Cells reproduce by cell division One cell gives

§ Cells reproduce by cell division. • One cell gives rise to two or more cells, called daughter cells. (Virchow) • Each daughter cell receives a complete set of heredity information—identical to the information in the parent cell—and about half of the cytoplasm. Copyright © 2009 Pearson Education Inc.

§ Cell division transmits hereditary information to each daughter cell. • The hereditary information in each cell is deoxyribonucleic acid (DNA). • DNA is contained in chromosomes. • A molecule of DNA consists of smaller subunits called nucleotides. Copyright © 2009 Pearson Education Inc.

§ The eukaryotic chromosome consists of DNA bound to protein. • Human chromosomes contain a single DNA double helix that is 50 to 250 million nucleotides long, which would be about 3 inches long if the DNA were completely relaxed. Copyright © 2009 Pearson Education Inc.

§ The nucleotides are held together by hydrogen bonding between the bases in two strands, called a double helix, which looks like a twisted ladder. James Watson and Francis Crick combined the X-ray data with bonding theory to deduce the structure of DNA Copyright © 2009 Pearson Education Inc.

DNA is composed of four nucleotides DNA is made of chains of small subunits called nucleotides Each nucleotide has three components 1. A phosphate group 2. A deoxyribose sugar 3. One of four nitrogen-containing bases 1. Thymine (T) 2. Cytosine (C) 3. Adenine (A) 4. Guanine (G) Copyright © 2009 Pearson Education Inc.

§ The structure of DNA phosphate nucleotide base T A sugar C G G

Hydrogen bonds between complementary bases hold two DNA strands together in a double helix (continued) Because of their structures and the way they face each other, adenine (A) bonds only with thymine (T) and guanine (G) bonds only with cytosine (C) Bases that bond with each other are called complementary base pairs Thus, if one strand has the base sequence CGTTTAGCCC, the other strand must have the sequence GCAAATCGGG Copyright © 2009 Pearson Education Inc.

Parental DNA double helix The parental DNA is unwound New DNA strands are synthesized with bases complementary to the parental strands Each new double helix is composed of one parental strand (blue) and one new strand (red) Copyright © 2009 Pearson Education Inc.

§ Segments of different lengths along a DNA molecule are the units of inheritance called genes. § Each gene spells out the instructions for making the proteins of the cell. § When a cell divides, it first replicates its DNA, and each copy is transferred into each daughter cell. Copyright © 2009 Pearson Education Inc.

a pair of homologous chromosomes Both chromosomes carry the same allele of the gene at this locus; the organism is homozygous at this locus gene loci This locus contains another gene for which the organism is homozygous Each chromosome carries a different allele of this gene, so the organism is heterozygous at this locus the chromosome from the male parent Copyright © 2009 Pearson Education Inc. the chromosome from the female parent

• Homologous chromosomes carry the same kinds of genes for the same characteristics • Genes for the same characteristic are found at the same loci on both homologous chromosomes • Genes for a characteristic found on homologous chromosomes may not be identical • Alternative versions of genes found at the same gene locus are called alleles Copyright © 2009 Pearson Education Inc.

a pair of homologous chromosomes Both chromosomes carry the same allele of the gene at this locus; the organism is homozygous at this locus gene loci This locus contains another gene for which the organism is homozygous Each chromosome carries a different allele of this gene, so the organism is heterozygous at this locus the chromosome from the male parent Copyright © 2009 Pearson Education Inc. the chromosome from the female parent

§ An organism’s two alleles may be the same or different • Each cell carries two alleles per characteristic, one on each of the two homologous chromosomes • If both homologous chromosomes carry the same allele (gene form) at a given gene locus, the organism is homozygous at that locus • If two homologous chromosomes carry different alleles at a given locus, the organism is heterozygous at that locus (a hybrid) Copyright © 2009 Pearson Education Inc.

a pair of homologous chromosomes Both chromosomes carry the same allele of the gene at this locus; the organism is homozygous at this locus gene loci This locus contains another gene for which the organism is homozygous Each chromosome carries a different allele of this gene, so the organism is heterozygous at this locus the chromosome from the male parent Copyright © 2009 Pearson Education Inc. the chromosome from the female parent

§ The number of different types of chromosomes in a species is called the haploid number and is designated n. • In humans, n = 23. § Diploid cells contain 2 n chromosomes. • Humans body cells contain 2 n = 46 (2 x 23) chromosomes. Copyright © 2009 Pearson Education Inc.

§ A typical human cell has 23 pairs of chromosomes. § 22 of these pairs have a similar appearance and are called autosomes. § Human cells also have a pair of sex chromosomes, which differ from each other in appearance and in genetic composition. • Females have two X chromosomes. • Males have one X and one Y chromosome. Copyright © 2009 Pearson Education Inc.

