1. Meiosis Reduction Division

2. Genetics Vocabulary Gene: –a discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses) at a specific locus (location) Allele: –Any of the alternative versions of a gene that produce distinguishable phenotypic (visible) effects Genome: –The genetic material of an organism or a virus; the complete complement of an organism’s or viruses genes along with its noncoding nucleic acid sequences

3. Meiosis Vocabulary Diploid cell: –a cell that contains all (2n) of the genetic info it should. Haploid cell: –a cell that contains half (n) of the genetic info it should. Homologous chromosomes: –“paired”(at the same locus) chromosomes that have the same traits arranged in the same order but the are not identical Meiosis: –The process that creates cells with a haploid number of genetic info.

4. Meiosis Vocabulary Gametes: –The only cells in the body not produced by mitosis –Made in the gonads –Sex cells Sperm: The male sex cell Egg: The female sex cell Each one represents 1 in 8.4 million possible genetic combinations Zygote: –The result of sperm fertilizing egg. –Combo of sperm and egg makes a 1 in 70 trillion possible combinations Somatic cell: –Any other cell other than those involved in gamete formation

5. Miscellaneous Factoids Typically, a thousand or more genes are arranged on each chromosome Humans have 46 chromosomes Why meiosis? Offspring get information from mom and dad –Genetic diversity is key!! If that info wasn’t split, you would get twice as much information as they would have (reduction division)

6. Phases Interphase The same as interphase in mitosis Chromosomes replicate Each chromosome then has two identical sister chromatids held together by a centromere

7. Prophase I Chromosomes coil Spindle forms Tetrads are formed –Joining of two homologous chromosomes with two sister chromatids each (called synapsis) –Bind so tightly that information is exchanged Now called Chiasmata (Chiasma) –Called Crossing over (remember the purpose of introns!!!) Forms recombinant chromosomes

8. Metaphase I Tetrads line up at midline Homologous chromosomes line up in pairs

9. Anaphase I Homologous chromosomes separate and migrate towards poles Centromeres do not split –This ensures that each new cell gets only one chromosome

10. Telophase I Spindle breaks down Chromosomes uncoil Cytoplasm divides (cytokinesis) Cell has half of original cells genetic info but still double the amount it should

11. Interphase II** Very short or non-existent Chromosomes do not replicate

12. Meiosis II Prophase II –Spindle forms Metaphase II –Sister chromatids line up at the equator Anaphase II –Centromeres split –Sister chromatids split Telophase II –Spindle breaks down –New nuclei form –Cytokinesis occurs

13. Meiosis in Men and Women Male version of meiosis Spermatogenesis 4 sperm cells for every 1 cell that divides Female version of meiosis Oogenesis 4 egg (ova) cells for every 1 cell that divides 3 die and 1 survives

14. Meiosis is the same all around the world!

15. Alternation of Generations The adult generation produces spores, while the spore generation produces sex cells. Only seen in plants.

16. Errors DNA mutations –Point Base-pair substitution –Silent mutations »Harmless »Occur within non-coding areas or don’t affect the coded polypeptide –Missense mutations »Amino acid works but not the way it’s supposed to (i.e., “close but no cigar”) –Nonsense mutations »Functionless amino acid »Example: a premature stop code Base-pair insertions/deletions –Almost always lead to frameshift mutations

17. Errors Chromosomal –Nondisjunction Leads to aneuploidy (abnormal # of chromsomes) –Trisomic (2n+1) –Monosomic (2n-1) Polyploidy –Triploidy (3n) –Tetraploidy (4n) (gray tree frog) –Chromsomal structure alterations Deletion Duplication Inversion translocation

18. Examples of Aneuploidy Trisomy 21: Down’s syndrome

19. Examples of Aneuploidy Trisomy 13: Patau syndrome (heart and kidney defects among problems)

20. Examples of Aneuploidy Trisomy 18: Edwards syndrome (body wide effects)

21. Examples of Aneuploidy Klinefelter syndrome: XXY

22. Examples of Aneuploidy XYY syndrome: –Not defined as syndrome –taller than average –Violent tendencies? (Chino prison study)

23. Examples of Aneuploidy XXX syndrome: relatively normal

24. Karyotyping

25. Chorionic villus sampling &Amniocentesis