11.4 Meiosis

Chromosome Number Chromosomes carry _________. Genes are located in specific positions on _____________.

Diploid Cells 2 1 1 2 Fruit flies have eight chromosomes. Four come from the father, four come from the mother. _________________– The two sets of chromosomes that match. Always ______ from each parent. 3 3 Why might chromosome 4 be different? X and Y chromosome (Larger X, smaller Y) 4 4

Diploid Cells _____________– Cell containing both sets of homologous chromosomes.  Represented by 2N. For the fruit fly, the diploid number is 8, which can be written as 2N = 8 All cells are diploid except the ________and ___________.

Haploid Cells Haploid (N) - cells containing ________________chromosomes, and therefore a single set of ___________. _______________ (sperm and egg) are haploid. Fruit flies are 2N with 8 chromosomes. How many chromosomes do the gametes have?

Meiosis I 23 Meiosis II

Phases of Meiosis Meiosis - process in which the number of chromosomes in a diploid cell is __________________. Made up of meiosis I and meiosis II. By the end of meiosis II, the diploid cell becomes ______________cells. Interphase Prophase I Metaphase I Anaphase I Telophase I Cytokinesis Prophase II Metaphase II Anaphase II Telophase II Cytokinesis Meiosis II Meiosis I

Interphase Meiosis I - Prophase I Chromosomes replicate Homologous chromosomes pair up. Form____________– four chromatids Go through crossing-over. Example cell: 2N (4 chromosomes) 

Prophase I – Crossing-Over First, homologous chromosomes cross over one another. Crossed sections of the chromatids are _____________________. Important because it produces _____________________ of alleles (genes).

Metaphase I Anaphase I Homologous chromosomes _______________________________________________. ________________________________are pulled apart and move towards opposite ends of the cell.

Cytokinesis Telophase I Nuclear membrane __________ around each cluster of chromosomes. Cells splits, forming ________________.

Meiosis I Concludes Results in _______________ daughter cells Each has 2 chromosomes, 4 chromatids. Each cell has different chromosomes than when it started because of crossing-over.

Meiosis II After meiosis I comes meiosis II. No interphase The final four phases of meiosis II are similar to those in meiosis I. However, ______________________________________________.

Metaphase II Prophase II _________________________. No tetrads Chromosomes ____________________________________________.

Telophase II, and Cytokinesis Anaphase II Paired chromatids ___________. Splits into __________________________________ Each has 2 chromosomes, 2 chromatids.

Interphase Prophase I Prophase II Metaphase I Metaphase II Meiosis II Anaphase I Telophase I Cytokinesis Prophase II Metaphase II Anaphase II Telophase II Cytokinesis Meiosis II Meiosis I 4 cells 2 chromosomes 2 chromatids 2 cells 2 chromosomes 4 chromatids

Gametes to Zygotes __________________— the fusion of the male and female gametes Makes a ______________. The zygote undergoes ____________ and eventually forms a new organism. Zygote has a new combinations of alleles

Sexual Reproduction + = Haploid (n) Gamete Ova (egg) Haploid (n) Gamete Sperm Diploid (2n) Zygote AKA Junior!

Comparing Meiosis and Mitosis Daughter cells have Results in

Chromosomal Mutations _____________ ____________(part of chromosome breaks off) ______________(breaks off, reattaches upside down) ______________ (breaks off, reattaches on another chromosome)

Gene Linkage and Gene Maps How can two alleles from different genes be inherited together? Alleles from different genes tend to be inherited together when those genes are located ___________________________.

Gene Linkage A scientist used a fly with reddish-orange eyes and miniature wings in a series of test crosses. His results showed that the genes for those two traits were almost always inherited together. Morgan discovered that many of them appeared to be “linked” together in ways that seemed to violate the principle of independent assortment.

Gene Linkage Findings led to two conclusions: First, each chromosome has groups of ___________________ Second, it is the _________________ that assort independently, not individual ___________. Alleles of different genes tend to be inherited together when those genes are _____________ ___________________________.

Gene Mapping Sturtevant wondered could gene linkage be a clue to the genes’ locations? Sturtevant reasoned if two genes are located ____________together, then crossovers between them should be rare. If two genes are located _______________, then crossovers between them should be common.

Gene Mapping Used the frequency of cross-overs between genes to determine their distances from each other. Method still used today.