2 Two of these people are genetically related, can you tell which two?
3 Section 10.1 - Meiosis Main Idea : Meiosis produces haploid gamates. Meiosis is a type of cell division that reduces the number of chromosomes.46 pairs reduced to 23 pairsA cell with half the number of chromosomes is called haploid. (23 chromosomes n)This type of cell division is important in the life cycle of organisms such as animals.
4 Why is meiosis cell division important? Human body cells have 46 chromosomes.Each parent gives half of their chromosomes (23) to their offspring.The chromosomes that make up apair, one chromosome from eachparent is called ahomologous chromosome.
5 Passing on genetic traits Each chromosomeconsists of hundreds ofgenes.Genes are DNAsegments that carryinstructions for inheritedtraits such as eye color,hair color, and height
6 Examples of Inherited Traits Attached or unattached Can you roll yourearlobes tongue? Some peoplecan’t.
8 How genes are passed from generation to generation Organisms produce gamete cells (sex cells)that have half the number of chromosomes asbody cells. (haploid – n chromosomes)The process of one parent’s gamete combiningwith another parent’s gamete is calledfertilization.
9 Adults have 2n chromosomes (diploid cells – 46 each)If diploid cells fertilized eachother, a cell would end up with92 chromosomes.The next generation wouldhave 184 chromosomes.Eventually there would be toomany chromosomes in eachcell
10 Instead… Animal cells undergo meiosis cell division to reduce the number ofchromosomes beforereproduction occurs.The offspring receives 23chromosomes from thematernal (mother) gamete and23 chromosomes from thepaternal (father) gamete.
11 Meiosis involves two consecutive cell divisions called meiosis I and meiosis II Meiosis I – Reduction StageJust like in mitosis, meiosis cell division beginswith Interphase– cells undergo normalfunctions- DNA replication.
12 Meiosis I – Prophase I Chromatin coils up, Spindles appear, Nucleoli disappear,Synapsis occurs – pairsof homologous chromosomes formHow is this a little different frommitosis prophase?
13 Meiosis IProphase ICrossing over produces exchange of genetic information.Crossing over —chromosomal segments are exchanged between a pair of homologous chromosomes
14 Meiosis I Metaphase I Chromosome centromeres attach to spindle fibers. Homologous chromosomesline up at the equator.How is this different frommitosis metaphase?
15 Meiosis I Anaphase I Homologous chromosomes separate and move to opposite poles of the cell.Centromere not brokenChromosome numberreduced from 2n to nHow is this different frommitosis anaphase?
16 Meiosis I Telophase I The spindles break down. Chromosomes uncoil and form two nucleiThe cell divides,(cytokinesis).Two daughter cellsare produced with ½ thenumber of chromosomes. (n)
17 Meiosis II continues the cell division To begin the second set ofmeiosis stages, we startwith the daughter cellsfrom meiosis I.The DNA will not bereplicated in meiosis II.If we separate the DNA and divide the cells,how many cells will be produced?How many chromosomes in each new cell?
18 Meiosis II – Prophase II A second set of phases begins as the spindleapparatus forms and the chromosomescondense.
19 Meiosis II – Metaphase II A haploid number of chromosomesline up at the equator.
20 Meiosis II – Anaphase II The sister chromatids are pulled apart at thecentromere by spindle fibers and move towardthe opposite poles of the cell.
21 Meiosis II – Telophase II The chromosomes reach the poles, and the nuclear membrane and nuclei reform.
22 Meiosis II - Cytokinesis Cytokinesis results in fourhaploid cells, each withn number of chromosomes.
25 Males – four sperm made by one cell dividing equally into four. MitosisMeiosis IMeiosis II
26 Females – one ovum produced - Unequal division madeduring meiosis I andmeiosis IIOnly the large cellsurvives and is passed onExtra cytoplasmprovides food for the embryo.
27 The Importance of Meiosis I and II Meiosis consists of two sets of divisionsProduces four haploid daughter cells that are not identicalResults in genetic variation
28 Meiosis Provides Variation Depending 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.
29 Studying a person’s genetic make up Every person is madeup of trillions of cells,and each cell carries afull copy of that person’sgenetic code, in the formof homologouschromosomes.
