Biology 9 Lesson 3: Cross a pair of traits
1. Theoretical Summary
1.1. Some concepts
Genotype: is the combination of all genes in an organism.
Homozygous: genotype contains the same pair of genes.
– Example: Homozygous dominant: AA; Co-diving: aa
Heterozygous: genotype contains different pairs of corresponding genes.
– Example: Heterozygous: Aa
1.2. Hybrid analysis
– Analytical cross is a cross between an individual with a dominant trait that needs to be genotyped with an individual with recessive trait.
– If the result of same-sex crossing, the individual with the dominant trait has the homozygous genotype.
– If the results of the cross are analyzed in a 1:1 ratio, then the individual with the dominant trait has the heterozygous genotype.
1.3. Reversible hybrid
– Reversible hybrid is a hybrid conducted in two different directions: In the first direction this form is used as the father, in the second direction it is used as the mother.
- Hybrid: Mother (AA) x Dad (aa)
- Cross-reverse: Mother(aa) x Father(AA)
– Use reversible crosses to determine traits that are determined by genes located on autosomes when the results of the reverse crosses are the same.
1.4. The meaning of the dominant-recessive correlation
– Dominant-recessive correlation is a common phenomenon in organisms, in which dominant traits are often beneficial. Therefore, in breeding, it is necessary to detect dominant traits in order to concentrate dominant genes in the same genotype to create varieties with economic value.
1.5. Incomplete dominance
– Incomplete dominance is the case when the dominant trait is not fully expressed, the F . hybridfirst intermediate between father and mother.
2. Illustrated exercise
2.1. Form 1: Factors and contents related to analytical hybridization and incomplete dominance
Question 1: How to determine the genotype of an individual with a dominant trait?
– To determine the genotype of the organism carrying the dominant trait, analytical crosses should be performed. An analytical cross is a cross between an individual with a dominant trait that needs to be genotyped with an individual with a recessive trait.
Verse 2: Compare complete dominance and incomplete dominance?
– Full dominance:
- Phenotype Ffirst (Aa): Phenotype of father or mother
- Phenotypic ratio in F2: 3 dominant, 1 recessive
- Analytical crosses are used in the following cases: Determine the genotype of an individual with a dominant trait
– Incomplete dominance:
- Phenotype Ffirst (Aa): Expression of an intermediate trait
- Phenotypic ratio in F2: 1 dominant: 2 intermediate: 1 recessive
- Analytical hybrids are used in the following cases: No need
2.2. Form 2: Applying analytic hybridization and incomplete dominant inheritance to solve some problems on the laws of heredity
Question 1: When the purebred red tomato plants are analyzed, we get:
a) All golden fruit
b) All red fruit
c) Ratio of 1 red: 1 yellow
d) Ratio of 3 reds: 1 yellow
Purebred red tomato plant with genotype AA
P: AA x aaa
Red fruit x Yellow fruit
GP: Ah ah
Ffirst: Aa (100%) Red fruit
Verse 2: In one species, the gene A for black hair is dominant over the gene a for white hair; The gene B for curly hair is dominant over the gene b for straight hair. These genes segregate independently of each other and are located on the autosome.
For purebred black, curly breed crossed with white, straight breed Ffirst. For Ffirst What will be the genotype and phenotype of the crossbreed?
P: Black, curly (AABB) x White, straight (aabb)
GP: AB ab
Ffirst: AaBb – black, curly hair
Pa: AaBb x aabb
Gpa: AB, Ab, aB, ab ab
Fa: 1 AaBb: 1 Aabb: 1 aaBb: 1 aabb
1 black, curly: 1 black, straight: 1 white, curly: 1 white, straight.
3.1. Essay exercises
Question 1: What is the significance of dominant-recessive contrast of traits in production?
Verse 2: In fruit flies, the V gene for long wings, V for penguins. Ffirst 50% of longwing flies: 50% of penguins. Continue to feed F . fliesfirst mating is in F2 Statistical results in the whole population have a ratio of 9 penguins: 7 longwing flies.
1. Argue and write a hybrid diagram from P to F2.
2. Want to determine the genotype of any longwing fly in F2 what must be performed?
3.2. Multiple choice exercises
Question 1: Indicates that a gene determines a trait and the B allele is dominant over the b allele. Theoretically, the cross Bb x Bb produces a child with
A. 2 types of genotypes, 2 types of phenotypes
B. 3 types of genotypes, 2 types of phenotypes
C. 2 types of genotypes, 3 types of phenotypes
D. 3 types of genotypes, 3 types of phenotypes
Verse 2: The result of crossing a trait pair in Mendel’s experiment gives the phenotypic ratio in F2 to be
A. 1 dominant: 1 recessive
B. 2 dominant: 1 recessive
C. 3 dominant: 1 recessive
D. 4 dominant: 1 recessive
Question 3: In dogs, short hair is dominant over long hair.
P: Non-pure shorthair X non-pure shorthair, results in Ffirst how?
A. All short hair
B. All long hair
C. 1 short hair: 1 long hair
D. 3 short hairs: 1 long hair
Question 4: When two red-flowered pea plants are cross-pollinated, Ffirst has a ratio of 3 red flowers: 1 white flower. What is the genotype of P?
A. P: AA x AA B. P: AA x Aa
C. P: Aa x AA D. P: Aa x Aa
Question 5: In peas, yellow seeds are dominant over green seeds. Crossing between purebred yellow-seeded plants and green-seeded plants obtained Ffirst. Tree Ffirst What is the phenotypic ratio?
A. 3 yellow beads: 1 green seed
B. 1 yellow seed: 1 green seed
C. 5 yellow seeds: 3 green seeds.
D. 100% gold beads.
After studying the lesson Lai a pair of these traits, you need:
– Identify the concepts: genotype, phenotype, homozygous, heterozygous…
– Explain the dominant-recessive correlation.
– State the meaning of analytical hybrids in life and production.
– Understand the mechanism of incomplete dominance.