Notes – Unit 5 – Biology • Reproduction at the cellular level occurs when one cell called the • Mother Cell divides and forms new cells called the • Daughter Cells • Unicellular organisms which consist of • 1cell, do what by cellular division? • Binary Fission • Multi-cellular organisms which consist of • 2 or more cells, do what by cellular division? • Mitosis • Why must cellular division occur? • So organisms can reproduce, repair, and grow • What do daughter cells receive from the parent cell? • The same DNA
Human bodies rely on cell division to: • 1. Reproduce • 2. Repair • 3. Grow • Bacteria divide every 20 minutes. A human cell divides every • 20 hours.
Reproduction • The production of offspring from one parent is called • Asexual Reproduction • Offspring produced from the union of two special parental cells is • Sexual Reproduction • Asexual Reproduction • Binary Fission Where? • Prokaryotes, Bacteria
Other methods of asexual reproduction • 1. Vegetative Propagation (strawberries) • 2. Regeneration (sea stars) • 3. Budding (Yeast)
IV. The Cell Cycle • The series of changes a cell undergoes from the time it is formed until it reproduces • The cell cycle consists of • Prophase • Metaphase • Anaphase • Telophase
Sexual Reproduction • Sexual reproduction results from the joining of specialized sex cells called • gametes. • The male gamete is called the • sperm. • The female gamete is called the • ovum or egg. • In the process of fertilization, the egg and sperm combine to form the zygote.
Mitosis • Cell division of eukaryotic cells involves… • Mitosis • As a result of mitosis, each daughter cell receives an exact copy of the chromosomes present in the parent cell (the directions). • Each kind of eukaryotic organism has a specific number of chromosomes in its body cells. Body cells are called • Somatic cells. • Humans have 46 chromosomes. Goldfish have 94. Corn plants have 20. Mosquitos have 6! • Cell replication has three main parts… it is called the Cell Cycle • 1. Copy DNA • 2. DNA Divides (Mitosis) • 3. Cell Divides (CYTOKINESIS)
Although the whole cycle may take up to 20 hours, the actual chromosome division is less than 1 hour. The time between divisions is called • INTERPHASE. • What happens during interphase? • 1. Duplicating Cell Material • 2. Cell Grows to nearly double its size • The hereditary material (DNA and Protein) is called • chromatin (tin is very thin) • At the start of the mitosis the chromatin begins to coil up and condense forming short thick rods called • chromosomes. • Each one has two strands called sister chromatids (tids are a chromosomes kids), held together at the centromere (centromere is at the center).
Phases of Mitosis • What happens in prophase? • 1. nuclear membrane disassembled • 2. nucleolus seems to disappear • 3. chromatin is packaged as (becomes) chromosomes • 4. spindle apparatus (only fibers in plants) begins to form
Protein tubes called spindle fibers form between the centrioles. These with additional tubules form the aster. • The function of the aster is unknown. Many plant cells have spindle fibers but not centrioles and asters.
II. Metaphase • What happens in metaphase (middlephase!)? • 1. Chromosomes attach to the spindle fibers (apparatus in animals) • 2. Chromosome align along equator (middle) • This is the best place to study chromosomes. Why? • Chromosomes are visible and lined up in the middle.
III. Anaphase • What happens in anaphase? • 1. Centromeres separate (sister chromatids become 2 chromosomes!) • 2. Microtubules (spindle fibers) shorten • 3. Chromosomes are pulled towards the poles
IV. Telophase • What happens in telophase? • 1. Chromosomes reach poles • 2. Nuclear membrane reforms • 3. Nucleolus reappears • 4. Chromosomes de-condense
Cytokinesis • Begins during …Telophase • In animal cells the cell membrane pinches inward and together. In plant cells a cell plate must be formed first which is produced by the Golgi Bodies.
Eukaryotic Cell Cycle -Stages • Interphase (3 parts) – cell spends most of time growing and protein synthesis • G1 Phase – Growth 1 - Cell grows does “daily activities” • S Phase – Synthesis -DNA is copied • G2 Phase – Growth 2- Organelles are copied • M Phase – Mitosis - Chromosomes are separated into the 2 ends of the cell, each pole will become a new cell that is exactly the same as the old • C Phase – Cytokinesis – Cytoplasm divides and 2 identical daughter cells are formed
Prophase – • DNA constricts into chromosomes • Nuclear membrane disappears Metaphase • Chromosomes align in the middle of the cell Anaphase • Chromosomes are pulled apart to opposite sides of the cell and form halves called • Sister Chromatids
Telophase, the final stage of mitosis • Begins when chromosomes have completed their migration • Nuclear membrane reforms • Chromosomes begin to unwind back into chromatin Cytokinesis – begins when the Cell membrane divides and a ring pinches the two cells apart
MEIOSIS • All cells produced through mitosis have the same number of chromosomes as their parent cell. • What would happen if two mitotic cells combined in sexual reproduction? • In humans this would result in a cell with 92 chromosomes! • It would no longer be human. It would be an Aquatic Rat
How many chromosomes would the daughter cells have? 92 Chromosomes in somatic cells occur in pairs called homologs. Humans have 46 chromosomes with 23 pairs of homologs. This is said to be diploid which means there are 23 sets of homologous pairs (2n). A gamete has only one member of each pair (half the diploid number). A human gamete (egg and sperm) has only 23 chromosomes and is said to be haploid (n) “half loid”.
