recombination, we need to compare the number of recombinant progeny (those that do not match the genotypes of either parent) to the total number of progeny.
Progeny with genotypes:
- DdPp: 122 (Plant A) + 2 (Plant B) = 124
- Ddpp: 6 (Plant A) + 82 (Plant B) = 88
- ddPp: 4 (Plant A) + 82 (Plant B) = 86
- ddpp: 124 (Plant A) + 4 (Plant B) = 128
Total progeny= 124 + 88 + 86 + 128 = 426
The recombinant progeny are the ones with genotypes Ddpp and ddPp, which have frequencies of 88 and 86, respectively.
Recombination rate = (88 + 86) / 426 * 100 ≈ 40.1%
Since the recombination rate is not equal to 50%, we can conclude that the loci determining plant height and pubescence are linked.
c) The different proportions of progeny can be explained by the principles of Mendelian genetics and the laws of segregation and independent assortment.
The observed distribution of progeny suggests that the genes for plant height and fruit texture are inherited together most of the time (linked), as the recombinant progeny (Ddpp and ddPp) are present in significantly lower numbers compared to the non-recombinant progeny (DdPp and ddpp). This indicates that there is a higher chance that the alleles for these traits remain together during meiosis and crossover events.
Additionally, the different proportions of progeny may also arise due to chance variation, mutation, or other genetic factors that are not explicitly described in the given information.
Let's go through each part of the question to see if your answers are correct:
(a) The genotypes of Plant A and Plant B can be determined by analyzing the progeny. Let's look at the first row of numbers:
DdPp 122 2
From this data, we see that Plant A crossed with the dwarf and pubescent plant (genotype ddpp) produces 122 progeny with the genotype DdPp. This means that Plant A must have the genotype DdPp. Now let's look at the second row of numbers:
Ddpp 6 82
From this data, we see that Plant A crossed with the dwarf and pubescent plant (genotype ddpp) produces 6 progeny with the genotype Ddpp. This means that Plant A must carry the recessive allele for the fruit texture gene, which is p.
Based on the same reasoning, we can determine the genotype of Plant B. From the first row of numbers, we see that Plant B crossed with the dwarf and pubescent plant (genotype ddpp) produces 2 progeny with the genotype DdPp. This means that Plant B must carry the recessive allele for the height gene, which is d.
Therefore, the genotypes of Plant A and Plant B are DdPp and DdpP, respectively.
(b) To determine if the loci that determine height and pubescence are linked, we need to analyze if there is any recombination happening between these two traits. Recombination occurs when there is a shuffling of genetic material during meiosis.
To calculate the percent recombination, we need to look at the four possible combinations of alleles for the two loci: DP, Dp, dP, and dp. We can use the data given to calculate the recombination frequency.
From the data, we see that out of a total of 228 progeny from Plant A, 122 have the genotype DdPp. This means that 106 progeny have either the genotype Ddpp or ddPp.
Similarly, out of a total of 170 progeny from Plant B, 82 have the genotype DdPp. This means that 88 progeny have either the genotype Ddpp or ddPp.
Now let's calculate the recombination frequency using the formula:
Recombination frequency = (Number of recombinant progeny / Total number of progeny) * 100
From our calculations:
For Plant A: Recombinant progeny = 106, Total progeny = 228
For Plant B: Recombinant progeny = 88, Total progeny = 170
Recombination frequency for Plant A = (106 / 228) * 100 = 46.49%
Recombination frequency for Plant B = (88 / 170) * 100 = 51.76%
Since the recombination frequency is greater than 50% for both Plant A and Plant B, we can conclude that the loci determining height and pubescence are not linked.
(c) The differing proportions of progeny can be explained by the principles of Mendelian genetics. Each parent contributes one allele for each gene to their offspring. In this case, Plant A and Plant B are both heterozygous for the height and fruit texture genes (DdPp and DdpP, respectively).
When the two plants are crossed with the dwarf and pubescent plant (ddpp), the resulting progeny can have different combinations of alleles. The specific ratios of each genotype can be determined by applying Punnett square analysis.
The observed progeny numbers indicate that the dominant tall trait (D) and smooth fruit trait (P) are expressed more frequently than the recessive dwarf trait (d) and pubescent fruit trait (p). This is consistent with the principles of dominance and segregation, as described by Mendel.
It is important to note that while the proportions of progeny differ between Plant A and Plant B, the overall genetic ratio remains consistent with the expected Mendelian ratios based on the allele combinations of the parents.
In summary, your answer for (a) is correct. For (b), you correctly identified that the loci determining height and pubescence are not linked, but your reasoning for the 50% recombination is not accurate. And for (c), your explanation regarding the principles of Mendelian genetics is correct.