Section 3The Cell and InheritanceByMr Hamdy Karim
• Key Concepts• What role do chromosomes play ininheritance?• What events occur during meiosis?• What is the relationship betweenchromosomes and genes?
Chromosomes and Inheritance• 1903- Walter Sutton was studying chromosomes ingrasshoppers.• Found that the body cells of grasshoppers have 24chromosomes, but the sex cells only had 12( exactly half)
Chromosome pairs Sutton observed that when asperm cell and an egg cell joinedin fertilization the resultingfertilized egg again had 24chromosomes. Chromosomes exist in pairs. Onechromosome in each pair camefrom the male parent and onecame from the female parent
Genes on Chromosomes• Sutton knew that alleles exist in pairs in anorganism and one alleles comes from thefemale parent and the other from the maleparent• Sutton realized that the paired alleles arecarried on paired chromosomes• Chromosome theory of inheritance – genesare carried from parents to offspring onchromosomes
Meiosis• Meiosis – the process by which the number ofchromosomes is reduced by half to form sex cells –sperm and egg• The chromosome pairs separate and are distributedto two different cells• Each of these 2 cells has half the number ofchromosomes, but these chromosomes still have 2chromatids• In the second part of Meiosis, these chromatidsseparate and the cells divide resulting in 4 sexcells, each with half the number of chromosomes ofthe original cell
Meiosis and Punnett squares• Punnett squares show what occurs duringmeiosis• When chromosome pairs separate and gointo different sex cells, so do the alleles, too
A Lineup of Genes• Human body cells have 23 pairsof chromosomes or 46. Eachchromosome has many genes.(around 35,000 total)• Each gene controls a trait• One chromosome pair is fromthe female parent and one isfrom the male parent