Yellow peas (Y) are dominant over green peas (y) and round peas (R) are dominant over wrinkled peas (r). Complete the dihybrid cross if two peas are crossed.
To complete the dihybrid cross, we need to determine the possible genotypes and phenotypes of the offspring.
Let's represent one parent as YyRr, where Yy represents yellow peas and Rr represents round peas.
The possible gametes the parent can produce are:
- YR
- Yr
- yR
- yr
Now, let's represent the other parent as YyRr as well.
The possible gametes the second parent can produce are the same:
- YR
- Yr
- yR
- yr
To complete the dihybrid cross, we need to combine these possible gametes from each parent.
The Punnett square for this dihybrid cross would be:
| YR | Yr | yR | yr
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YR | YYRR | YYRr | YyRR | YyRr
----------------------------------------------------
Yr | YYRr | YYrr | YyRr | Yyrr
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yR | YyRR | YyRr | yyRR | yyRr
----------------------------------------------------
yr | YyRr | Yyrr | yyRr | yyrr
Now, let's determine the genotypes and phenotypes of the offspring:
YYRR - Yellow, round peas
YYRr - Yellow, round peas
YyRR - Yellow, round peas
YyRr - Yellow, round peas
YYRr - Yellow, round peas
YYrr - Yellow, wrinkled peas
YyRr - Yellow, round peas
Yyrr - Yellow, wrinkled peas
YyRR - Yellow, round peas
YyRr - Yellow, round peas
yyRR - Green, round peas
yyRr - Green, round peas
YyRr - Yellow, round peas
Yyrr - Yellow, wrinkled peas
yyRr - Green, round peas
yyrr - Green, wrinkled peas
So, the dihybrid cross predicts that the offspring will have yellow and green peas along with round and wrinkled peas in a ratio of 9:3:3:1.
To complete a dihybrid cross, we need to consider two different sets of alleles and their inheritance patterns. In this case, we have yellow (Y) dominance over green (y) peas and round (R) dominance over wrinkled (r) peas.
Let's take the parental genotype for the first parent as YR (yellow and round), and for the second parent as yyrr (green and wrinkled).
Step 1: Write down the alleles for both parents.
Parent 1: YR
Parent 2: yyrr
Step 2: Determine the possible gametes for each parent.
Parent 1's possible gametes: YR
Parent 2's possible gametes:
- For y alleles: y
- For r alleles: r
Step 3: Create a Punnett square by combining the possible gametes.
Remember to list the gametes for each parent along the top and side of the square.
Write the possible combinations of the alleles in the boxes inside the square.
| YR |
-------------------------------
yy | YyRr |
yy | YyRr |
rr | YyRr |
rr | YyRr |
Step 4: Analyze the genotypes and phenotypes of the offspring.
From the Punnett square, we can see that there are 16 possible combinations in the offspring (4 boxes multiplied by 4 boxes). Let's break them down:
- Out of the 16 offspring, 9 have the dominant yellow pea phenotype (Y_) and 7 have the recessive green pea phenotype (yy).
- Additionally, 12 have the dominant round pea phenotype (_R) and 4 have the recessive wrinkled pea phenotype (rr).
Therefore, the genotypic ratio is 9 Y_R_ : 7 yyR_ : 4 Y_rr : 1 yyrr.
The phenotypic ratio is 9 yellow and round peas : 7 green and round peas : 4 yellow and wrinkled peas : 1 green and wrinkled pea.
To complete a dihybrid cross, we need to determine the possible genotypes of the parent peas and then determine the genotype and phenotype possibilities of the offspring.
Let's denote the dominant yellow pea allele as Y and the recessive green pea allele as y. Similarly, let's denote the dominant round pea allele as R and the recessive wrinkled pea allele as r.
If we have two peas crossed, we need to determine the genotypes of the parents. Let's say one parent has the genotype YyRr, and the other parent has the genotype YYRR.
To determine the possible genotypes of the offspring, we can use the FOIL method:
F - First letters: Y from the first parent, Y from the second parent. The genotype possibilities are YY.
O - Outer letters: Y from the first parent, R from the second parent. The genotype possibilities are YR.
I - Inner letters: y from the first parent, R from the second parent. The genotype possibilities are yR.
L - Last letters: y from the first parent, R from the second parent. The genotype possibilities are yr.
Therefore, the possible genotypes of the offspring are YY, YR, yR, and yr.
To determine the possible phenotypes, we can refer to the dominance relationships stated earlier. Yellow (Y) is dominant over green (y), and round (R) is dominant over wrinkled (r). Therefore, the possible phenotypes of the offspring are yellow and round (YYRR), yellow and wrinkled (YYRr), yellow and round (YYrr), yellow and round (YyRR), yellow and wrinkled (YyRr), yellow and round (Yyrr), green and round (yyRR), green and wrinkled (yyRr), and green and round (yyrr).
So, the dihybrid cross results in nine possible genotype-phenotype combinations for the offspring.