sexual reproduction and genetics
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Sexual Reproduction and Genetics. Chapter 10. http://main.uab.edu/cord/show.asp?durki=38593. Meiosis 10.1. Chromosomes. Human body cells have 46 chromosomes. Each parent contributes 23 chromosomes resulting in 23 pairs. - PowerPoint PPT PresentationTRANSCRIPT
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Sexual Reproductionand Genetics
Chapter 10http://main.uab.edu/cord/show.asp?durki=38593
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Meiosis10.1
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• Human body cells have 46 chromosomes. Each parent contributes 23 chromosomes resulting in 23 pairs.
• The chromosomes that make up a pair (one chromosome from each parent) are called homologous chromosomes.
• Homologous chromosomes have the same length and centromere position and they carry genes that control the same traits.
Chromosomes
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Chromosomes
http://www.phschool.com/science/biology_place/labbench/lab3/homologs.html
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Chromosome Number• To maintain the same chromosome
number from generation to generation, organisms produce gametes.
• Gametes: sex cells that have half the number of chromosomes.
• The symbol n is used to represent the number of chromosomes in a gamete.
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Chromosome Number• An organism with n number of
chromosomes is called a haploid cell.
• Fertilization: the process by which one haploid gamete combines with another haploid gamete.
• As a result of fertilization the cell will now contain a total of 2n chromosomes (n from the female parent and n from the male parent).
• An organism with 2n chromosomes is called a diploid cell.
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Chromosome Number
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Asexual vs Sexual Reproduction
• Asexual Reproduction: only one parent, offspring identical to parent.
• Sexual Reproduction: two parents combine their genetic material to produce offspring that are genetically different from both parents.
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Mitosis vs Meiosis
• Mitosis maintains the chromosome number.
• Meiosis reduces the chromosome number by half.
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Mitosis vs Meiosis
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Meiosis
• Meiosis: cell division resulting in a reduced number of chromosomes, gamete formation.
• Occurs in the reproductive structures of organisms that reproduce sexually.
• Involves two cell divisions called Meiosis I and Meiosis II.
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Sexual Life Cycle
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Meiosis I• Chromosome pairs replicate resulting in
two haploid (n) daughter cells with duplicated chromosomes different from the sets in the original diploid (2n) cell.
• Occurs in 4 stages: prophase I, metaphase I, anaphase I, and telophase I.
• Begins with interphase, like in mitosis. Cells increase in size, produce RNA, synthesize proteins, and replicate DNA.
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Meiosis I
http://kenpitts.net/hbio/8cell_repro/meiosis_pics.htm
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Meiosis I: Prophase I• Replicated chromosomes become
visible.
• Pairing of homologous chromosomes occurs, each chromosome consists of two chromatids.
• Crossing over: chromosomal segments are exchanged between a pair of homologous chromosomes producing an exchange of genetic information.
• Nuclear envelope breaks down and spindles form.
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Meiosis I: Prophase I
http://www.biology.iupui.edu/biocourses/N100/2k2ch9meiosis.html
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Meiosis I: Metaphase I
• Chromosome centromeres attach to the spindle fibers.
• Homologous chromosomes line up at the equator.
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Meiosis I: Metaphase I
http://www.biology.iupui.edu/biocourses/N100/2k2ch9meiosis.html
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Meiosis I: Anaphase I
• Homologous chromosomes separate and move to the opposite poles of the cell.
• Sister chromatids remain attached.
• Each daughter cell will receive only one chromosome from each homologous pair.
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Meiosis I: Anaphase I
http://www.biology.iupui.edu/biocourses/N100/2k2ch9meiosis.html
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Meiosis I: Telophase I
• The spindles begin to break down.
• Chromosomes uncoil and form two nuclei.
• The cell divides.
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Meiosis I: Telophase I
http://www.phschool.com/science/biology_place/biocoach/meiosis/teloi.html
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Meiosis II
• Each of the two daughter cells from Meiosis I contains only one chromosome from each parental pair.
• Each daughter cell from Meiosis I will undergo Meiosis II.
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Meiosis II
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Meiosis II: Prophase II
• The chromosomes condense and the spindles form in each new cell.
• The spindle fibers attach to the chromosomes.
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Meiosis II: Prophase II
http://www.phschool.com/science/biology_place/biocoach/meiosis/teloi.html
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Meiosis II: Metaphase II
• The centromeres of chromosomes line up randomly at the equator of each cell.
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Meiosis II: Metaphase II
http://www.phschool.com/science/biology_place/biocoach/meiosis/teloi.html
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Meiosis II: Anaphase II
• The centromeres split.
• The sister chromatids separate and move to opposite poles.
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Meiosis II: Telophase II
• Four nuclei form around chromosomes.
• The spindle fibers begin to break down.
• The cell divides.
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Anaphase II & TelophaseII
http://www.biology.iupui.edu/biocourses/N100/2k2ch9meiosis.html
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Meiosis
http://www.daviddarling.info/encyclopedia/M/meiosis.html
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Mendelian Genetics10.2
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How Genetics Began
• Inheritance: the passing of traits to the next generation.
• Gregor Mendel: published findings on the method and mathematics of inheritance in garden pea plants.
http://www.scienceclarified.com/scitech/Genetics/The-Age-of-Genetics.html
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Why Pea Plants?
