Binary fission occurs in prokaryotes. parent cell. DNA duplicates. cell begins to divide. daughter cells

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4 Some eukaryotes reproduce through mitosis. Binary fission is similar in function to mitosis. Asexual reproduction is the creation of offspring from a single parent. Binary fission produces two daughter cells genetically identical to the parent cell. parent cell Binary fission occurs in prokaryotes. DNA duplicates cell begins to divide daughter cells

5 Budding forms a new organism from a small projection growing on the surface of the parent. Hydra bud Yeast

6 Fragmentation is the splitting of the parent into pieces that each grow into a new organism. Vegetative reproduction forms a new plant from the modification of a stem or underground structure on the parent plant. Sea Stars

7 Parthenogenesis - female makes fertile egg (lizard, snake, cricket) (Biology Letters, DOI: /rsbl ).

8 Benefits of Asexual Reproduction No energy wasted on making gametes. No energy wasted on finding a mate. Faster, more efficient.

9 All offspring are identical and have identical weaknesses. If environment changes, all may die.

10 Two parents give DNA to offspring Zygote = union of 2 gametes (sex cells) by fertilization Most eukaryotes reproduce sexually

11 Increases variation through: Crossing over: exchange of genetic material between homologous chromosomes Independent assortment: random distribution of homologous chromosomes during meiosis. Random fertilization: egg and sperm meet randomly

12 Why is variety good? If the environment changes, some of the offspring might survive if they have different traits that are useful.

13 Spend energy making gametes Spend energy finding a mate Takes more time to do these things

14 Environment determines what form of reproduction is most advantageous. Asexual reproduction is an advantage in consistently favorable conditions. Sexual reproduction is an advantage in changing conditions.

15 Let s Compare Sexual and Asexual Reproduction: Benefits Sexual Reproduction Asexual Reproduction Costs

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17 If a new human is created from the union of two cells (one from the father and mother) How do you avoid doubling the chromosome number each time? sperm (father) egg (mother) zygote (cell)

18 Human - 23 pair (23 from each parent) Fruit fly - 8 pair Garden pea - 14 pair Recall that each chromosome contains thousands of genes that determine different traits

19 The Genetic material (chromosomes) come in pairs. HOMOLOGOUS chromosomes are chromosomes that carry the same information on them Example: hair color One of the homologous chromosomes may carry the information for blonde hair and another for brown hair.

20 Your cells have autosomes and sex chromosomes. Your body cells have 23 pairs of chromosomes. Homologous pairs of chromosomes have the same structure. For each homologous pair, one chromosome comes from each parent. Chromosome pairs 1-22 are autosomes. Sex chromosomes, X and Y, determine gender in mammals.

21 An arrangement of photographs of chromosomes in order from largest to smallest using a stained chromosome spread.

22 Body cells are diploid; gametes are haploid. Fertilization between egg and sperm occurs in sexual reproduction. Diploid (2n) cells have two copies of every chromosome. Body cells are diploid. Half the chromosomes come from each parent.

23 How can you avoid doubling your chromosome number each time? Each sperm & egg contain half (n) the number of chromosomes of all other cells! sperm (father) 23 egg (mother) 46 zygote (cell) So, when 2 gametes join, the zygote has the correct number (2n) of chromosomes.

24 Haploid (n) cells have one copy of every chromosome. Gametes are haploid. Gametes have 22 autosomes and 1 sex chromosome.

25 Diploid cells are cells that have two of each chromosome. Most of the cells that make up your body are diploid. Haploid cells are cells that have only one of each chromosome. Female egg cells and male sperm cells are haploid cells When one haploid gamete combines with another haploid gamete its called fertilization.

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28 KEY CONCEPT Gametes have half the number of chromosomes that body cells have. You have body cells and gametes. Body cells are also called somatic cells. Germ cells develop into gametes. Germ cells are located in the ovaries and testes. Gametes are sex cells: egg and sperm. Gametes have DNA that can be passed to offspring. body cells sex cells (sperm) sex cells (egg)

29 Chromosome number must be maintained in animals. Many plants have more than two copies of each chromosome. Mitosis and meiosis are types of nuclear division that make different types of cells. Mitosis makes more diploid cells.

30 Meiosis makes haploid cells from diploid cells. Meiosis occurs in sex cells. Meiosis produces gametes.

31 KEY CONCEPT During meiosis, diploid cells undergo two cell divisions that result in haploid cells. Meiosis reduces chromosome number and creates genetic diversity.

32 Meiosis I and meiosis II each have four phases, similar to those in mitosis. Pairs of homologous chromosomes separate in meiosis I. Homologous chromosomes are similar but not identical. Sister chromatids divide in meiosis II. Sister chromatids are copies of the same chromosome. homologous chromosomes sister chromatids sister chromatids

33 Meiosis I occurs after DNA has been replicated. Meiosis I divides homologous chromosomes in four phases.

34 Homologous chromosomes exchange sections of DNA in a process is called crossing over during Prophase I

35 Meiosis II divides sister chromatids in four phases. DNA is not replicated between meiosis I and meiosis II.

36 Meiosis differs from mitosis in significant ways. Meiosis has two cell divisions while mitosis has one. In mitosis, homologous chromosomes never pair up. Meiosis results in haploid cells; mitosis results in diploid cells.

37 Why don t you and your siblings look exactly the same? Because not all of the gametes that a person makes are identical.

38 1. Random Fertilization Egg and sperm meet randomly! 2 23 X 2 23 or 70 trillion different combinations!!! That s a lot of variety!

39 Chromosomes from mom and dad don t always end up on the same side during metaphase II, they have independent assortment

40 homologous chromosomes exchange sections of DNA in a process is called crossing over during Prophase I

41 Type of cell # of chromosomes (n) Gametes (sex cells) Somatic cells (all other cells) Come from # of cells from one parent cell Process Purpose # of divisions Genetic info

42 Type of cell Gametes (Sex Cells) Somatic cells (all other cells) # of chromosomes n haploid 2n diploid Come from Germ cells Somatic cells # of cells from parent cell 4 sperm or 1 egg Process meiosis mitosis Purpose Reproduction All other # of divisions 2 1 Genetic info Shuffled around identical 2

43 Meiosis vs. Mitosis Meiosis Occurs in two phases: Meiosis I Meiosis II Genetic information is shuffled around. Results in four different haploid daughter cells Occurs in sex cells Mitosis Occurs in one phase. Genetic information remains the same. Results in two identical diploid daughter cells. Occurs in somatic cells

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46 All the events in the growth and development to maturity of an organism Diploid Life cycle: multicellular organism is diploid, haploid stage is single cell gamete. (animals) Haploid Life cycle: multicellular organism is haploid, diploid stage is single cell. (fungi, some protists)

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