Meiosis 5.3

I. Cell Division Replaces worn out or damaged cells Replaces worn out or damaged cells Frequency of division varies by cell type Frequency of division varies by cell type Prokaryotes every 30 minutes Prokaryotes every 30 minutes Nerve cells virtually never Nerve cells virtually never Reproduction depends on cell division Reproduction depends on cell division

II. Two Types of Reproduction Asexual Reproduction Asexual Reproduction reproduction of offspring from one parent reproduction of offspring from one parent offspring have identical genetic material as the parent offspring have identical genetic material as the parent binary fission binary fission a. the simplest form of asexual reproduction b. most common among prokaryotes c. occurs in two stages - copy the single circular DNA molecule - a new cell wall forms between DNA copies

II. Two Types of Reproduction Asexual Reproduction – Binary Fission Asexual Reproduction – Binary Fission

II. Two Types of Reproduction Spores Spores a. a single spore will develop into an adult without combining with another cell b. common among molds and fungi c. important in the life cycle of plants Budding Budding a. a cell’s nucleus divides and the cytoplasm divides unequally b. common among yeasts and simple animals

II. Two Types of Reproduction Vegetative Propagation Vegetative Propagation a. some plants produce organisms that are initially attached to the parent plant b. i.e. strawberry runners (horizontal underground stems) & spider plants Regeneration (fragmentation) Regeneration (fragmentation) a. ability to develop lost body parts or to form new individuals from a single fragment b. i.e. starfish & some plants

II. Two Types of Reproduction Sexual Reproduction Sexual Reproduction formation of a new individual from the union of two specialized parental cells (gemetes) formation of a new individual from the union of two specialized parental cells (gemetes) a. female gamete = ovum or egg b. male gamete = sperm cell always requires TWO parents always requires TWO parents

II. Two Types of Reproduction Sexual Reproduction Sexual Reproduction offspring usually show some characteristics of both parents offspring usually show some characteristics of both parents fertilization – fusion of 2 gametes (1n) (ovum and sperm) to form a zygote (2n) fertilization – fusion of 2 gametes (1n) (ovum and sperm) to form a zygote (2n) zygote – first cell of a new individual zygote – first cell of a new individual

III. DNA and Chromosomes DNA DNA segments of DNA that code for a protein or one RNA molecule is called a gene segments of DNA that code for a protein or one RNA molecule is called a gene one molecule of DNA is made up of 1,000s of genes one molecule of DNA is made up of 1,000s of genes genes determine how a body develops and functions genes determine how a body develops and functions is stretched out while being used is stretched out while being used

III. DNA and Chromosomes Chromosomes Chromosomes is TWO exact copies called chromatids is TWO exact copies called chromatids is made up of DNA wrapped around proteins is made up of DNA wrapped around proteins chromatids are held together at the centromere chromatids are held together at the centromere chromatids separate during cell division chromatids separate during cell division called chromatin when not coiled around proteins called chromatin when not coiled around proteins

III. DNA and Chromosomes Chromosomes Chromosomes

III. DNA and Chromosomes Chromosome Number and Type Chromosome Number and Type Number is different for each type of organism Number is different for each type of organism a. Human – b. Housefly – c. Dog –

III. DNA and Chromosomes Chromosome Number and Type Chromosome Number and Type Number is different for each type of organism Number is different for each type of organism a. Human – 46 b. Housefly – 12 c. Dog – 78 Within an organism; each chromosome is different in size, shape, and set of genes Within an organism; each chromosome is different in size, shape, and set of genes

III. DNA and Chromosomes Chromosome Number and Type Chromosome Number and Type Homologous Chromosomes Homologous Chromosomes a. Pairs of chromosomes that have similar size, shape, & set of genes b. One of the pair comes from one of the two parents c. …..sooooo 46 chromosomes are really two sets of 23 chromosomes; one set from each parent Autosomes Autosomes a. The chromosomes not directly responsible for determining the sex of the individual (22 pair in humans)

III. DNA and Chromosomes Chromosome Number and Type Chromosome Number and Type Sex Chromosomes Sex Chromosomes a. Responsible for determining the sex b. Female = XX c. Male = XY Diploid (2n) Diploid (2n) a. Means two sets of chromosomes b. All cells in your body (somatic cells) except sex cells are diploid Haploid (1n) Haploid (1n) a. Means one set of chromosomes b. Sex cells (gametes) are haploid

