inheritance

• what is a gamete?

  • a reproductive cell of an animal or plant
• what is a chromosome?

  • thin strands of DNA
• what is a gene?

  • a section of DNA that controls part of a cells chemistry, specifically protein production
• what is an allele?

  • different version of the same gene
• what does dominant mean?

  • it is always expressed, even if only one copy is present.
• what does recessive mean?

  • only expressed if two copies are present, no dominant allele is present
• homozygous meaning?

  • having two identical alleles for the same characteristic
• heterozygous meaning?

  • two alleles of a particular gene being different
• genotype meaning

  • the combination of alleles that an organism has for a particular gene
• phenotype meaning

  • the physical characteristics of an organism
• some characteristics are controlled by a single gene, such as fur colour in mice, and red-green colour blindness in humans. each gene may have different forms called alleles

  the alleles present, or genotype, operate at a molecular level to develop characteristics which is the phenotype
• polydactyly is caused by a dominant allele and cystic fibrosis is caused by a recessive allele.
• for embryonic screening

  • reduce suffering
  • treating disorders costs the government and taxpayers a lot of money
  • laws in place to stop it going too far
• against embryonic screening

  • implies that people with genetic issues are undesirable - increasing prejudice
  • may come aa point where everyone wants to screen their embryos to pick the most desirable one
  • expensive
• what is embryonic screening?

  • before an embryo is implanted in IVF, it is possible to remove a cell from each embryo to screen for genetic disorders
  • many can be detected including cystic fibrosis
  • DNA can also be taken from the womb fro screening
• sex determination

  • ordinary human body cells contain 23 pairs of chromosomes. 22 pairs control characteristics only but one pair carries the genes that determine sex.
  • in females, the sex chromosomes are the same (XX)
  • in males, they are different (XY)