Lesson Overview 11 4 Meiosis Lesson Overview Meiosis

Lesson Overview 11. 4 Meiosis

Lesson Overview Meiosis THINK ABOUT IT Ø As geneticists in the early 1900 s applied Mendel’s laws, they wondered where genes might be _____. Ø They expected genes to be carried on structures inside the cell, but _________? Ø What cellular processes could account for segregation and independent assortment, as Mendel had described?

Lesson Overview Meiosis Chromosome Number ØHow many sets of genes do multicellular organisms inherit? ØThe _____ cells of most adult organisms contain _______ of inherited chromosomes and _________of genes.

Lesson Overview Meiosis Chromosome Number Ø________—those strands of DNA and protein inside the cell nucleus—are the carriers of ______. ØThe genes are located in _________on chromosomes.

Lesson Overview Meiosis Diploid Cells Ø A body cell in an adult fruit fly has _____, as shown in the figure. Ø ____ of the chromosomes come from its male parent, and ______ come from its female parent. Ø These two sets of chromosomes are _________, meaning that each of the four chromosomes from the male parent has a corresponding chromosome from the female parent.

Lesson Overview Meiosis Diploid Cells Ø A cell that contains both sets of homologous chromosomes is____, meaning “two sets. ” Ø The diploid number of chromosomes is sometimes represented by the symbol ___. Ø For the fruit fly, the diploid number is 8, which can be written as ____, where N represents twice the number of chromosomes in a sperm or egg cell.

Lesson Overview Meiosis Haploid Cells Ø Some cells contain only a single set of chromosomes, and therefore a single set of genes. Ø Such cells are ______, meaning “one set. ” Ø The ________ of sexually reproducing organisms are _______. Ø For fruit fly gametes, the haploid number is ___, which can be written as ____.

Lesson Overview Meiosis Phases of Meiosis Ø_____ is a process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. ØMeiosis usually involves two distinct divisions, called ______and _______. ØBy the end of meiosis II, the diploid cell becomes __________ cells.

Lesson Overview Meiosis I Ø Just prior to meiosis I, the cell undergoes a round of chromosome replication called ________. Ø Each replicated chromosome consists of _____________ joined at the center.

Lesson Overview Meiosis Prophase I Ø ___________ pair to form a _______

Lesson Overview Meiosis Prophase I Ø As homologous chromosomes pair up and form tetrads, they undergo a process called ________. Ø First, the chromatids of the __________________cross over one another.

Lesson Overview Meiosis Prophase I Ø Then, the crossed sections of the chromatids are _________. Ø Crossing-over is important because it produces __________________ in the cell. Ø As prophase I ends, a ________ and attaches to each ________.

Lesson Overview Meiosis Metaphase I Ø During ________of meiosis, paired homologous chromosomes ___________________.

Lesson Overview Meiosis Anaphase I Ø During ______, spindle fibers pull each homologous chromosome pair toward opposite ends of the cell. Ø When anaphase I is complete, the separated chromosomes ______ at opposite ends of the cell.

Lesson Overview Meiosis Telophase I and Cytokinesis Ø During _______, a nuclear membrane forms around each cluster of chromosomes. Ø __________ follows telophase I, forming two new cells.

Lesson Overview Meiosis I Ø Meiosis I results in two cells, called _______, each of which has _____ the number of chromosomes (2 _______ cells). Ø Because each pair of homologous chromosomes was separated, neither daughter cell has the two complete sets of chromosomes that it would have in a diploid cell. Ø The two cells produced by meiosis I have sets of chromosomes and alleles that are ____ from each other and from the diploid cell that entered meiosis I.

Lesson Overview Meiosis II Ø The two cells produced by meiosis I now enter a __________. Ø Unlike the first division, no _______ occurs between meiosis I and meiosis II.

Lesson Overview Meiosis Prophase II Ø As the cells enter prophase II, their chromosomes—each consisting of ____________—become _______. Ø The chromosomes ___________ to form tetrads, because the homologous pairs were already separated during meiosis I.

Lesson Overview Meiosis Metaphase II ØDuring metaphase II of meiosis II, chromosomes ______ of each cell.

Lesson Overview Meiosis Anaphase II Ø As the cell enters anaphase II, the ___________.

Lesson Overview Meiosis Telophase II, and Cytokinesis ØIn the example shown here, each of the ___________ produced in meiosis II receives two __________.

Lesson Overview Meiosis Telophase II, and Cytokinesis ØThese four daughter cells now contain the _________ just two chromosomes each.

Lesson Overview Meiosis Gametes to Zygotes ØThe haploid cells produced by meiosis II are _________. ØIn male animals, these gametes are called _____. In some plants, _______ contain haploid sperm cells. ØIn female animals, generally one of the cells produced by meiosis is involved in reproduction. The female gamete is called an _____ in animals and an ______ in some plants.