• Pea plants are easy to grow and many are true-breeding which means they consistently produce offspring with only on form of a trait.
• Pea plants usually reproduce by self-fertilization (male and female gametes in same flower).
• Pea plants can easily be cross-pollinated by hand (transferring a male or female gamete in one flower to another flower).
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Pea Plants
http://www.exploringnature.org/db/detail.php?dbID=22&detID=54
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The Inheritance of Traits• Mendel noticed certain varieties of garden
pea plants produced specific forms of a trait, generation after generation.
• Mendel performed cross pollination by transferring male gametes from the flower of a true-breeding green-seed plant to the female organs of a flower from a true-breeding yellow-seed plant.
• Mendel called the green-seed plants and the yellow-seed plants the parent generation or P generation.
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The Inheritance of Traits
• When Mendel grew the seeds from the cross between the green-seed and yellow-seed plants, all of the offspring had yellow seeds.
• The offspring of the P cross are called the first filial (F1) generation.
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The Inheritance of Traits
• Mendel then planted the F1 generation of yellow seeds to determine whether the green-seed trait was no longer present or if it was being masked.
• The results of the second filial (F2) generation are as follows: 6022 were yellow and 2001 were green (a nearly perfect 3:1 ratio of yellow to green seeds).
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Inheritance of Traits
• Mendel studied seven different traits, including: seed or pea color, flower color, seed pod color, seed shape or texture, seed pod shape, stem length, and flower positions.
• He found that the F1 generation plants from these crosses also showed a 3:1 ratio.
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F1 and F2 Generations
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Genes in Pairs• From his experiments, Mendel
concluded that there must be two forms of the seed trait in the pea plants and that each was controlled by a factor.
• Allele: an alternative form of a single gene passed from generation to generation.
• The green-seed and yellow-seed are different forms of a single gene or alleles.
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Genes in Pairs
• Mendel called the form of the trait that appeared in the F1 generation dominant and the form that was masked recessive.
• The yellow-seed was dominant and the green-seed was recessive.
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Law of Dominance• If the allele for a trait is dominant it is
represented by a capital letter. In Mendel’s case the yellow-seeds were dominant and therefore represented by a Y.
• If the allele for a trait is recessive it is represented by a lowercase letter. Therefore the green-seeds in Mendel’s experiment would be represented by a y.
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Law of Dominance
• An organism with two of the same alleles for a particular trait is homozygous.
• Homozygous yellow-seed plants would be YY and homozygous green-seed plants would be yy.
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Law of Dominance• Heterozygous organisms have two
different alleles for a trait.
• In Mendel’s experiment a plant with an allele for yellow-seeds and green-seeds would be represented by Yy.
• When an organism is heterozygous the dominant allele will be expressed.
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Genotype and Phenotype
• Genotype: an organism’s allele pairs.
• The genotype of a plant with yellow seeds would be YY or Yy.
• Phenotype: the observable characteristics or outward expression of allele pair.
• The phenotype of pea plants with the genotype yy would be green seeds.
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Genotype and Phenotype
http://hthbio.blogspot.com/2011/02/february-7-2011-february-11-2011.html
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Law of Segregation
• Two alleles for each trait separate during meiosis and during fertilization two alleles for that trait unite.
http://www.transtutors.com/homework-help/Biology/Heredity/mendel-experiment-of-monohybrid-ratio.aspx
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Law of Independent Assortment
• A random distribution of alleles occurs during gamete formation.
• Genes on separate chromosomes separate independently during meiosis.
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http://bio1152.nicerweb.net/Locked/media/ch14/assortment.html
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Punnett Squares
• Used to predict the possible offspring of a cross between two known genotypes.
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Monohybrid Cross
• Examines the inheritance of one trait.
• Parent generation could both be homozygous or heterozygous or one could be homozygous and the other heterozygous.
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Monohybrid Cross
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Dihybrid Cross
• Examines the inheritance of two different traits.
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Dihybrid Crossry ry ry ry
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
R = dominant round, r = recessive wrinkled; Y = dominant for yellow, y = recessive green (rryy x RRYY)
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Gene Linkage and Polyploidy
10.3
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Genetic Recombination
• The new combination of genes produced by crossing over and independent assortment.
• The possible combination of genes due to independent assortment can be calculated by the formula 2n where n is the number of chromosomes.
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Gene Linkage
• Linked genes are genes that are located close to each other on the same chromosomes.
• These genes tend to travel together during gamete formation.
• Linked genes do not segregate independently and are therefore an exception to Mendel’s Law of Independent Assortment.
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Chromosome Maps• Chromosome Maps: drawings that show
the sequence of genes on a chromosome and represent the relative position of genes.
• The higher the crossover frequency, the farther apart the two genes are because crossing over occurs more frequently between genes that are far apart.
• The frequency correlates with the relative distance between the two genes.
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Chromosome Maps
https://wikispaces.psu.edu/display/Bio110nk/Chromosome+Behavior+and+Gene+Linkage
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Polyploidy
• Polyploidy: the occurrence of one or more extra sets of chromosomes in an organism.
• Ex) 3n: 3 complete sets of chromosomes.
• Rarely occur in animals but sometimes occur in earthworms and goldfish.
• Approximately 1 in 3 species of flowering plants are polyploid.
• Polyploidy is always lethal in humans.
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Polyploidy
8n