IGCSE Biology Paper-3: Specimen Questions with Answers 337 - 338 of 358

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Question 337

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Explain the term codominance.

Explanation

  • Co-dominance works in multiple allele conditions.
  • In codominance, both the alleles of a gene are equally dominant i.e.. the dominant character is not able to suppress the recessive character & thus both the characters appear side by side in F1 hybrids. F1 generation resembles both the parents.
  • E. g. , ABO blood group.
  • Mendel considered that a single factor or gene controls a single character or trait or phenotype, but later it was found that a phenotype of character can be influenced by many genes and a gene can influence many phenotypes or traits.

Question 338

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Describe and explain the role of the placenta in relation to this problem.

Explanation

The maternal and fetal blood vessels are close enough within the placenta to allow for the transfer of nutrients, oxygen, and waste products; however, the two circulations do not mix. Once the baby is born, the placenta detaches from the uterine wall and is expelled from the body. When the placenta malfunctions, it՚s unable to supply adequate oxygen and nutrients to the baby from the mother՚s bloodstream. Without this vital support, the baby cannot grow and thrive. This can lead to low birth weight, premature birth, and birth defects. It also carries increased risks of complications for the mother.

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