Meiosis reduces the number of chromosomes to half the number in somatic cells. This process requires two successive cell divisions. • Meiosis I (reduction division) • Meiosis II
MEIOSIS I • Preceded by the synthesis of DNA and replication of the chromosomes (Interphase?). • Homologous chromosomes come together – process is called • Pairing Chromosomes • Chromosomes lie next to each other forming a • tetrad. • What happens?
Prophase I Crossing Over Metaphase I Chromosomes Cross Over genetic information Chromosomes line up in middle of cell
Anaphase I Telophase I Haploid Chromosomes move to poles of cell: Cytokinesis occurs Chromosomes are pulled apart by spindle fibers
Meiosis I is the “reduction division”. It reduces the number of chromosomes from the diploid (2n) to the haploid (n) number.
MEIOSIS II • Meiosis II is similar to mitosis but is not preceded by the replication of DNA (no Interphase!)
Prophase II Metaphase II Haploid Chromosomes line up in the middle of the cells Chromosomes stay condensed: But do not replicate again!!!
Each of the daughter cells produced in meiosis II is haploid. Meiosis in male cells results in four cells that differentiate or change into gametes (sperm). Meiosis in female cells results in only one viable egg cell as the cytoplasm divides unequally.
Fundamentals of Genetics • The passing of traits from parents to offspring is called • Heredity. • The scientific study of heredity is called • Genetics. Traits are transmitted by means of Chromatin Network: (rod-shaped structures within the nucleus) • Units of heredity are called • Genes • Gregor Mendel July 22, 1822 (monk and teacher) experiments with • Pea Plants
Mendel did experiments using The Stamen and Pistol (gametes). When peas fertilize themselves it is called Self Pollination. After many generations, offspring are genetically identical and have the same traits.
Mendel’s Experiments • Mendel cross-pollinated pea plants • Focused his work on 7 different traits seed color: yellow vs. green seed shape: smooth vs. wrinkled pod color: green vs. yellow pod shape: inflated vs. pinched stem height: tall vs. short flower position: axial vs. terminal flower/seed coat color: purple vs. white flowers grey vs. white seed coats Counted the offspring of each phenotype and analyzed the results mathematically
Mendel crossed two pure breeding plants. The parent plants were called the Parental (P) generation. He performed Cross Pollination in order to mix the genes. The results and first generation was the 1st Filial Generation or F1 Generation (Offspring of Parental Generation After testing all of the traits, Mendel discovered that one trait in each pair showed up in the F1 generation. The other trait seemed to disappear. Next he allowed the F1 to self pollinate, producing the F2 generation. Ratio Tall: Short = 3:1 How would you explain this?
MENDEL’s PrinciplesThe Principle of Dominance • The principle of dominance states that one factor (gene) in a pair may prevent the other factor (gene) in the pair from being expressed. • A gene that masks the other gene in a pair is called • The Dominant Gene. • The gene that is hidden in the F1 generation is called • The Recessive Gene. • Geneticists use the following symbols: • Dominant – Capital Letter • Recessive – Lower case letter
When the two genes are identical the individual is said to be • Homozygous • When the two genes are both dominant it is • Homozygous Dominant (Represented by two Capital Letters. BB) • Individuals with a dominant gene and a recessive are • Heterozygous (One Capital and one lower case letter. Bb) • The Principle of Segregation • The principle of segregation states that the members of each pair of genes separate, or segregate, when gametes are formed. • When does this happen? • Anaphase II of Meiosis • Draw this phase of the cell cycle.
Principle of Independent Assortment • The principle in independent assortment states that two or more pairs of genes segregate independently of one another during the formation of gametes. However, these genes need to be on different chromosomes. Mendel was lucky since the traits he found in peas were on different chromosomes. • A term used to refer to either member of a pair of genes is • Alleles • The pairs of alleles in the cells of an organism make up • Genotype • A trait that is actually expressed in an organism’s appears is the • Phenotype
The PunnettSquare • A grid, or chart which shows all the possible gene combinations for a cross (male is traditionally across the top and female is on the left side. • Draw a punnett square of the following cross: • Male: Brown Eyes (BB) x Female Brown Eyes (Bb)
Crosses involving one trait are called • Monohybrid crosses. • Crosses Involving Two Traits are called • Dihybrid crosses. • A cross involving two pairs of alleles is called a • Dihybrid cross. (This is proof of Independent Assortment.
Incomplete Dominance • Not all phenotypes result from dominant and recessive genes • Here both alleles are expressed. • Example • Manx cat – homozygous for no tail (NN) • Normal Cat – homozygous for long tail (LL) • Cross a normal with a Manx cat in a Punnet square and then list the phenotypes and genotypes:
Try this one: • Red Morning Glory (RR) • White Morning Glory (WW) • Cross a white and a red morning glory.