Lesson Overview Meiosis Gametes to Zygotes ØFertilization—the fusion of male and female gametes—generates new combinations of alleles in a _______. ØThe zygote undergoes cell division by _____ and eventually forms a new organism.

Lesson Overview Meiosis Comparing Meiosis and Mitosis ØHow is meiosis different from mitosis? Ø In mitosis, when the two sets of genetic material separate, each daughter cell receives one _________________. ØIn meiosis, _____________to separate daughter cells.

Lesson Overview Meiosis Comparing Meiosis and Mitosis ØHow is meiosis different from mitosis? ØMitosis does not change the __________of the original cell. Ø Meiosis, _____________________________.

Lesson Overview Meiosis Comparing Meiosis and Mitosis Ø How is meiosis different from mitosis? Ø Mitosis results in the production of two __________ diploid cells Ø Meiosis produces four _______________ haploid cells.

Lesson Overview Meiosis Comparing Meiosis and Mitosis ØMitosis is a form of ________________ ØMeiosis is an early step in ______________. ØThere are three other ways in which these two processes differ.

Lesson Overview Meiosis Replication and Separation of Genetic Material ØIn ________, when the two sets of genetic material separate, each daughter cell receives ___________ of chromosomes.

Lesson Overview Meiosis Replication and Separation of Genetic Material Ø In meiosis, ___________ line up and then move to separate daughter cells. Ø As a result, the ________ for each _____________ from each other and end up in different cells.

Lesson Overview Meiosis Replication and Separation of Genetic Material ØThe sorting and recombination of genes in ________ result in a greater variety of possible gene combinations than could result from mitosis.

Lesson Overview Meiosis Changes in Chromosome Number Ø______ does not normally change the chromosome number of the original cell. Ø________ reduces the chromosome number by half.

Lesson Overview Meiosis Changes in Chromosome Number Ø A diploid cell that enters mitosis with ____ chromosomes will divide to produce two diploid daughter cells, each of which also has _______ chromosomes.

Lesson Overview Meiosis Changes in Chromosome Number ØOn the other hand, a diploid cell that enters meiosis with _______chromosomes will pass through ____meiotic divisions to produce _________, each with only ______ chromosomes.

Lesson Overview Meiosis Number of Cell Divisions ØMitosis is a ______ cell division, resulting in the production of two __________daughter cells.

Lesson Overview Meiosis Number of Cell Divisions ØMeiosis requires ____ rounds of cell division, and, in most organisms, produces a total of ____________________daughter cells.

Lesson Overview Meiosis Gene Linkage and Gene Maps Ø How can two alleles from different genes be inherited together? Ø Alleles of different genes tend to be inherited together from one generation to the next when those genes are located on the _____________.

Lesson Overview Meiosis Gene Linkage Ø ________ research on fruit flies led him to the principle of_______. Ø After identifying more than 50 Drosophila (fruit fly) genes, Morgan discovered that many of them appeared to be “______” together in ways that seemed to violate the principle of independent assortment.

Lesson Overview Meiosis Gene Linkage ØFor example, Morgan used a fly with reddishorange eyes and miniature wings in a series of test crosses. ØHis results showed that the genes for those two traits were almost always ________. ØOnly rarely did the genes separate from each other.

Lesson Overview Meiosis Gene Linkage Ø Morgan and his associates observed so many genes that were inherited together that, before long, they could group all of the fly’s genes into ____________. Ø The linkage groups assorted independently, but all of the genes in one group were _____________. Ø As it turns out, Drosophila has four linkage groups and four pairs of chromosomes.

Lesson Overview Meiosis Gene Linkage Ø Morgan’s findings led to two remarkable conclusions: Ø First, each chromosome is actually a ______________. Ø Second, it is the chromosomes that _________________, not individual genes. Ø Alleles of different genes tend to be inherited together when those genes are located on the ______ chromosome.

Lesson Overview Meiosis Gene Mapping Ø In 1911, Columbia University student ______ wondered if the frequency of crossing-over between genes during meiosis might be a clue to the genes’ locations. Ø Sturtevant reasoned that the _____ two genes were on a chromosome, the more likely it would be that a crossover event would occur between them. Ø 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 ___________.

Lesson Overview Meiosis Gene Mapping Ø By this reasoning, he could use the ________ between genes to determine their distances from each other. Ø Sturtevant gathered lab data and presented a _______ showing the relative locations of each known gene on one of the Drosophila chromosomes. Ø Sturtevant’s method has been used to construct gene maps ever since this discovery.