31 Genetic defects – look closely, how are these karyotypes different?
32 Sexual Reproduction vs. Asexual Reproduction the organism inherits allof its chromosomes froma single parent.The new individual isgenetically identical to itsparent.Example – binary fission -- involves an equal division of both the organism cytoplasm and nucleus to form two identical organisms
40 Review of Section 10.1Each student in class has characteristics passed on to them by their parents.The instructions for the traits are found on chromosomes in the nucleus.The DNA on the chromosomes is arranged in segments that control the production of proteinThese DNA segments are called genes.Each chromosome consists of hundreds of genesEach gene has an important role in determining the characteristics and function of the cell
41 10.2 Mendelian Genetics How Genetics Began The passing of traits to the next generation is called inheritance, or heredity.Mendel performed cross-pollination in pea plants.Mendel followed seven traits in the pea plants he bred.Examples: flower color, seed color, height of plant, texture of seed.
43 Mendel’s Experiments – cross-pollination by transferring a male gamete from the flower of one pea plant to the female reproductive organ in a flower of another pea plant.
44 The Inheritance of Traits The parent generation isalso known as the Pgeneration.Cross two pure parentsone yellow & one greenGreen trait didn’tdisappear, it was hiddenor masked.
45 Mendel noticed that some pea plants produce yellow seeds and others produce green. The offspring of this Pcross are called thefirst filial (F1) generation. = __?__All yellowF1 self-pollinates = F2¾ yellow and ¼ greenGreen trait didn’tdisappear, it was hiddenor masked.
46 Genes in Pairs Mendel concluded there must be two forms of the seed trait in the pea plants Allele - An alternative form of a single gene passed from generation to generationThe F1 pea plant had one yellow allele and one green alleleDominant – The allele for yellow seed color is dominant over the green seed color (Y)Recessive – the allele for green seed color is recessive (y)
47 Law of DominanceAn organism with two of the same alleles for a particular trait is homozygousHomozygous yellow –seed plants are YYHomozygous green-seed plants are yyAn organism with two different alleles for a particular trait is heterozygous.= YyWhen alleles are present in the heterozygous state, the dominant trait will be observed.
48 Genotype and Phenotype You cannot tell an organisms alleles by its outward appearance. Some traits may be masked.An organism’s allele pairsare called its genotypeA yellow plant may have agenotype of YY or Yy, bothallele pairs will produceyellow seeds.
49 Mendel’s Law of Segregation Two alleles for each trait separate during meiosis.During fertilization, two alleles for that trait unite.Heterozygous organisms are called hybrids
50 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.
51 Genotype and Phenotype The observable characteristic or outward expression of an allele pair is called the phenotypeThe phenotype of pea plantswith the genotype of yy willbe green seeds.
53 Predicting Genotypes Punnett Squares and Probability Predict the possible offspring of a cross between two known genotypesEach box = 25% chance
54 Monohybrid CrossA cross that involves hybrids for a single trait is called a monohybrid cross.Four boxes in the Punnett square.
55 Dihybrid Cross is for two traits The inheritance of two or more traits in the same plant is a dihybrid cross.Dihybrids are heterozygous for both traits.
56 Punnett Square—Dihybrid Cross Four types of alleles (2 traits) from the male gametes and four types of alleles (2 traits) from the female gametes can be produced.The resulting phenotypic ratio is 9:3:3:1.
57 Cross Test Unknown dominant trait crossed with a known homozygous recessive,If offspring showrecessive phenotype,It is know that the parentwas heterozygous.
58 10.3 Gene Linkage and Polyploidy Genetic Recombination isthe new combination ofgenes produced bycrossing over andindependent assortmentSex Chromosomes =One pairFemale = XX andmale = Xy
59 The X chromosome carries most genes to be passed to offspring. The X chromosome is the largest, Y being the smallest.The X chromosome carries genes needed by both males and femalesThe Y chromosome carries mostly genes for male characteristics.
63 Chromosome Mapping Chromosome mapping = genes in exact locations on all chromosomes withinorganismfarther apart they are morelikely to cross over,so a higher percentage ofcrossed genes would meanthe genes are farther apart
65 After the crossover, A and B are together with c, and a and b are together with C on one of the two chromatids of the recombined chromosomes
66 Polyploidy Polyploidy is the occurrence of one or more extra sets of all chromosomesin an organismA triploid organism, forinstance, would be designated3n, which means that it hasthree complete sets ofchromosomes.Strawberries are 8n
67 In humans, polyploidy is lethal, an embryo will not survive.