§ Eukaryotic chromosomes usually occur in pairs. • An entire set of stained chromosomes

§ Cell division is required for growth and development. • Cell division in which the daughter cells are genetically identical to the parent cell is called Mitotic cell division. • After cell division, the daughter cells may grow and divide again, or may differentiate, becoming specialized for specific functions. • The repeating pattern of division, growth, and differentiation followed again by division is called the cell cycle. Copyright © 2009 Pearson Education Inc.

§ Duplicated chromosomes separate during cell division. • Prior to cell division, the DNA within each chromosome is replicated. • The duplicated chromosomes then consist of two DNA double helixes and associated proteins that are attached to each other at the centromere. Copyright © 2009 Pearson Education Inc.

§ Duplicated chromosomes separate during cell division (continued). • Each of the duplicated chromosomes attached at the centromere is called a sister chromatid. • During mitotic cell division, the sister chromatids separate and each becomes a separate chromosome that is delivered to one of the two resulting daughter cells. Copyright © 2009 Pearson Education Inc.

§ Eukaryotic chromosomes during cell division centromere genes duplicated sister chromosome chromatids (2 DNA double helices) (a) A replicated chromosome consists of two sister chromatids independent daughter chromosomes, each with one identical DNA double helix (b) Sister chromatids separate during cell division Copyright © 2009 Pearson Education Inc. Fig. 8 -5

Eukaryotic cell cycle Copyright © 2009 Pearson Education Inc.

§ There are two types of division in Eukarytic cells: mitotic cell division and meiotic cell division. • Mitotic cell division may be thought of as ordinary cell division, such as occurs during development from a fertilized egg, during asexual reproduction, and in skin, liver, and the digestive tract every day. • Meiotic cell division is a specialized type of cell division required for sexual reproduction. Copyright © 2009 Pearson Education Inc.

Meiotic cell division Meiosis Copyright © 2009 Pearson Education Inc.

§ Cell division is required for sexual and asexual reproduction. • Sexual reproduction in eukaryotic organisms occurs when offspring are produced by the fusion of gametes (sperm and eggs) from two adults. • Gametes are produced by meiotic cell division, (Meiosis which results in daughter cells with exactly half of the genetic information of their parent cells). • Fertilization of an egg by a sperm results in the restoration of the full complement of hereditary information in the offspring. Copyright © 2009 Pearson Education Inc.

Mitotic cell division Mitosis Copyright © 2009 Pearson Education Inc.

§ Reproduction in which offspring are formed from a single parent, without having a sperm fertilize an egg, is called asexual reproduction. • Asexual reproduction produces offspring that are genetically identical to the parent. • Examples of asexual reproduction occur in bacteria, single-celled eukaryotic organisms, multicellular organisms such as Hydra, and many trees, plants, and fungi. Copyright © 2009 Pearson Education Inc.

§ The eukaryotic cell cycle is divided into two major phases: interphase and cell division. • During interphase, the cell acquires nutrients from its environment, grows, and duplicates its chromosomes. • During cell division, one copy of each chromosome and half of the cytoplasm are parceled out into each of two daughter cells. Copyright © 2009 Pearson Education Inc.

§ Mitotic cell division • Mitotic cell division consists of nuclear division (called mitosis) followed by cytoplasmic division (called cytokinesis) and the formation of two daughter cells. Copyright © 2009 Pearson Education Inc.

§ Mitosis is divided into four phases. • • Prophase Metaphase Anaphase Telophase Copyright

§ Prophase Copyright © 2009 Pearson Education Inc. Fig. 8 -9 b–c

§ During prophase, the chromosomes condense and are captured by the spindle microtubules. § Three major events happen in prophase: • The duplicated chromosomes condense. • The spindle microtubules form. • The chromosomes are captured by the spindle. Copyright © 2009 Pearson Education Inc.

§ The centriole pairs migrate with the spindle poles to opposite sides of the nucleus. • When the cell divides, each daughter cell receives a centriole. § Every sister chromatid has a structure called a kinetochore located at the centromere, which attaches to a spindle apparatus. Copyright © 2009 Pearson Education Inc.

§ Metaphase Copyright © 2009 Pearson Education Inc. Fig. 8 -9 d

§ During metaphase, the chromosomes line up along the equator of the cell. • At this phase, the spindle apparatus lines up the sister chromatids at the equator, with one kinetochore facing each cell pole. Copyright © 2009 Pearson Education Inc.

§ Anaphase Copyright © 2009 Pearson Education Inc. Fig. 8 -9 e

§ During anaphase, sister chromatids separate and move to opposite poles of the cell. • Sister chromatids separate, becoming independent daughter chromosomes. • The kinetochores pull the chromosomes poleward along the spindle microtubules. Copyright © 2009 Pearson Education Inc.

