1. Chromosomes   Aims:   Must be able to state what gametes are and where they come from.   Should be able to state what chromosomes are and describe their possible structures.   Could be able to outline some of the possible chromosome mutations and their effects.

2. Binary Fission   In prokaryotic cells there are no membrane bound organelles.   A single-stranded DNA molecule as a circular chromosome is located in the cytoplasm.   Small rings of DNA as rings (PLASMIDS) are also located in the cytoplasm.   Replication in Prokaryotes is replication of DNA strand followed by a separation of the cell into two.

3. Gametes   Refers to both ovum and sperm cells.   Formed as a result of Meiosis.   Contains only half of the full set of genetic instructions of the individual (HAPLOID).   The ovaries of the female and the testes of the male are specialised organs (Gonads).   It is within these organs that the process of meiosis occurs. Gamete Production

4. Fertilisation   After fertilisation, the nuclei of the sperm and egg fuse.   The resultant fertilised egg now contains the double set of genetic material = full set of instructions for the developing embryo (DIPLOID).

5. Chromosomes   Genetic information (DNA) is packaged in each cell in the form of Chromosomes.   Each chromosome is one DNA molecule tightly wound and packaged into a more compact form.   Chromosomes exist in Somatic cells (body cells other than gametes) in pairs.

6. Chromosome Structure   Histone proteins organise the DNA into tightly coiled structures (visible chromosomes) during cell division.   Coiling into compact structures allows the chromatids to separate without tangling during cell division. Cell DNA molecule (double helix comprising genes) Individual atoms Histone proteins Replicated chromosome Chromatin: a complex of DNA and protein

7. Homologous Chromosomes   Diagram illustrates the complete chromosome complement for a hypothetical organism.   Total of ten chromosomes, comprising five nearly identical pairs (each pair is numbered). Paternal chromosome that originated from the sperm of this individual's father Maternal chromosome that originated from the egg of this individual's mother

8. Numbers of Chromosomes   Chromosome numbers vary considerably between organisms.   The numbers may differ markedly between species that are closely related. OrganismsChromosome No. human46 chimpanzee48 gorilla48 cattle60 cat38 goldfish94 Drosophila8 honey bee32 or 16 Hydra32

9. Human Karyotype   Karyotypes - display chromosome contents of a cell, organised by number, size and type.   Normal somatic human cells - karyotype with 46 chromosomes (23 pairs) comprising:   22 pairs of autosomes.   1 pair of sex chromosomes. These determine the sex of an individual: XX = female XY = male 123 45 6 78 91010 1 1212 1313 1414 1515 1616 1717 1818 1919 2020 21212 YX

10. Male and Female Karyotypes   Every cell (except sperm cells) in a normal human male has:   44 autosomes   2 sex chromosomes   Every cell (except egg cells) in a normal human female has:   44 autosomes   2 sex chromosomes

11. Activity   Complete the cut and stick activity.

12. Chromosomes and Genes   A single chromosome may contain hundreds of genes. 1 El Rh AMY Fy 1270 Chromosome: No. of genes: TYS 4 MN 465 9 ABO NP 499 13 RB 195 X CBD HEMA 773

13. Chromosome Features   Chromosomes can be identified by noting:   Banding patterns   Position of the centromere   Presence of satellites   Length of the chromatids   Features enable homologous pairs to be matched and accurate karyotypes made. Metacentric Submetacentric or Subterminal Acrocentric

14. Changes within Chromosomes   Chromosomes can be mutated in 4 main ways:   Deletion:   Inversion:   Duplication:   Insertion:   Translocation: Part of chromosome is moved to a new region within the Karyotype.   These will cause a change in the gene product or an altered or inactive protein.

15. Changes in Number of Chromosomes   Some individuals have an abnormal number of chromosomes (ANEUPLOIDY) in their cells.   Additional chromosome – Trisomic (trisomy) – Embryonic Death except 13, 18, 21 or Sex Chromosomes.   Missing Chromosome – Monosomic (monosomy) – Embryonic Death except Sex Chromosome

16. Activity   Complete the Biozone pages 261, 264 to 268.