Question #1 What must occur in order for Mendel s principles to hold true?

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2 Question #1 What must occur in order for Mendel s principles to hold true? An organism with two parents must inherit a single copy of every gene from each parent When that organism produces gametes, those two sets of genes must be separated so that each gamete contains just one set of genes Chromosomes are the carriers of genes, therefore, chromosomes must be separated

3 Question #2 What is a diploid cell? Diploid = Two sets Diploid cells of most adult organisms contain two complete sets of inherited chromosomes (homologous chromosomes) and two complete sets of genes Homologous chromosomes are the two sets of chromosomes (one from the male parent and one from the female parent)

4 Question #2 What is a diploid cell?

5 Question #3 What is a haploid cell? Haploid = One set Haploid cells contain only a single set of chromosomes, and therefore a single set of genes The gametes of sexually reproducing organisms are haploid

6 Question #4 What is meiosis? Process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell One diploid cell goes through two separate divisions, producing four haploid cells

7 Question #5 Human Cell 2N = 46 Sperm cells (N) have 23 chromosomes Egg cells (N) have 23 chromosomes

8 Question #6 What happens prior to meiosis I? The cell undergoes a round of chromosome replication during interphase Each replicated chromosome consists of two identical chromatids, joined at the centromere

9 Question #7 PROPHASE I Spindle forms in the cell Each replicated chromosome pairs with its corresponding homologous chromosome This pairing forms a structure called a tetrad Crossing over occurs during prophase I In crossing-over, sections of non-sister chromatids are exchanged (this produces new combinations of alleles in the cell)

10 Question #7 PROPHASE I CROSSING OVER

11 Question #7 PROPHASE I Tetrad (homologous chromosomes) consisting of 2 sets of sister chromatids

12 Question #7 METAPHASE I Paired homologous chromosomes line up across the center of the cell The spindle fibers attach to each tetrad

13 Question #7 ANAPHASE I Spindle fibers pull each homologous chromosome pair toward opposite ends of the cell

14 Question #7 TELOPHASE I and CYTOKINESIS A nuclear membrane forms around each cluster of chromosomes Cytokinesis follows telophase I, forming two new cells Each cell has ½ the genetic material of the original parent cell

15 Question #7 PROPHASE II The spindle reforms in both of the cells that were created during meiosis I

16 Question #7 METAPHASE II Chromosomes (paired sister chromatids) line up in the center of the cell

17 Question #7 ANAPHASE II The paired chromatids separate

18 Question #7 TELOPHASE II and CYTOKINESIS The nucleus begins to reform around the chromosomes in each cell Cytokinesis of meiosis II results in four haploid daughter cells

19 Question #8 Gamete to Zygote MEIOSIS MITOSIS MITOSIS Sperm (N) Egg (N) Zygote (2N)

20 Question #9 Mitosis and Similarities Both are preceded by a complete copying, or replication, of the genetic material Both have spindles Both have the movement of chromosomes

21 Question #9 Mitosis and Differences Mitosis has one cell division (meiosis has two cell divisions) Mitosis produces two cells (meiosis produces four cells) Mitosis only has sister chromatids line up and separate (meiosis has homologous chromosomes line up and then sister chromatids line up) Mitosis maintains the chromosome number (meiosis cuts the chromosome number in half Mitosis ends with two diploid cells (meiosis ends with four haploid cells)

22 Question #10 Thomas Hunt Morgan s Conclusions Each chromosome is actually a group of linked genes Chromosomes assort independently (not the individual genes) Alleles for different genes tend to be inherited together from one generation to the next when those genes are located on the same chromosome

23 Question #11 Alfred Sturtevant s Conclusion The farther apart two genes were on a chromosome, the more likely it would be that crossing-over would occur between them If two genes are close together, then crossovers between them should be rare If two genes are far apart, then crossovers between them should be more common He used the frequency of crossing-over between genes to determine their distances from each other (and he also created gene maps from that data)

24 Question #12 Curved and dumpy OR Curved and vestigial (small) Curved wing and dumpy wing are more likely to cross over The farther apart, the more likely crossing-over will occur

25 Question #13 Least likely to cross over Purple eye and Light eye are the least likely to cross over The closer together the genes are, the less likely they are to cross over

26 Question #14 Gene Map In which gene map is the probability of crossing-over between A and D greatest? Number

27 Question #15 Gene Map In which gene map is the probability of crossing-over between A and D the least? Number

28 Question #16 Gene Map In which map are genes C and D most closely linked? Number

29 Question #17 Gene Map In map 4, which genes are least likely to cross over? C and B