§ Telophase Copyright © 2009 Pearson Education Inc. Fig. 8 -9 f

§ During telophase, nuclear envelopes form around both groups of chromosomes. • Telophase begins when the chromosomes reach the poles. • The spindle microtubules disintegrate and the nuclear envelop forms around each group of chromosomes. Copyright © 2009 Pearson Education Inc.

§ Cytokinesis Copyright © 2009 Pearson Education Inc. Fig. 8 -9 g

§ Cytokinesis occurs during telophase, separating each daughter nucleus into a separate cell that

§ During cytokinesis, the cytoplasm is divided between two daughter cells. Microfilaments form a ring around the cell’s equator. The microfilament ring contracts, pinching in the cell’s “waist. ” (a) Microfilaments contract, pinching the cell in two Copyright © 2009 Pearson Education Inc. The waist completely pinches off, forming two daughter cells (b) Scanning electron micrograph of cytokinesis. Fig. 8 -10

§ Cytokinesis in plant cells is different than in animal cells. • In plants, carbohydrate-filled vesicles bud off the Golgi apparatus and line up along the cell’s equator between the two nuclei. • The vesicles fuse, forming a cell plate. • The carbohydrate in the vesicles become the cell wall between the two daughter cells. Copyright © 2009 Pearson Education Inc.

Prokaryotic cell cycle Copyright © 2009 Pearson Education Inc.

§ The prokaryotic cell cycle consists of a long period of growth, during which the cell duplicates its DNA. cell division by binary fission cell growth and DNA replication (a) The prokaryotic cell cycle Copyright © 2009 Pearson Education Inc. Fig. 8 -3 a

1. Binary fission occurs among prokaryotes (cells that do not contain a nucleus). 2. Mitosis occurs among eukaryotes (cells that have a nucleus). 3. Binary fission does not include spindle formation (mitotic apparatus) and sister chromatids in its process making it a faster means of cellular division than mitosis. 4. Binary fission does not have the four distinct cellular phases (from G 1 down to the final mitotic phase) that are seen in mitosis. Copyright © 2009 Pearson Education Inc.

10. 1 What Is the Physical Basis of Inheritance? § Inheritance is the process

10. 1 What Is the Physical Basis of Inheritance? • A gene is a unit of heredity that encodes information needed to produce proteins, cells, and entire organisms • Genes comprise segments of DNA ranging from a few hundred to many thousands of nucleotides in length • The location of a gene on a chromosome is called its locus (plural, loci) Copyright © 2009 Pearson Education Inc.

• Homologous chromosomes carry the same kinds of genes for the same characteristics • Genes for the same characteristic are found at the same loci on both homologous chromosomes o. However genes for a characteristic found on homologous chromosomes may not be identical • Alternative versions of genes found at the same gene locus are called alleles Copyright © 2009 Pearson Education Inc.

§ An organism’s two alleles may be the same or different • Each cell carries two alleles per characteristic, one on each of the two homologous chromosomes • If both homologous chromosomes carry the same allele (gene form) at a given gene locus, the organism is homozygous at that locus • If two homologous chromosomes carry different alleles at a given locus, the organism is heterozygous at that locus (a hybrid) Copyright © 2009 Pearson Education Inc.

§ Mutations are the source of alleles • Alleles arise as mutations—changes in the nucleotide sequence in genes • If a mutation occurs in a cell that becomes a sperm or egg, it can be passed on from parent to offspring • Most mutations occurring in the DNA of an organism initially appeared in the reproductive cells Copyright © 2009 Pearson Education Inc.

§ Gregor Mendel, an Austrian monk, discovered the common patterns of inheritance and many essential facts about genes, alleles, and the distribution of alleles in gametes and zygotes during sexual reproduction § He chose the edible pea plant for his experiments, which took place in the monastery garden • Because of their structure, pea flowers naturally selffertilize • Pollen from the stamen of a plant transfers to the carpel of the same plant, where the sperm then fertilizes the plant’s eggs Copyright © 2009 Pearson Education Inc.

• Mendel was able to mate two different plants by hand (cross-fertilization) • Female parts (carpels) were dusted with pollen from other selected plants • Unlike previous researchers, Mendel chose a simple experimental design • He chose to study individual characteristics (called traits) that had unmistakably different forms, such as white versus purple flowers • He started out by studying only one trait at a time Copyright © 2009 Pearson Education Inc.

