POLA-POLA HEREDITAS part 3 (PENYIMPANGAN SEMU HUKUM MENDEL-interaksi antaralel)| Biologi XII SMA

Summary

This video explains the concept of 'pseudo deviations' from Mendel's laws of inheritance, where certain genetic patterns do not follow the expected Mendelian ratios. It covers incomplete dominance, where the dominant allele doesn’t fully mask the recessive allele, and codominance, where both alleles are expressed equally. The video also addresses lethal alleles, which cause death in specific genetic combinations, and multiple alleles, where more than two allele forms influence traits. Through examples involving snapdragon flowers, cattle, corn, and rabbits, the video showcases the complexity and variety in genetic inheritance beyond Mendel’s original laws.

Takeaways

• 😀 Incomplete dominance occurs when neither allele completely dominates the other, leading to a blended phenotype, as seen in Snapdragon flowers.
• 😀 Incomplete dominance results in a 1:2:1 phenotypic ratio in the F2 generation, instead of the usual 3:1 ratio seen in Mendelian inheritance.
• 😀 Codominance is when both alleles express equally and independently, without affecting each other, as demonstrated by Roan cattle with both red and white hair.
• 😀 In codominance, the F2 generation shows a 1:2:1 phenotypic ratio, with red, roan, and white phenotypes.
• 😀 Lethal alleles can cause death when inherited in the homozygous state, either dominant or recessive.
• 😀 Recessive lethal alleles, like in albino corn, cause death in homozygous recessive individuals.
• 😀 Dominant lethal alleles can cause death in homozygous dominant individuals, as seen in polydactylism in humans.
• 😀 Multiple alleles exist for certain traits, providing more complex inheritance patterns, such as in human blood groups and rabbit fur color.
• 😀 Human blood types are determined by three alleles (IA, IB, and i), with IA and IB being codominant and i being recessive.
• 😀 The inheritance of rabbit fur color is controlled by four alleles (C, cch, ch, c), where different combinations result in full color, chinchilla, Himalayan, or albino fur.
• 😀 These genetic deviations (incomplete dominance, codominance, lethal alleles, and multiple alleles) challenge Mendel's original laws but provide a richer understanding of inheritance.

Q & A

What are the two main causes of deviations from Mendel's laws of inheritance?

The two main causes of deviations from Mendel's laws are allele interactions and genetic interactions.

What is incomplete dominance and how does it differ from Mendel's first law?

Incomplete dominance occurs when the dominant allele does not fully mask the recessive allele, resulting in a phenotype that is a blend of both traits. This contrasts with Mendel's first law, where the dominant allele completely masks the recessive allele in the heterozygous condition.

Can you explain the genetic outcome of the Snapdragon flower example in incomplete dominance?

In the Snapdragon example, red flowers (homozygous dominant) are crossed with white flowers (homozygous recessive). The resulting offspring are all heterozygous, producing a phenotype of pink flowers, which is a blend of red and white.

What is codominance, and how does it work in the example of Roan cows?

Codominance occurs when two alleles of a gene are equally dominant and both are expressed in the phenotype. In the case of Roan cows, a red (Er^B) and white (Er^W) cow are crossed, producing offspring with both red and white hairs, resulting in a 'Roan' coat, where both alleles are visibly expressed.

What are lethal alleles, and how do they affect genetic inheritance?

Lethal alleles are alleles that cause death when present in a homozygous condition. There are both dominant and recessive lethal alleles. For example, in corn, the homozygous recessive allele for albino corn causes the plant to die, while in chickens, a dominant allele causes death when homozygous.

How does the inheritance of lethal alleles manifest in corn plants?

In corn, the homozygous recessive genotype for albino corn (g^g) is lethal, meaning that plants with this genotype die. The heterozygous green corn (Gg) survives and is green, while homozygous dominant (GG) also results in green plants.

What are multiple alleles, and how do they influence blood type inheritance in humans?

Multiple alleles refer to a gene that has more than two possible alleles. In humans, blood type is determined by three alleles: I^A, I^B, and i. Both I^A and I^B are codominant to each other, while both are dominant over the i allele. The combinations of these alleles determine the four main blood types: A, B, AB, and O.

How does the inheritance of blood type ABO work in humans?

In the ABO blood group system, individuals inherit one allele from each parent. The I^A and I^B alleles are codominant, so when both are inherited, the blood type will be AB. The i allele is recessive, so individuals with blood type O must inherit two i alleles.

Can you explain the inheritance pattern for fur color in rabbits with multiple alleles?

In rabbits, fur color is influenced by four alleles: C^B (black), C^H (Himalayan), c^ch (chinchilla), and c (albino). These alleles have a dominance hierarchy, with C^B being the most dominant and c being recessive. The interaction of these alleles leads to a variety of fur colors, including black, chinchilla, Himalayan, and albino.

What is the phenotypic ratio in the second generation (F2) for incomplete dominance in Snapdragon flowers?

In the second generation (F2) of Snapdragon flowers, the phenotypic ratio is 1:2:1. This means one-quarter of the offspring will have red flowers, half will have pink flowers (heterozygous), and one-quarter will have white flowers.