1. Assume tall (T) is completely dominant to dwarf (t) in a...

1. Assume tall (T) is completely dominant to dwarf (t) in a certain species of plant. If a homozygous dominant individual is crossed with a homozygous dwarf. What will are the genotype and phenotype ratios of the offspring plants? 2. In pea plants Tall is dominant to short. A tall plant is mated with a short plant. a. What are the possible genotypes for the parent plants? (think carefully) b. How do we determine what the genotype of the tall plant is? c. You cross the tall and short parent plant and have 78 offspring plants; 35 are tall and 38 are short. What is the genotype of the tall plant? 3. Pea flowers may be purple (P) or white (p). Pea seeds may be round (R) or wrinkled (r). You do a dihybrid cross for these traits. Out of 1000 offspring, how many would you expect to have the following: a. White flowers and wrinkled seeds? b. Purple flowers and wrinkled seeds? c. White flowers and round seeds? d. Purple flowers and round seeds? e. How many would you expect to be homozygous dominant for both traits? (advanced question!) 4. If a heterozygous plant is allowed to self-pollinate, what proportion of the offspring will also be heterozygous?

Transcript

00:01 Hello students.

00:02 Today's question is about we know that t capital t is dominant to small t and homozygous dominant crossed with the homozygous dwarf.

00:11 So find the genotype and phenotype.

00:13 Find the genotype and phenotype.

00:16 So genotype of the homozygous.

00:20 Homosigus is homozygous if we talk about dominant tall.

00:25 It is tt and dwarf is tt, small t t t t t.

00:29 So this is this is for the tall and dwarf and if we cross them, if we cross them, we are going to have genotypic ratio.

00:38 So if we cross them like this, this is t -t and again t -t, again t -t, again t -t.

00:50 So this is the genotypic ratio.

00:54 So if we talk about t -t, so that is zero and hetero is one which indicates true hetero and small is also zero and talking about even if this is hetero but the phenotypic ratio is tall phenotypic is tall and doof are going to be zero doof are going to be zero so this is the correct for the first answer for the first answer they would be all hetero they will be all hetero and they would be tall now next is if tall mated with short how would we determine the genotype of parent and how would we determine the genotype of tall and genotype of tall so let's answer this question so a genotype of tall it can be either t t or it can be t and genotype of short plant is t t small t so for the genotype of the tall plant if we determine the genotype of tall plant, then obviously what we need to do, we have to test across it.

02:08 We have to test cross that tall plant with the short plant, tall plant with short plant which is t -t, which is a small t -t.

02:22 Now next is, so if tall plant is t -t and small plant is t -t, it is going to result like this.

02:31 It is going to result like this as the a verb.

02:36 So if the genotype of tall plant is t -t, if genotype of tall plant is t -t, all the progenies will be t -t.

02:45 So they all will be tall.

02:47 All will be tall.

02:50 So let's take the look at the another answer.

02:54 So it is purple and round.

02:59 Purple or white so purple is for p and this is for small p and round is r and wrinkled for small r out of thousand how many would you expect to have the following white and wrinkled purple and wrinkled white and so to determine the to determine the genotype of tall we can see that tall can be having t t t t so any of them can be the genotype of tall because tall can be homozygeneal dominant and hetero and hetero so next is about out of the thousand how many would you expect to following white and wrinkled purple and wrinkled white and round purple and round homozygous is dominant for both trades so it is having both the trades now we are counting both the trades so we know that this is a dihybrid ratio this is for the dihybrid ratio and it becomes it is nine three three one so di hybrid ratio in a normal normally when we consider two traits, the dihybrid ratio is 9331...

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