IPA kelas 9 : Pewarisan Sifat II (Persilangan Monohibrid : Hukum 1 Mendel)

Summary

This video lesson explains the principles of genetic inheritance, focusing on Mendel's laws. It introduces Mendel's work with pea plants, highlighting traits like flower and pod colors, and how they are passed from one generation to the next. Key genetic concepts such as dominant and recessive genes, alleles, genotype, phenotype, and gametes are explored. The lesson further discusses monohybrid crosses, both dominant and intermediate, and how genetic traits can be inherited and expressed in offspring. The video concludes with a preview of future lessons on more complex genetic crosses.

Takeaways

• 😀 Gregor Mendel is considered the father of genetics for his work on inheritance using pea plants.
• 😀 Mendel's experiments focused on traits like flower color and seed shape, with pea plants chosen due to their ability to self-pollinate and produce varied offspring.
• 😀 Mendel's laws of inheritance explain how traits are passed from parents to offspring through genes, which are carried on chromosomes.
• 😀 Dominant genes are represented by capital letters (e.g., 'A') and express stronger traits, while recessive genes are represented by lowercase letters (e.g., 'a') and are masked by dominant genes.
• 😀 Alleles are different forms of a gene, and an individual inherits one allele from each parent for a specific trait.
• 😀 Genotype refers to the genetic makeup of an organism (e.g., 'AA' or 'Aa'), while phenotype refers to the observable traits (e.g., flower color).
• 😀 A homozygous dominant genotype (e.g., 'AA') expresses the dominant trait, while a homozygous recessive genotype (e.g., 'aa') expresses the recessive trait.
• 😀 A heterozygous genotype (e.g., 'Aa') will express the dominant phenotype, as the dominant allele masks the recessive one.
• 😀 In Mendel's monohybrid crosses, the F1 generation of dominant and recessive traits results in a 3:1 phenotype ratio, with dominant traits appearing more frequently.
• 😀 In intermediate inheritance (also known as incomplete dominance), the offspring display a blend of both parental traits, as seen in the example of red and white flowers producing pink flowers.

Q & A

What is Mendel's law of inheritance?

Mendel's law of inheritance explains how traits are passed from parents to offspring. It is based on the observation of genetic patterns in pea plants, particularly the inheritance of dominant and recessive traits.

Why did Mendel choose pea plants for his genetic experiments?

Mendel chose pea plants (Pisum sativum) because they have easily observable traits, such as flower color and pod shape, they can self-pollinate or cross-pollinate, and they grow quickly, allowing for efficient observation of inheritance patterns.

What are dominant and recessive genes?

Dominant genes are those that express their traits when present, whereas recessive genes require two copies (homozygous) to express their traits. For example, a dominant gene for purple flowers will express the purple color even if only one copy is present.

What does the term 'allele' refer to?

An allele is a variant form of a gene. Each gene has two alleles, one inherited from each parent. Alleles can be dominant (represented by capital letters) or recessive (represented by lowercase letters).

What is the difference between genotype and phenotype?

Genotype refers to the genetic makeup of an individual, consisting of the alleles inherited from both parents. Phenotype refers to the observable traits or characteristics, such as flower color or plant height, resulting from the genotype.

What is the law of segregation?

The law of segregation, one of Mendel's laws, states that alleles for a given trait segregate, or separate, during the formation of gametes (egg and sperm). This means each gamete carries only one allele for each trait.

What is the significance of homozygous and heterozygous genotypes?

A homozygous genotype has two identical alleles for a trait (e.g., BB or bb), while a heterozygous genotype has two different alleles (e.g., Bb). Homozygous dominant alleles express the dominant trait, while heterozygous genotypes typically show the dominant trait.

How are monohybrid and dihybrid crosses different?

A monohybrid cross involves the inheritance of a single trait, whereas a dihybrid cross examines the inheritance of two traits simultaneously. The Punnett square for a dihybrid cross is more complex, showing the potential combinations of both traits.

What happens in an intermediate inheritance (or incomplete dominance) cross?

In intermediate inheritance, also known as incomplete dominance, the offspring exhibit a blending of the traits from the parents. For example, crossing red and white flowers may produce pink flowers, a blend of the two colors.

Can you explain the ratio of genotypes and phenotypes in a typical Mendelian monohybrid cross?

In a typical monohybrid cross where one trait is dominant (e.g., purple flowers), the F1 generation will show a 3:1 phenotypic ratio, with three plants exhibiting the dominant trait (purple flowers) and one exhibiting the recessive trait (white flowers). The genotypic ratio will be 1:2:1, with one homozygous dominant, two heterozygous, and one homozygous recessive.