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Chapter 10 Sexual Reproduction and Genetics

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Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis – PowerPoint PPT presentation

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Title: Chapter 10 Sexual Reproduction and Genetics


1
Chapter 10 Sexual Reproduction and Genetics
  • 10.1 Meiosis

2
Chromosomes and Chromosome Number
  • Human body cells have 46 chromosomes
  • DNA on the chromosomes are arranged in sections
    that code for a trait these sections are genes
  • Humans have approximately 23,000 genes

3
Chromosomes and Chromosome Number
  • Of the 46 human chromosomes each parent
    contributes 23 chromosomes
  • These chromosomes are paired
  • Homologous chromosomesone of two paired
    chromosomes, one from each parent

4
Homologous Chromosomes
  • Same centromere position
  • Same length
  • Homologous 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
    (ditwo)

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 cells
  • Fertilization 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 animals
  • Most plants
  • Most fungi
  • Most protists

9
Meiosis I and Meiosis II
  • Meiosis I is the reduction division cells start
    out diploid and end up haploid
  • In Meiosis II sister chromatids are separated
    (much like mitosis)

10
Meiosis I
  • Interphase
  • Chromosomes replicate.
  • Chromatin condenses.

Interphase
11
Meiosis I
  • Prophase I
  • Pairing of homologous chromosomes occurs.
  • Each chromosome consists of two chromatids.

Prophase I
  • The nuclear envelope breaks down.
  • Spindles form.

12
Meiosis I
  • Prophase I
  • Crossing over produces exchange of genetic
    information.
  • Crossing overchromosomal segments are exchanged
    between a pair of homologous chromosomes.

Tetrads are groups of four sister chromatids
13
Meiosis I
  • Metaphase I
  • Chromosomes centromere attach to spindle fibers.

Metaphase I
  • Homologous chromosomes line up at the equator in
    tetrads

14
Meiosis I
  • Anaphase I

Anaphase I
15
Meiosis I
  • Telophase I
  • The spindles break down.

Telophase I
  • Chromosomes uncoil and form two nuclei.
  • The cell divides.

16
Meiosis II
  • Prophase II

Prophase II
17
Meiosis II
  • Metaphase II

Metaphase II
18
Meiosis II
  • Anaphase II

Anaphase II
19
Meiosis II
  • Telophase II

Telophase II
20
Meiosis II
  • Cytokinesis 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
    identical
  • Results in genetic variation

22
Meiosis
  • 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.

23
Meiosis and Variation
  • Number of possible genetic variations in the
    gametes equals
  • 2n where n is the haploid number
  • In humans number of possible genetic combinations
    in gametes is 223
  • Add 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 gamete
  • When fertilization occurs this number must be
    doubled 2 x (223)3
  • You 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 Mendel
  • Lived in Europe in what is now Czech Republic
    near the Austrian border.
  • Father of Genetics
  • Monk, entered monastery 1843

29
Gregor Mendel
  • Failed teachers exam
  • When to U of Vienna
  • Studied with physicist Doppler- science through
    experiment, applied math to science
  • Studied with botanist Unger- interest in causes
    of variation in plants
  • Passed teachers exam and taught at monasterys
    school also responsible for schools garden
  • Published 1866, mathematics and plant breeding

30
Mendel Studied Peas
  • Available in many varieties
  • Self pollinating (can manipulate pollination)
  • either-or inherited traits
  • Had true breeder for parental generation (P)
    due to flower structure

31
Mendel Studied Peas
  • The petals enclose the stamen (with pollen) so
    that cross pollination does not occur
  • Cross pollination is easily accomplished by
    peeling back the petals and moving pollen with a
    paint brush

32
Inheritance of Traits
33
Inheritance of Traits
  • The offspring of this P cross are called the
    first filial (F1) generation.
  • The second filial (F2) generation is the
    offspring from the F1 cross.

34
Pea Traits Studied by Mendel
35
Inheritance of Traits
  • Mendel studied thousand of pea plants for the
    seven traits.
  • He concluded that
  • Genes are in pairs
  • Different versions of genes (alleles) account for
    variation in inherited characteristics
  • Alleles 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.

37
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38
Symbols
  • To help make genetics easier symbols are used
  • Capital letters are used for dominant alleles
  • Lower case letters are used for recessive alleles
  • The letter to use is based on the dominant trait
  • Example 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 heterozygous
  • Homo same the alleles would be the same, PP
  • Heterodifferent the alleles would be different,
    Pp
  • For 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
    pp
  • Phenotype 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 pp
  • If the phenotype displays the dominant trait
    (purple) then the genotype could be homozygous
    dominant (PP) or heterozygous (Pp)

Genotype is PP or Pp
Genotype is pp
42
Punnett Squares
  • Mathematical device for predicting the results of
    genetic cross
  • Male gametes are written across the top
  • Female gametes are written along the side
  • Genetic possibilities of the offspring are in the
    boxes
  • Expect 31 phenotypic ratio

43
Monohybrid Cross
  • Mono one
  • One trait is studied at a time
  • This one is seed color
  • Monohybrid crosses provided evidence for the Law
    of Segregation

44
Mendels 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 Cross
  • Four types of alleles from the male gametes and
    four types of alleles from the female gametes can
    be produced.
  • The resulting phenotypic ratio is 9331 which
    gave evidence for the Law of Independent
    Assortment

47
Mendels Law of Independent Assortment
  • Random distribution of alleles occurs during
    gamete formation
  • Genes on separate chromosomes sort independently
    during meiosis.
  • Each allele combination is equally likely to
    occur.

48
Mendels Law of Independent Assortment
49
Probability
  • Genetic 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 Linkage
  • The linkage of genes on a chromosome results in
    an exception to Mendels law of independent
    assortment because linked genes usually do not
    segregate independently.

52
Polyploidy
  • Polyploidy is the occurrence of one or more extra
    sets of all chromosomes in an organism.
  • Approximately 30 of flowers are polyploidy
  • Strawberries are octoploidy (8n)

53
Polyploidy
  • Horticultural 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.
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