The Cell and Inheritance Key Concepts What role do chromosomes play in inheritance? What events occur during meiosis? What is the relationship between chromosomes and genes? Key Terms Meiosis

Chromosomes and Inheritance 1903- Walter Sutton was studying chromosomes in grasshoppers. Found that the body cells of grasshoppers have 24 chromosomes, but the sex cells only had 12 ( exactly half)

Chromosome pairs Sutton observed that when a sperm cell and an egg cell joined in fertilization the resulting fertilized egg again had 24 chromosomes. Chromosomes exist in pairs. One chromosome in each pair came from the male parent and one came from the female parent

Genes on Chromosomes Sutton knew that alleles exist in pairs in an organism and one alleles comes from the female parent and the other from the male parent Sutton realized that the paired alleles are carried on paired chromosomes Chromosome theory of inheritance – genes are carried from parents to offspring on chromosomes

Meiosis Meiosis – the process by which the number of chromosomes is reduced by half to form sex cells – sperm and egg The chromosome pairs separate and are distributed to two different cells Each of these 2 cells has half the number of chromosomes, but these chromosomes still have 2 chromatids In the second part of Meiosis, these chromatids separate and the cells divide resulting in 4 sex cells, each with half the number of chromosomes of the original cell

Meiosis Meiosis animation

Meiosis and Punnett squares Punnett squares show what occurs during meiosis When chromosome pairs separate and go into different sex cells, so do the alleles, too

A Lineup of Genes Human body cells have 23 pairs of chromosomes or 46. Each chromosome has many genes. (around 35,000 total) Each gene controls a trait One chromosome pair is from the female parent and one is from the male parent

Sources http://www.grasshoppercontrol.com/ http://www.todayinsci.com/11/11_10.htm http://www.accessexcellence.org/RC/VL/GG/images/genes.gif