Dominância incompleta e Co-Dominância - Aula 05 - Módulo 2: Genética

Summary

In this video, the professor explains key concepts in genetics, focusing on incomplete dominance and codominance. Through practical examples, such as flower colors and sickle cell anemia, viewers learn how these genetic principles influence inheritance. Incomplete dominance is explained with an example of pink flowers resulting from a red and white flower cross, while codominance is demonstrated with the contrasting black and white spots on cattle. The video also explores the significance of these genetic traits in the context of disease resistance, particularly in relation to malaria and sickle cell anemia, encouraging viewers to understand both theoretical and practical aspects of genetics.

Takeaways

• 😀 Incomplete dominance results in an intermediate phenotype, such as a pink flower from a red and white flower cross.
• 😀 Codominance occurs when both alleles are expressed simultaneously, like in the case of spotted cattle with black and white fur.
• 😀 Sickle cell anemia is caused by a mutation in hemoglobin, leading to sickle-shaped red blood cells.
• 😀 Individuals with the sickle cell trait (heterozygous) are more resistant to malaria but may have mild anemia.
• 😀 Sickle cell anemia is more common in regions with high malaria prevalence, offering a survival advantage in those areas.
• 😀 Incomplete dominance and codominance both show equal genotypic and phenotypic ratios in specific crosses.
• 😀 A cross between two heterozygous individuals (AS x AS) for sickle cell trait results in a 25% chance of having a child with sickle cell anemia (SS).
• 😀 The color of a person's skin does not affect the manifestation of sickle cell anemia; genetic information is the key factor.
• 😀 The codominance model in sickle cell anemia means the heterozygote expresses both normal and sickle-shaped red blood cells.
• 😀 Understanding genetics through real-life examples like sickle cell anemia helps illustrate how genetic traits can impact health and survival.

Q & A

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

Incomplete dominance, or semi-dominance, is when the heterozygote expresses an intermediate phenotype between the two parental phenotypes. For example, a cross between a red flower and a white flower might result in a pink flower. In contrast, codominance occurs when both alleles are fully expressed in the heterozygote, such as in sickle cell anemia, where both typical and sickle-shaped red blood cells are present.

How do lethal alleles relate to incomplete dominance and codominance?

Lethal alleles, which were discussed in the previous class, are not directly related to incomplete dominance or codominance but are another form of genetic inheritance that can result in the death of an organism when present in a certain combination. However, like incomplete dominance and codominance, lethal alleles follow Mendelian inheritance patterns.

What is the genotypic and phenotypic ratio for a cross involving incomplete dominance?

In a cross involving incomplete dominance, the genotypic ratio is the same as the phenotypic ratio. For example, if two heterozygous individuals are crossed (e.g., red x white flowers), the genotypic and phenotypic ratio would be 1:2:1—one red, two pink (intermediate), and one white.

Can you give an example of a codominance scenario?

A classic example of codominance is found in sickle cell anemia. Individuals with one allele for normal hemoglobin (HB A) and one allele for sickle cell hemoglobin (HB S) will express both types of hemoglobin in their red blood cells, leading to a mix of normal and sickle-shaped cells, without any intermediate phenotype.

How does the presence of malaria influence the prevalence of sickle cell anemia in regions like Mozambique?

Malaria, caused by the Plasmodium parasite, attacks red blood cells. Individuals with sickle cell anemia have sickle-shaped red blood cells that are resistant to the malaria parasite, leading to a higher prevalence of the sickle cell trait in regions like Mozambique, where malaria is common.

What happens when a person inherits the sickle cell trait?

A person who inherits one normal hemoglobin allele (HB A) and one sickle cell allele (HB S) becomes a carrier of the sickle cell trait. These individuals usually do not exhibit symptoms of sickle cell anemia, but they are more resistant to malaria compared to individuals with normal hemoglobin.

What is the life expectancy of individuals with sickle cell anemia?

Individuals with sickle cell anemia, who inherit two sickle cell alleles (HB S), usually have a significantly reduced life expectancy due to the complications caused by the disease, including severe anemia and circulatory problems due to blocked blood vessels.

How does the process of inheritance in codominance work using the example of red and white cows?

In codominance, if a white cow with genotype BB and a black bull with genotype BB are crossed, the offspring will express both the black and white traits. This results in a spotted or patched pattern, with both black and white areas visible in the offspring's phenotype.

In the case of sickle cell anemia, how does the heterozygous genotype influence red blood cell shape?

In the case of sickle cell anemia, a heterozygous individual with the genotype HB A/HB S will have both normal and sickle-shaped red blood cells. This is a characteristic of codominance, where both the normal and sickle-shaped cells are expressed.

What does the probability calculation for two heterozygous parents (AAS) having a child with sickle cell anemia reveal?

When two heterozygous parents (AAS) cross, there is a 25% chance that their child will inherit two sickle cell alleles (SS) and develop sickle cell anemia. This is based on the Mendelian Punnett square, where the possible genotypes of the offspring include AA, AS, and SS.