GENETICS 101 (Part 3) | Definitions, Albinism, Sickle Cell Anaemia| CXC Biology Tutor

Summary

This video explains the inheritance of genetic traits, focusing on complete dominance, incomplete dominance, and specific conditions like sickle-cell anemia. The presenter uses Mendelian genetics to demonstrate how traits such as flower color and hemoglobin are inherited through allele combinations. In the case of sickle-cell anemia, the video highlights how carriers of the sickle-cell trait have a mix of normal and sickle-shaped red blood cells, along with the protection they gain against malaria. The video offers clear examples through Punnett squares to illustrate the genetic outcomes and phenotypic ratios.

Takeaways

• 😀 Incomplete dominance occurs when neither allele completely dominates the other, resulting in an intermediate phenotype, like pink flowers from red and white parents.
• 😀 The phenotypic ratio for incomplete dominance in flower color, when crossing two pink flowers, is 1 red : 2 pink : 1 white.
• 😀 Sickle-cell anemia is caused by a mutation in the hemoglobin gene, resulting in sickle-shaped red blood cells, which leads to various health issues.
• 😀 Normal hemoglobin (E) and abnormal hemoglobin (S) alleles are represented in the genetics of sickle-cell anemia.
• 😀 A person with two normal alleles (EE) has normal red blood cells, while those with two abnormal alleles (SS) have sickle-cell anemia.
• 😀 Individuals with one normal and one abnormal allele (ES) have the sickle-cell trait, showing a mix of normal and sickle-shaped red blood cells.
• 😀 In a cross between two heterozygous sickle-cell trait parents (ES × ES), the possible offspring include: 1 with normal hemoglobin (EE), 2 with the sickle-cell trait (ES), and 1 with sickle-cell anemia (SS).
• 😀 The inheritance of sickle-cell anemia follows a 1 : 2 : 1 phenotypic ratio for normal, carrier, and affected individuals.
• 😀 People who carry the sickle-cell trait (ES) have a protective advantage against malaria due to the malaria parasite's inability to survive in sickle-shaped red blood cells.
• 😀 The video aims to clarify the concepts of complete and incomplete dominance in genetics, using examples such as flower color and sickle-cell anemia to illustrate these patterns.
• 😀 Future content will focus on the inheritance of blood groups and sex-linked traits, continuing the exploration of genetic inheritance patterns.

Q & A

What is incomplete dominance?

Incomplete dominance occurs when the alleles for a gene don't completely mask each other, resulting in a blending of traits. For example, crossing red and white flowers can produce pink flowers, which is a mix of both traits.

What is the phenotypic ratio for incomplete dominance in the example with red, pink, and white flowers?

The phenotypic ratio is 1 red flower : 2 pink flowers : 1 white flower. This shows that for every two pink flowers, one red and one white flower would be produced.

What causes sickle cell anemia?

Sickle cell anemia is caused by a mutation in the hemoglobin gene, leading to abnormal hemoglobin that causes red blood cells to take on a sickle shape, which can impair blood flow and oxygen delivery.

What are the alleles used to represent normal and abnormal hemoglobin in sickle cell anemia?

The allele 'E' represents normal hemoglobin, while the allele 'S' represents abnormal hemoglobin associated with sickle cell anemia.

What is the phenotypic result for a person who is homozygous for the 'E' allele?

A person who is homozygous for the 'E' allele (EE) will have normal hemoglobin and normal red blood cells.

What happens to someone who is heterozygous (ES) for sickle cell anemia?

A heterozygous individual (ES) will have a combination of normal and sickle-shaped red blood cells. This person carries the sickle cell trait but does not have the full-blown condition.

What is the genetic outcome of two heterozygous parents (ES) for sickle cell anemia?

When two heterozygous parents (ES) have children, the potential outcomes for the offspring include 1/4 chance of normal hemoglobin (EE), 2/4 chance of being a carrier (ES), and 1/4 chance of having sickle cell anemia (SS).

What is the significance of sickle cell trait in relation to malaria?

People with sickle cell trait (ES) have some protection against malaria. The malaria parasite struggles to survive in sickle-shaped red blood cells, providing an evolutionary advantage in regions where malaria is prevalent.

What is the typical Punnett square setup for two heterozygous sickle cell parents?

In a Punnett square for two heterozygous parents (ES), you would have four possible genotypic outcomes: EE, ES, ES, and SS, leading to a 1:2:1 phenotypic ratio of normal, carrier, and sickle cell anemia.

What is the importance of understanding incomplete dominance and sickle cell inheritance in genetics?

Understanding incomplete dominance and sickle cell inheritance helps explain how genetic traits are passed down, how some conditions like sickle cell anemia manifest, and how certain genetic traits may offer protective advantages in specific environments.