PENYIMPANGAN SEMU HUKUM MENDEL (INTERAKSI ALEL) SMA KELAS 12/GENETIKA SMA KELAS 12/BIOLOGI KELAS 12

Summary

In this video, the concept of deviations from Mendel's laws of inheritance is explored, focusing on the impact of allele interactions. It discusses various genetic phenomena like incomplete dominance, codominance, multiple alleles, and lethal alleles, with examples such as Snapdragon flowers, blood group inheritance, and rabbit fur color. The video highlights how these interactions result in different phenotypic ratios, which deviate from the expected Mendelian ratios. The explanations provide insights into how these genetic patterns play out in real-world scenarios, enhancing the understanding of genetic inheritance beyond Mendel’s classical principles.

Takeaways

• 😀 Mendel's Law of Segregation states that alleles for a gene separate during gamete formation, leading to a 3:1 phenotypic ratio in a monohybrid cross.
• 😀 Mendel's Law of Independent Assortment asserts that genes for different traits assort independently, resulting in a 9:3:3:1 phenotypic ratio in a dihybrid cross.
• 😀 Deviations from Mendel’s laws can occur through allele interactions and gene interactions, altering typical phenotypic ratios.
• 😀 Incomplete dominance occurs when a dominant allele does not fully mask the recessive allele, resulting in an intermediate phenotype (e.g., pink flowers in Snapdragon).
• 😀 Codominance involves both alleles being expressed equally in a heterozygous individual, such as the AB blood type in humans.
• 😀 Multiple alleles can control a single trait, as seen in coat color inheritance in rabbits, with alleles for gray, chinchilla, Himalaya, and albino fur.
• 😀 Lethal alleles can cause death in homozygous individuals, such as in the case of Redup chickens or albino plants.
• 😀 Atavism refers to the reappearance of ancestral traits that were not expressed in recent generations.
• 😀 Polygenic inheritance involves multiple genes contributing to a single trait, leading to more complex phenotypic outcomes.
• 😀 Epistasis occurs when one gene masks the expression of another gene, which can be dominant-recessive, dominant-dominant, or recessive-recessive in nature.
• 😀 Genetic crosses, such as between red and white Snapdragon flowers or blood type inheritance, can demonstrate codominance, incomplete dominance, and multiple alleles, providing real-world examples of genetic principles.

Q & A

What is Mendel's Law of Segregation?

Mendel's Law of Segregation states that during the formation of gametes, the alleles for a gene separate so that each gamete carries only one allele for each gene.

How does Mendel's Law of Assortment apply in genetic inheritance?

Mendel's Law of Assortment states that genes located on different chromosomes assort independently of each other during gamete formation, leading to genetic variation.

What is incomplete dominance, and can you provide an example?

Incomplete dominance occurs when one allele is not completely dominant over another, resulting in an intermediate phenotype. An example is the Snapdragon flower, where crossing red and white flowers produces pink offspring.

What is codominance and how does it differ from incomplete dominance?

Codominance occurs when both alleles in a heterozygous individual are fully expressed, such as in blood group inheritance (A and B alleles produce AB blood type). Unlike incomplete dominance, where an intermediate phenotype appears, codominance shows both phenotypes equally.

What is meant by multiple alleles, and can you provide an example from animals?

Multiple alleles refer to the presence of more than two allele forms for a gene. An example is the fur color in rabbits, where there are multiple alleles (W for normal, Wch for chinchilla, WH for Himalaya, and w for albino).

Can you explain what lethal alleles are and provide an example?

Lethal alleles are alleles that cause death when present in certain genetic combinations. For example, in chickens, the Redep gene is a lethal dominant allele that leads to death in homozygous dominant individuals.

How do lethal dominant alleles differ from lethal recessive alleles?

Lethal dominant alleles cause death in the homozygous dominant state, while lethal recessive alleles only cause death in the homozygous recessive state.

What is epistasis, and how does it affect gene expression?

Epistasis occurs when one gene can mask or alter the expression of another gene. It can be dominant or recessive, affecting how traits are inherited and expressed.

How does polygenic inheritance differ from Mendelian inheritance?

Polygenic inheritance involves multiple genes contributing to a single trait, whereas Mendelian inheritance typically involves a single gene. An example is skin color in humans, which is influenced by multiple genes.

What would the expected phenotypic ratio be for a cross involving incomplete dominance in Snapdragon flowers?

For a cross involving Snapdragon flowers with red (RR) and white (rr) parental plants, the offspring would show an intermediate phenotype (pink), resulting in a phenotypic ratio of 1:2:1 (red: pink: white) in subsequent generations.