Hi, i have some doubts i would like to clear. What is the difference between codominance, incomplete dominance, and complete dominance?? i'm getting rather confused.
What type of gene is the sickle cell anemia? Say r stands for the recessive allele for sickle cell anaemia, and R for normal allele, then a heterozygous person, Rr, would she just be a carrier without any sickle cell, or would she have less sickle cells than a homozygous recessive person, rr?
I'm rather confused about the blood type thing as well! (A, B, O and AB)
Please help! Thankyou
Bailey, Andrea, Danny, Riley, anabelle, holly, LILLY, zachary, I'm stumped -- or whoever!
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Sure! I'll explain the concepts of codominance, incomplete dominance, and complete dominance, and then address your questions about sickle cell anemia and blood types.
1. Codominance:
In codominance, both alleles of a gene are fully expressed in the phenotype of a heterozygous individual. This means that neither allele is dominant or recessive over the other, and they both contribute to the observed trait. For example, in humans, the ABO blood type system demonstrates codominance. If an individual has both A and B alleles, they will express both A and B antigens on their red blood cells, resulting in blood type AB.
2. Incomplete Dominance:
In incomplete dominance, the phenotype of the heterozygous individual is an intermediate blend between the phenotypes of the two homozygous individuals. The heterozygous phenotype is not completely dominant or recessive but falls somewhere in between. For example, in snapdragons, if a red-flowered plant (RR) crosses with a white-flowered plant (rr), the resulting offspring will have pink flowers (Rr).
3. Complete Dominance:
In complete dominance, one allele is completely dominant over the other, and the phenotype of the heterozygote is the same as that of one of the homozygotes. The dominant allele masks the expression of the recessive allele. For example, in Mendel's pea plant experiments, when a dominant allele for tall height (T) crosses with a recessive allele for short height (t), the heterozygous genotype (Tt) will express the dominant tall phenotype.
Now, moving on to your question about sickle cell anemia:
Sickle cell anemia is caused by a recessive allele, represented by the lowercase letter "r." The normal allele is represented by the uppercase letter "R." A person who is heterozygous (Rr) for the sickle cell gene is considered a carrier, meaning they have one copy of the sickle cell allele but do not manifest the disease. A homozygous recessive individual (rr) will have two copies of the sickle cell allele and thus have the full-blown sickle cell anemia.
Finally, let's discuss blood types (A, B, O, and AB):
The ABO blood type system involves three alleles: A, B, and O. A person may have blood type A (AA or AO), blood type B (BB or BO), blood type AB (AB), or blood type O (OO). The A and B alleles are codominant, meaning they can both be expressed simultaneously. The O allele is recessive, and its presence results in the type O blood. A person with type A blood has the A antigen, type B blood has the B antigen, type AB blood has both A and B antigens, and type O blood lacks both A and B antigens.
I hope this explanation helps clarify the differences between codominance, incomplete dominance, and complete dominance, as well as answers your questions about sickle cell anemia and blood types. Let me know if you have any further doubts!