inheritance

• describe the differences between asexual and asexual reproduction

  • sexual - involves the fusion of a male and a female gamete (fertilisation), mixing of genetic information, variation in the offspring
  • asexual - only one parent, does not involve gametes, no mixing of genetic information, all off springs are identical, clones
• describe how meiosis halves the number of chromosomes in gametes

  • meiosis only takes place in reproductive organs
  • 23 chromosomes pairs are copied
  • divided into 2
  • divide one more time, chromosomes are single not paired
  • meiosis forms four gametes
• describe how fertilisation restores the full number of chromosomes

  gametes from male and female joins (fertilisation) the full number is restored as each gamete contains single chromosomes, however when joint they form a full 23 pair chromosomes
• describe the structure of DNA

  • chromosomes contain DNA, which determine our inherited features.
  • two strands
  • each strand is a polymer
  • double helix
• DNA is found in chromosomes and gene is a small section of DNA in a chromosome
• each gene encodes for a specific sequence of amino acids to make a specific protein
• human genome

  • help us understand and treat inherited disorders
  • trace human migration patterns
  • help search for genes that are linked to a disease
• alleles

  versions of a gene
• genotype

  tells us the alleles present
• homozygous

  two copies of the same allele
• phenotype

  tells us the characteristics caused by the person's allele
• heterozygous

  two different alleles
• dominant allele

  will show even if there is only one copy present
• recessive alleles

  will only show in the phenotype if two recessive alleles are present
• cystic fibrosis

  disorder of cell membrane
• carrier - if they have one normal cell membrane allele and one defective cell membrane allele
• polydactyly

  • extra fingers or toes
  • caused by dominant allele
  • cannot be a carrier
• embryo screening - embryos are tested to see if they have alleles for inherited disorder, if not are implanted into woman
• discuss the issues around embryo screening

  • expensive
  • large numbers of embryos are created but only a small number are implanted so sme healthy embryos are destroyed
  • produce offsprings with desirable feature in the future, unethical
• inheritance of sex

  • 22 pairs contains genes which only determine inherited characteristics
  • one pair contain a gene which determines their sex
  • males have XY chromosomes
  • females have XX chromosomes