III. DNA and Chromosomes Chromosome Number and Type Chromosome Number and Type Karyotype Karyotype a. A photo of a dividing cell that is used to match chromosomes by size and shape b. Matching of chromosomes are used for diagnosis of medical abnormalities c. Trisomy – condition of 3 chromosomes; Down’s syndrome – 3 - #21 chromosome pairs

III. DNA and Chromosomes Karyotype

IV. Meiosis Sex cells (gametes) are formed by this type of nuclear division Sex cells (gametes) are formed by this type of nuclear division Reduces the number of chromosomes to half the number in somatic cells Reduces the number of chromosomes to half the number in somatic cells Somatic cells: Somatic cells: a. 46 chromosomes b. 23 homologous pairs c. diploid number (2n) Gametes Gametes a. 23 chromosomes b. haploid number (1n)

IV. Meiosis Phases in Meiosis Phases in Meiosis Meiosis is preceded by the synthesis of DNA and the replication of the chromosomes. Meiosis is preceded by the synthesis of DNA and the replication of the chromosomes. Has 8 main phases: Has 8 main phases: a. First 4 phases separate homologous chromosomes into 2 different cells b. Last 4 phases separate sister chromatids, just like mitosis

IV. Meiosis Phases in Meiosis Phases in Meiosis Meiosis I Meiosis I a. Phases of Meiosis I i. Prophase I 1. chromosomes become visible 2. the nuclear membrane disappears 3. crossing over occurs * portions of one chromosome are broken and exchanged with the other

IV. Meiosis ii. Metaphase I 1. homologous chromosomes line up along the equator (meet in the middle) iii. Anaphase I 1. homologous chromosomes move to opposite ends of the cell (poles) 2. chromatids DO NOT separate at the centromeres

IV. Meiosis iv. Telophase I 1. chromosomes gather at the poles of the cell 2. cytokinesis takes place and the cell divides into two daughter cells

IV. Meiosis b. At the end of Meiosis I, each daughter cell contains one of each chromosome (half the number) c. Meiosis I is the reductive division; it reduces the number of chromosomes from diploid (2n) to the haploid (1n) number

IV. Meiosis Meiosis II Meiosis II Each daughter cell produced in Meiosis I undergoes another nuclear and cytoplasmic division in Meiosis II Each daughter cell produced in Meiosis I undergoes another nuclear and cytoplasmic division in Meiosis II Meiosis II is similar to Mitosis, but is NOT preceded by the replication of DNA Meiosis II is similar to Mitosis, but is NOT preceded by the replication of DNA

IV. Meiosis Phases of Meiosis II Phases of Meiosis II i. Prophase II 1. telophase I leads directly into prophase II 2. a new spindle forms around the chromosomes

IV. Meiosis ii. Metaphase II 1. chromosomes line up along the cell’s equator 2. spindle fibers attach at the centromere iii. Anaphase II 1. chromosomes separate at the centromere 2. each chromatid in the pair moves to opposite sides of the cell

IV. Meiosis iv. Telophase II 1. nuclear membrane forms around each set of new chromosomes 2. cytokinesis takes place and the cell divides into two daughter cells d. Meiosis II gives four daughter cells that are haploid

IV. Meiosis Meiosis in Males and Females Meiosis in Males and Females Males Males a. results in four cells that differentiate into sperm cells b. Spermatogenesis – the production of sperm cells

IV. Meiosis Meiosis in Males and Females Meiosis in Males and Females Females Females a. Results in four cells; only one of which becomes an ovum b. During Meiosis I, the cytoplasm divides unequally; the smaller cell is called the 1 st polar body c. In Meiosis II, the division is again unequal; the smaller cells die (2 nd polar body)

IV. Meiosis Meiosis in Males and Females Meiosis in Males and Females Females Females d. Because of its larger cytoplasm, the mature ovum has a rich storehouse of nutrients. These nutrients nourish the young organism that may develop if the ovum is fertilized. e. oogenesis – the formation of female egg cells (ovum)

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