Presentation on theme: "Chapter 10 Sexual Reproduction and Genetics"— Presentation transcript:
1 Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis
2 Chromosomes and Chromosome Number Human body cells have 46 chromosomesDNA on the chromosomes are arranged in sections that code for a trait; these sections are genesHumans have approximately 23,000 genes
3 Chromosomes and Chromosome Number Of the 46 human chromosomes each parent contributes 23 chromosomesThese chromosomes are pairedHomologous chromosomes—one of two paired chromosomes, one from each parent
4 Homologous Chromosomes Same centromere positionSame lengthHomologous chromosomes contain the same genes; although they may contain different versions of the gene
5 Chromosomes and Chromosome Number Haploid cells contain only one of the homologous pair of chromosomes (half the number of chromosomes)Diploid cell contain the chromosomes in pairs (di=two)
6 Chromosomes and Chromosome Number Gametes (sex cells) contain the haploid number of chromosomes (n)Body cells contain the diploid number of chromosomes (2n)Human gametes (sperm and egg) have 23 chromosomes and body cells have 46 chromosomes
7 Meiosis Gametes are formed during the process of meiosis Meiosis reduces diploid cells to haploid cellsFertilization restores the diploid number
8 Meiosis Meiosis involves two consecutive sets of cell divisions Meiosis only occurs in the reproductive structures of organisms who reproduce sexually:Most animalsMost plantsMost fungiMost protists
9 Meiosis I and Meiosis II Meiosis I is the reduction division; cells start out diploid and end up haploidIn Meiosis II sister chromatids are separated (much like mitosis)
10 Meiosis I Interphase Chromosomes replicate. Chromatin condenses.
11 Meiosis I Prophase I Pairing of homologous chromosomes occurs. Each chromosome consists of two chromatids.Prophase IThe nuclear envelope breaks down.Spindles form.
12 Meiosis IProphase ICrossing over produces exchange of genetic information.Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes.Tetrads are groups of four sister chromatids
13 Meiosis IMetaphase IChromosome’s centromere attach to spindle fibers.Metaphase IHomologous chromosomes line up at the equator in tetrads
14 Meiosis I Anaphase I Homologous chromosomes separate and move to opposite poles of the cell.Anaphase I
15 Meiosis I Telophase I The spindles break down. Chromosomes uncoil and form two nuclei.The cell divides.
16 Meiosis II Prophase II A second set of phases begins as the spindle apparatus forms and thechromosomes condense.Prophase II
17 Meiosis II Metaphase II A haploid number of chromosomes line up at the equator.Metaphase II
18 Meiosis II Anaphase II The sister chromatids are pulled apart at the centromere by spindlefibers and move toward the opposite polesof the cell.Anaphase II
19 Meiosis II Telophase II The chromosomes reach the poles, and the nuclear membrane and nuclei reform.Telophase II
20 Meiosis IICytokinesis results in four haploid cells, each with n number of chromosomes.Cytokinesis
21 Meiosis Meiosis consists of two sets of divisions Produces four haploid daughter cells that are not identicalResults in genetic variation
22 MeiosisDepending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result.Genetic variation also is produced during crossing over and during fertilization, when gametes randomly combine.
23 Meiosis and VariationNumber of possible genetic variations in the gametes equals:2n where n is the haploid numberIn humans number of possible genetic combinations in gametes is 223Add the genetic combinations that exist when crossing over exists (at 3 per meiosis) and get (223)3
24 Meiosis and Variation, cont The possibility that (223)3 variations exists for each gameteWhen fertilization occurs this number must be doubled 2 x (223)3You are unique; no one else exists or ever has existed that is just like you (unless you have an identical twin).
