Question

name class date review questions 1. describe mendels first experiment. 2. pure - bred plants are called the generation and the offspring of a cross between pure - bred parents is called the generation. 3. the trait is the trait that appears when it is present and the trait is the trait that doesnt appear if the dominant trait is present. 4. name two traits that are dominant in humans. 5. in a cross of a black and white guinea pigs, all the offspring produced were black. what was the dominant trait? what was the recessive trait?

Explanation:

1. Mendel's first experiment: Gregor Mendel's first experiment involved monohybrid crosses with pea plants. He cross - pollinated pure - bred (homozygous) pea plants that differed in one trait (e.g., tall vs. short). For example, he took pure - bred tall pea plants and pure - bred short pea plants and crossed them. The pure - bred plants are the parental (P) generation. The offspring of this cross are the first filial (F₁) generation. In his first experiment, when he crossed pure - bred tall and short plants, all the F₁ offspring were tall. Then, he allowed the F₁ plants to self - pollinate, and in the F₂ generation, the ratio of tall to short plants was approximately 3:1.
2. Generations of pure - bred and cross - offspring: Pure - bred plants are called the P (parental) generation. When pure - bred parents are crossed, their offspring are called the F₁ (first filial) generation. This is a fundamental concept in Mendelian genetics, where the P generation is the starting set of pure - bred individuals, and the F₁ is the first generation of offspring from the cross of P generation individuals.
3. Dominant and recessive traits: The dominant trait is the trait that appears when it is present in the genotype (even if it's in a heterozygous state, i.e., with one dominant and one recessive allele). The recessive trait is the trait that is masked or doesn't appear when the dominant trait is present (it only appears when two recessive alleles are present, in a homozygous recessive genotype). For example, in pea plants, the tall trait is dominant and the short trait is recessive. If a plant has a dominant allele for tallness, it will be tall, and the short trait (recessive) will only be expressed if the plant has two recessive alleles.
4. Dominant traits in humans: Two dominant traits in humans are:

• Widow's peak: The allele for having a widow's peak (a V - shaped hairline at the forehead) is dominant. If a person has at least one dominant allele for this trait, they will have a widow's peak.
• Free earlobes: The allele for free earlobes (earlobes that hang freely, not attached directly to the side of the head) is dominant. A person with at least one dominant allele for this trait will have free earlobes.

1. Dominant and recessive traits in guinea pigs cross: In a cross between a black and a white guinea pig, if all the offspring are black, this means that the black trait is dominant and the white trait is recessive. This is because the dominant trait is the one that is expressed in the offspring when one parent has the dominant allele and the other has the recessive allele. So, the dominant trait is black and the recessive trait is white. When the black (dominant) - allele - carrying guinea pig is crossed with the white (recessive) - allele - carrying guinea pig, the dominant allele masks the recessive allele in the offspring, resulting in all black offspring.

Answer:

1. Mendel's first experiment: Crossed pure - bred pea plants differing in one trait (e.g., tall/short). P generation (pure - bred) cross gave F₁ (all tall for tall×short). F₁ self - pollinated gave F₂ with ~ 3:1 tall:short ratio.
2. Pure - bred: P (parental); Offspring of cross: F₁ (first filial)
3. Dominant; Recessive
4. Widow's peak, Free earlobes (other examples: dark hair, curly hair, etc. are also acceptable as long as they are dominant in humans)
5. Dominant trait: Black; Recessive trait: White