Dihybrid cross
When crossing two heterozygous red flowers (Rr), you would use a Punnett square to determine the possible genotypes and phenotypes of the offspring. In this case, the genotypes of the parents are Rr x Rr. The possible offspring genotypes would be RR, Rr, and rr, with a phenotypic ratio of 1 red : 2 pink : 1 white flower.
Make two punnett squares- one for Yy x YY and one for rr x RR the possible outcomes for Yy x YY are: YY Yy the only outcome for rr x RR is Rr. so the gametes of the two could be either YY Rr or Yy Rr
A monohybrid cross is a cross between two individuals that are homozygous for different alleles of the same gene. An example is a cross between a red-eyed (RR) fruit fly and a white-eyed (WW) fruitfly.
In a BB x bb cross, all offspring will have the genotype Bb. The offspring will exhibit the dominant trait of the B allele.
In general, pink flowers tend to be an example of incomplete dominance of the gene for red flowers. Therefore, the phenotypic ratio of a cross between two pink flowers would be the same as the genotypic ratio of 1:2:1. In other words, 1 red to 2 pink to 1 white.
The cross would result In 50% pink and 50% white.
The cross RR X Dd is showing two different genes for the parents (it is showing RR for one parent and Dd for the other) - therefore this is not a dihybrid cross. However, if it was RRDd X RRDd, this would be a dihybrid cross. For a dihybrid cross, you need to include two different genes (and show these genes in both the parents). So - BbFf X bbff, GGTT X ggtt, KKPp X KkPp - are all examples of dihybrid crosses.
To figure this out, use a Punnet Square.First, set up a test cross, like this:Rr x rrThis shows what you are crossing. Now you can make a Punnet Square.R rr Rr rr There is a 50/50 chance that the corn plant will have thegenotype rr.r Rr rr
Lets start with using letters to symbolize each allele of each parent: Roan Bull x White Cow --> Rr x rr (where the alleles R = red and r = white). The resulting ratio of offspring is the following: Rr = 50% rr = 50% RR = 0% Since there are too many little "r"'s and not enough big "R"'s, we can only get a cross of white and roan calves to a ratio of 1:1. Red calves do not exist in this cross.
A test cross would involve crossing a pea plant with a constricted pod (to determine its genotype) with a homozygous recessive plant (constricted pod), as this cross would reveal whether the first plant is heterozygous or homozygous dominant for the trait of pod shape.
Let's say we're talking about red flowers (red=dominant, R allele) vs white flowers (white=recessive, r allele) If you cross two homozygous red flowers, RR x RR, you can only get RR offspring, or all red flowers. RR=genotype (what alleles, or genes, they have), red=phenotype (what they look like) To make the Punnett square, draw a 4-box diagram on a piece of paper by drawing a diagonal line and then a horizontal line halfway down so you get 4 squares. On the top of the box, put R R and along the left side, put R and then another R under it. To fill in the boxes for the Punnett square, cross the top left-hand gene (R) with the top gene on the left-hand side. You'll get RR. Do the same for the top right-hand gene (R) and the top gene on the side. You'll also get RR. Cross the bottom R with the left gene on the top (R) and the right gene on the top. All combinations will be RR in this example. If you had a red flower that had a homozygous genotype (RR) with a white flower, also homozygous (rr), the results are more interesting. When you draw your Punnett square, you'll see that you get one RR combination, two Rr combinations and one rr combination. This means that the F1 generation (offspring) will be: 25% homozygous red (RR) 50% heterozygous red (Rr) 25% homozygous white (rr) Put another way, you'll have one white flower and three red flowers, and two of those red flowers carry a gene for white which is not expressed because it is recessive.
If they are expressing the trait, 100%, as their genotypes would be, rr X rr If they both carry the trait and it is dominated, Rr X Rr, then the probability would be, 25% of their child expressing the trait.
When crossing two heterozygous red flowers (Rr), you would use a Punnett square to determine the possible genotypes and phenotypes of the offspring. In this case, the genotypes of the parents are Rr x Rr. The possible offspring genotypes would be RR, Rr, and rr, with a phenotypic ratio of 1 red : 2 pink : 1 white flower.
RR X rr 100% Rr Heterozygous resistant for poison ivy.
vt x rr
Over 18 Its rr
In genetics, you can either have a dominant allele (A) or a recessive allele (a). Being homozygous means that you have both of either a dominant or a recessive allele (ie you are either AA or aa). If the trait is a recessive trait, then you need to have it be homozygous recessive in order to express that trait. Hope this was helpful! :-)