25 Advantages of Asexual Reproduction The organism inherits all of its chromosomes from a single parent.The new individual is genetically identical to its parent.Usually occurs more rapidly than sexual reproduction
26 Advantages of Sexual Reproduction Beneficial genes multiply faster over time.The organisms inherits genes from two parents and is not genetically identical to either parent.Ensures genetic variation
27 Chapter 10 Sexual Reproduction and Genetics 10.2 Mendelian Genetics
28 Gregor MendelLived in Europe in what is now Czech Republic near the Austrian border.Father of GeneticsMonk, entered monastery 1843
29 Gregor Mendel Failed teacher’s exam When to U of Vienna Studied with physicist Doppler- science through experiment, applied math to scienceStudied with botanist Unger- interest in causes of variation in plantsPassed teacher’s exam and taught at monastery’s school; also responsible for school’s gardenPublished 1866, mathematics and plant breeding
30 Mendel Studied Peas Available in many varieties Self pollinating (can manipulate pollination)“either-or” inherited traitsHad “true breeder” for parental generation (P) due to flower structure
31 Mendel Studied PeasThe petals enclose the stamen (with pollen) so that cross pollination does not occurCross pollination is easily accomplished by peeling back the petals and moving pollen with a paint brush
35 Inheritance of TraitsMendel studied thousand of pea plants for the seven traits.He concluded that:Genes are in pairsDifferent versions of genes (alleles) account for variation in inherited characteristicsAlleles can be dominant or recessive
36 Dominant and Recessive Alleles can be dominant or recessive.An allele is dominant if it appears in the F1 generation when true breeder parents are crossed.An allele is recessive if it is masked in the F1 generation.
38 Symbols To help make genetics easier symbols are used Capital letters are used for dominant allelesLower case letters are used for recessive allelesThe letter to use is based on the dominant traitExample: purple is dominant to white, P would be the dominant allele and p the recessive allele
39 Homozygous and Heterozygous Dominant traits can be homozygous or heterozygousHomo= same; the alleles would be the same, PPHetero=different; the alleles would be different, PpFor the recessive trait to be expressed both alleles would be recessive, pp
40 Genotype and Phenotype Genotype is the organism's gene pairs: PP, Pp or ppPhenotype is the outward physical appearance or expression of the genotype: purple or white
41 Genotype and Phenotype If the phenotype displays the recessive trait (white) then you know the genotype; ppIf the phenotype displays the dominant trait (purple) then the genotype could be homozygous dominant (PP) or heterozygous (Pp)Genotype is PP or PpGenotype is pp
42 Punnett SquaresMathematical device for predicting the results of genetic crossMale gametes are written across the topFemale gametes are written along the sideGenetic possibilities of the offspring are in the boxesExpect 3:1 phenotypic ratio
43 Monohybrid Cross Mono= one One trait is studied at a time This one is seed colorMonohybrid crosses provided evidence for the Law of Segregation
44 Mendel’s Law of Segregation Two alleles for each trait separate during meiosis
45 Dihybrid Cross Di= two Two traits are studied at a time This one is seed color (yellow or green) and seed shape (wrinkled or round)
46 Dihybrid CrossFour types of alleles from the male gametes and four types of alleles from the female gametes can be produced.The resulting phenotypic ratio is 9:3:3:1 which gave evidence for the Law of Independent Assortment
47 Mendel’s Law of Independent Assortment Random distribution of alleles occurs during gamete formationGenes on separate chromosomes sort independently during meiosis.Each allele combination is equally likely to occur.
49 ProbabilityGenetic crosses predict what to expect in the phenotypes and genotypes of the offspring.Observed results are what you actually see with the organisms.The larger the number of offspring the closer the expected and observed results usually are.
50 Chapter 10 Sexual Reproduction and Genetics 10.3 Gene Linkage and Polyploidy
51 Gene LinkageThe linkage of genes on a chromosome results in an exception to Mendel’s law of independent assortment because linked genes usually do not segregate independently.
52 PolyploidyPolyploidy is the occurrence of one or more extra sets of all chromosomes in an organism.Approximately 30% of flowers are polyploidyStrawberries are octoploidy (8n)
53 PolyploidyHorticultural important plants are forced to polyploidy to increase the size and flavor of flowers and fruits and overall vigor of the plants.Polyploidy is uncommon in animals.