chromosomes

• Humans have 23 pairs of chromosomes, with one set coming from each parent during fertilization.
• Chromosomes are structures made up of DNA and proteins that carry genes and determine inherited traits.
• chromosomes are x-shaped
• karyotype: picture of all chromosomes
• homologous chromosomes: chromosomes with the same genes but not necessarily the same alleles
• mutation: a spontaneous change in a gene or chromosome
• mutation often occurs during replication
• most mutations are harmful e.g. cancer
• some mutations are non-harmful e.g. the granny smith apple
• XX - female
• XY - male
• all eggs contain an X chromosome
• sperm can contain either an X or Y chromosome
• any genes located on sex chromosome are called sex-linked inheritance
• why are sex-linked traits more common in males than females?

  a recessive allele on the X chromosome will always produce the trait in a male since males only have one X chromosome
• mutagens increase risk of mutation
• gametes have 23 chromosomes
• somatic cells have 46 chromosomes