Biology 9 Lesson 4: Crossing two pairs of traits
1. Theoretical Summary
1.1. Mendel’s experiment
– Perform experiments
– The test subject is still peas
– Menden crossed two types of purebred peas that differed in two pairs of contrasting traits: yellow seeds, smooth with green, wrinkled
– Analyze results of Mendel’s crosses based on phenotypic results in crosses
– From the result of the hybridization:
⇒ Ratio of gold: green: 3: 1; Smooth: wrinkle ratio: 3:1
Phenotypic ratio in F2: 9 yellow-smooth: 3 yellow- wrinkled: 3 green-smooth: 1 green- wrinkled
⇒ 9: 3: 3:1
– Conclusion: Through hybridization we see
- Phenotypic segregation ratio in F2 of each trait pair is 3: 1 according to the law of segregation.
- Phenotypic ratio in F2 is equal to the product of the ratio of the pairs of traits that make up it ⇒ The traits segregate independently.
1.2. Combinatorial Variation
– Observing the experiment, we found:
- In F2, in addition to the parental-like phenotypes in P which are yellow, smooth and wrinkled green.
- The appearance of other traits such as green, smooth and wrinkled yellow is called combined variation.
- Causes of combinatorial variation: it is the independent segregation of pairs of traits of P that gives rise to phenotypes other than P, this phenotype is called combinatorial variation.
Combinational variation is the appearance of phenotypes different from the parents due to a random combination of independently segregated traits.
– Meaning: genetic enrichment in organisms that have a form of sexual reproduction (mating).
2. Illustrated exercise
2.1. Type 1: Some problems related to the experiment of two pairs of traits and combinatorial variation
Question 1: Independent inheritance of contrasting pairs of traits produces combinatorial variation
A. only appears in Ffirst B. only appears in F2.
C. appears in both Ffirst both F2. D. never appears in Ffirst.
– Independent inheritance of pairs of contrasting traits produces combinatorial variation that occurs in both Ffirst both F2.
Verse 2: On what basis did Mendel assume that the color and shape of the peas in his experiments were inherited independently of each other?
– The reason why the color and shape of the peas in Mendel’s experiment were inherited independently of each other because the phenotypic ratio in F2 by the product of the ratios of its constituent traits.
– Customer F ratio2:
(yellow, smooth) x (green, wrinkled) = (yellow x green) x (smooth x wrinkled)
= (3:1) x (3:1) = 9: 3: 3: 1
2.2. Form 2: Applying the experiment of two pairs of traits to explain some phenomenological results.
Question 1: The essence of independent inheritance of traits is F2 necessarily have:
a) The rate of segregation of each pair of 3 dominant: 1 recessive.
b) The ratio of each phenotype is the product of the proportions of its constituent traits.
c) Four different phenotypes.
d) Combinational variations.
– The essence of independent inheritance of traits is F2 necessarily the ratio of each phenotype is equal to the product of the proportions of its constituent traits.
⇒ Choose B.
3.1. Essay exercises
Question 1: What is combinatorial variation? With what form of reproduction does it appear?
Verse 2: Following Mendel’s experiment, when crossing purebred peas with yellow, smooth seeds and green seeds, wrinkled together, Ffirst smooth, golden grain. When giving Ffirst self-pollination then F2 What is the phenotypic ratio?
Question 3: Why does combinatorial variation occur only in sexual reproduction?
Question 4: In Mendel’s two-pair crossbreeding experiment, when Ffirst What will be the results obtained in terms of phenotype?
3.2. Multiple choice exercises
Question 1: In Mendel’s two pairs of seed color and seed coat traits, the result in F2 have the lowest proportion of phenotypes:
A. Golden seed, smooth shell
B. Yellow seed, wrinkled shell
C. Green seeds, smooth skin
D. Green seeds, wrinkled shell
Verse 2: In Mendel’s two-pair cross in pea plants, when analyzing each pair of traits, F2 The ratio of each pair of traits is:
A. 9: 3: 3 :1
B. 3: 1
D. 1: 1: 1: 1
Question 3: The following genotypes are considered purebred:
D. All three genotypes mentioned above
Question 4: The following genotypes produce one type of gamete:
Question 5: The types of gametes that can be produced from genotype AaBb are:
A. AB, Ab, aB, ab
B. AB, Ab
C. Ab, aB, ab
D. AB, Ab, aB
Through the knowledge of the lesson Crossing two pairs of traits, students need to be able to perform the following knowledge:
– State the experiment of crossing two pairs of Mendel’s traits and draw comments.
– Identify the combinatorial variation that occurs in Mendel’s two pairs of traits.
– State the concept of combinatorial variation, give examples.