Meiosis and variation

You should be able to: Relate their understanding of the cell cycle to cancer and its treatment

Cancer The likelihood of developing cancer increases with age. There are many different forms. Normally the cell cycle and mitosis are regulated by genes. If these become damaged it can result in uncontrolled cell division. A group of abnormal cells forms a tumour.

Types of tumour Benign Slow growing Stay within one tissue Are not life threatening Malignant Grow rapidly Invade surrounding tissues and can spread around the body Are life threatening Unless treated at early stage

Causes Carcinogens Radiation Viral infections Genetic predispostion

Treatments include: S phase - Preventing DNA from replicating. Inhibiting metaphase by interfering with spindle formation. G 1 (cell growth and protein production) – some chemical drugs (chemotherapy), prevent synthesis of enzymes needed for DNA replication. So cell is unable to enter synthesis (S) phase so cell cycle is disrupted and cell kills itself.

Meiosis-Objectives Understand the importance of meiosis in producing cells which are genetically different. Know that it forms haploid cells Know that independent segregation of homologous chromosomes occurs. Therefore gametes are genetically different as a result of different combinations of maternal and paternal chromosomes. Understand that crossing over results in genetic recombination

words Ovaries diploid Testes zygote Haploid interphase

Ovary Testis Sexual Reproduction

Crossing over

Independent assortment

Outcome of meiosis Meiosis produces haploid gametes which are genetically different. They have different combinations of maternal and paternal chromosomes They have different combinations of alleles due to crossing over

Variation-objectives You should understand that similarities and differences between individuals within a species are due to genetic, environmental factors or both. The need for random sampling The concept of a normal distribution about a mean and standard deviation