Chapter 13: Meiosis and Sexual Life Cycle

1. Chapter 13: Meiosis and Sexual Life Cycle

2. Background • The passage of genetic information is critical to the reproduction of cells • Genes are segments of DNA representing units of hereditary information • The physical location of a gene on the chromosome is called its locus

3. Types of Reproduction • Asexual reproduction • Single parent cell/organism produces an identical offspring • Except for mutations, the offspring of asexual reproduction are clones of their parents • Sexual reproduction • Results in greater variation in genetic material

4. Two types of cells in humans • Gametes-haploid cells (n), carry one set of chromosomes ex. In humans, an egg (1N) and sperm (1N) are reproductive cells that fuse together creating a diploid zygote • Somatic cells (Diploid cells) carry two sets of chromosomes (2n)

5. In diploid cells, you can pair chromosomes in relation to its size, shape, and banding positions • Karyotyping-arranging chromosomes in relation to number, size, type. • The chromosomes of a pair are called homologous chromosomes • One homologous pair decides your gender • The remaining 22 pairs of chromosomes are called autosomes

6. Significance of homologous pairs? • Their origin! • One member of each homologous pair comes from each parent Ex. Human gametes  haploid cells- single set of chrom (23) • Each parent contributes one set of chromosomes and is a member of each homologous pair. • Fertilization • Egg+ Sperm  Zygote n n 2n

7. How are Gametes Formed? • Meiosis: • Chromosome number is halved by dividing chromosome members of each homologous pair into different gametes • Goes through two rounds of cell division, produces 4 daughter cells w/ half the chromosome number

8. Tetrad-four sister chromatids that pair up Chiasmata-crossing over occurs bwtn nonsister chromatids

10. Mechanisms of genetic variation • Independent assortment • Arrangement of homologous pairs at the metaphase plate in Metaphase I is completely random • Crossing Over • Produces recombinant chromosomes which combine genes inherited from parents • Random Fertilization • Random nature of fertilization that adds to genetic variation

11. Life Cycles • Life cycle- sequence of stages in the reproductive history of an organism • Asexual Life Cycles  bacterium by binary fission

12. Sexual Life Cycles ANIMALS (HUMANS) • Haploid sperm fuses w/ haploid egg  diploid zygote • Zygote grows by mitosis to produce a multicelluar organism

13. Fungi

14. Plants (some algae) • undergo "alternation of generations" where they exist as haploid organisms (gametophytes) and diploid organisms (sporophytes).

15. Extra Stuff

16. Meiosis/mitosis Compared

17. Mechanisms of genetic variation diagram Independent Assortment Crossing Over

18. Vocabulary heredity - the transmission of traits from one generation to the next. variation - offsprings differ somewhat in appearance from parents and siblings. genetics - the scientific study of heredity and hereditary variation. gene pool - the total aggregate of genes in a population at any one time. asexual reproduction - a type of reproduction involving only one parent that produces genetically identical offspring by budding or by the division of a single cell or the entire organism into two or more parts. clone - a lineage of genetically identical individuals. sexual reproduction - a type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from the gametes of the two parents. life cycle - the entire sequence of stages in the life of an organisms, from the adults of one generation to the adults of the next. Somatic cell - any cell in a multicellular organism except a sperm or egg cell. karyotype - a method of organizing the chromosomes of a cell in relation to number, size, and type. homologous chromosomes - chromosome pairs of the same length, centromere position, and staining pattern that possess genes for the same traits at corresponding loci. One homologous chromosome is inherited from the organism's father, the other from the mother. sex chromosomes - the pair of chromosomes responsible for determining the sex of an individual. autosome - a chromosome that is not directly involved in determining sex, as opposed to the sex chromosomes. gamete - a haploid egg or sperm cell; gametes unite during sexual reproduction to produce a diploid zygote. haploid cell -a  cell containing only one set of chromosomes (n).

19. More Vocabulary haploid cell -a  cell containing only one set of chromosomes (n). fertilization - the union of haploid gametes to produce a diploid zygote. zygote - the diploid product of the union of haploid gametes in conception; a fertilized egg. diploid cell - a cell containing two sets of chromosomes (2n), one set inherited from each parent. meiosis - a two-stage type of cell division in sexually reproducing organisms that results in gametes with half the chromosome number of the original cell. alternation of generations - a life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants. sporophyte - the multicellular diploid form in organisms undergoing alternation of generations that results from a union of gametes and that meiotically produces haploid spores that grow into the gametophyte generation. gametophyte- the multicellular haploid form in organisms undergoing alternation of generations, which mitotically produces haploid gametes that unite and grow into the sporophyte generation. meiosis I - first division of cells meiosis II - second meiotic division that separates sister chromatids and is virtually identical in mechanism to mitosis. synapsis - the pairing of replicated homologous chromosomes during prophase I of meiosis. tetrad -chiasma - the X-shaped, microscopically visible region representing homologous chromatids that have exchanged genetic material through crossing over during meiosis. crossing over - the reciprocal exchange of genetic material between nonsister chromatids during synapsis of meiosis I.