10. 3 How Are Single Traits Inherited? § True-breeding organisms possess traits that remain inherited unchanged by all offspring produced by selffertilization § Mendel’s cross-fertilization of pea plants used true-breeding organisms § Mendel cross-fertilized true-breeding, white-flowered plants with true-breeding, purple-flowered plants • The parents used in a cross are part of the parental generation (known as P) • The offspring of the P generation are members of the first filial generation (F 1) • Offspring of the F 1 generation are members of the F 2 generation Copyright © 2009 Pearson Education Inc.

Figure 10 -4 Cross of pea plants true-breeding for white or purple flowers pollen Parental generation (P) pollen cross-fertilize true-breeding, purple-flowered plant true-breeding, white-flowered plant First-generation offspring (F 1) all purple-flowered plant Copyright © 2009 Pearson Education Inc.

10. 3 How Are Single Traits Inherited? § Mendel’s flower color experiments • Mendel allowed the F 1 generation to self-fertilize • The F 2 was composed of 3/4 purple-flowered plants and 1/4 white-flowered plants, a ratio of 3: 1 • The results showed that the white trait had not disappeared in the F 1 but merely was hidden • Mendel then self-fertilized the F 2 generation • In the F 3 generation, all the white-flowered F 2 plants produced white-flowered offspring • These proved to be true-breeding Copyright © 2009 Pearson Education Inc.

Figure 10 -5 Self-fertilization of F 1 pea plants with purple flowers Firstgeneration offspring (F 1) self-fertilize Secondgeneration offspring (F 2) 3/4 purple Copyright © 2009 Pearson Education Inc. 1/4 white

10. 3 How Are Single Traits Inherited? § In the F 3 generation, self-fertilized purple-flowered F 2 plants produced two types of offspring • About 1/3 were true-breeding for purple • The other 2/3 were hybrids that produced both purple - and white-flowered offspring, again, in the ratio of 3 purple to 1 white • Therefore, the F 2 generation included 1/4 truebreeding purple-flowered plants, 1/2 hybrid purple, and 1/4 true-breeding white-flowered plants Copyright © 2009 Pearson Education Inc.

• There are two alleles for a given gene characteristic (such as flower color) • Let P stand for the dominant purple-flowered allele: A homozygous purple-colored plant has two alleles for purple flower color (PP) and produces only P gametes • Let p stand for the recessive white-flowered allele: A homozygous white-colored plant has two alleles for white flower color (pp) and produces only p gametes Copyright © 2009 Pearson Education Inc.

• The particular combination of the two alleles carried by an individual is called the genotype • For example, PP or Pp • The physical expression of the genotype is known as the phenotype (for example, purple or white flowers) Copyright © 2009 Pearson Education Inc.

• A cross between a purple-flowered plant (PP) and a white-flowered plant (pp) produces all purple-flowered F 1 offspring, with a Pp genotype • Dominant P gametes from purple-flowered plants combined with recessive p gametes from white-flowered plants to produce hybrid purpleflowered plants (Pp) Copyright © 2009 Pearson Education Inc.

§ Simple “genetic bookkeeping” can predict genotypes and phenotypes of offspring • The Punnett square method predicts offspring genotypes and phenotypes from combinations of parental gametes 1. First, assign letters to the different alleles of the characteristic under consideration (uppercase for dominant, lowercase for recessive) 2. Determine the gametes and their fractional proportions (out of all the gametes) from both parents Copyright © 2009 Pearson Education Inc.

$3. Write the gametes from each parent, together with their fractional proportions, along each$

3. Write the gametes from each parent, together with their fractional proportions, along each side of a 2 x 2 grid (Punnett square) 4. Fill in the genotypes of each pair of combined gametes in the grid, including the product of the fractions of each gamete (e. g. , 1/4 PP, 1/4 Pp and 1/4 p. P, and 1/4 pp) 5. Add together the fractions of any genotypes of the same kind (1/4 Pp + 1/4 p. P = 1/2 Pp total) Copyright © 2009 Pearson Education Inc.

6. From the sums of all the different kinds of offspring genotypes, create a genotypic fraction • 1/4 PP, 1/2 Pp, 1/4 pp is in the ratio 1 PP : 2 Pp : 1 pp 7. Based on dominant and recessive rules, determine the phenotypic fraction • A genotypic ratio of 1 PP : 2 Pp : 1 pp yields 3 purple-flowered plants : 1 whiteflowered plant Copyright © 2009 Pearson Education Inc.

Figure 10 -8 Determining the outcome of a single-trait cross Pp self-fertilize P p eggs sperm eggs offspring genotypes genotypic ratio (1: 2: 1) phenotypic ratio (3: 1) sperm P PP P p Pp PP Pp purple Pp p p. P pp Punnett square of a single-trait cross Copyright © 2009 Pearson Education Inc. p P p p pp pp white Using probabilities to determine the offspring of a single-trait cross