Glencoe Biology

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Section 1 Meiosis
Section 2 Mendelian Genetics
Section 3 Gene Linkage and Polyploidy
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Chromosomes and Chromosome Number

• Human body cells have 46 chromosomes

• Each parent contributes 23 chromosomes

• Homologous chromosomesone of two paired
  chromosomes, one from each parent

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Chromosomes and Chromosome Number

• Same length

• Same centromere position

• Carry genes that control the same inherited traits

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Haploid and Diploid Cells

• An organism produces gametes to maintain the same
  number of chromosomes from generation to
  generation.

• Human gametes contain 23 chromosomes.

• A cell with n chromosomes is called a haploid
  cell. A single set of chromosomes (half the full
  set of genetic material)

• A cell that contains 2n chromosomes is called a
  diploid cell. A cell that has two sets of
  chromosomes one set from the father and one from
  the mother.

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• The sexual life cycle in animals involves meiosis.

• Meiosis produces gametes.

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Stages of Meiosis I

• Reduces the chromosome number by half through the
  separation of homologous chromosomes

• Involves two consecutive cell divisions called
  meiosis I and meiosis II
• PMAT I and PMAT II

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• Interphase

• Chromosomes replicate.

• Chromatin condenses.

Interphase
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• Prophase I

• Pairing of homologous chromosomes occurs.

• Each chromosome consists of two chromatids.

Prophase I

• The nuclear envelope breaks down.

• Spindles form.

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• Prophase I

• Crossing over produces exchange of genetic
  information.

• Crossing overchromosomal segments are exchanged
  between a pair of homologous chromosomes.

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• Metaphase I

• Chromosome centromeres attach to spindle fibers.

Metaphase I

• Homologous chromosomes line up at the equator.

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• Anaphase I

Anaphase I
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis I

• Telophase I

• The spindles break down.

Telophase I

• Chromosomes uncoil and form two nuclei.

• The cell divides.

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis II

• Prophase II

Prophase II
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis II

• Metaphase II

Metaphase II
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis II

• Anaphase II

Anaphase II
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis II

• Telophase II

Telophase II
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Meiosis II

• Cytokinesis results in four haploid cells, each
  with n number of chromosomes.

Cytokinesis
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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis

• How to tell which process (mitosis, meiosis I, or
  meiosis II)?
• Look at how the chromosomes are lined up?

a. PAIRS.must be Meiosis I b. SINGLE
FILEMitosis or Meiosis II

• Look at the chromosome number
• is HAPLOID must be Meiosis II
• is DIPLOID must be Mitosis

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
The Importance of Meiosis

• Meiosis consists of two sets of divisions

• Produces four haploid daughter cells that are not
  identical

• Results in genetic variation

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
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.

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Sexual Reproduction and Genetics
Chapter 10
10.1 Meiosis
Sexual Reproduction v. Asexual Reproduction

• Asexual reproduction

• The organism inherits all of its chromosomes from
  a single parent.

• The new individual is genetically identical to
  its parent.

• Sexual reproduction

• Beneficial genes multiply faster over time.

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
How Genetics Began

• Gregor Mendel was curious of why some pea plants
  had different physical characteristics (traits).
  Why they looked different?
• He observed that the pea plants' traits were
  often similar to those of their parents,
  sometimes they were different.
• The passing of traits to the next generation is
  called inheritance, or heredity.

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10.2 Mendelian Genetics

• He used pea plants because they have many traits
  that exist in only two forms. (tall/short, green
  seed/yellow seed) and they were self pollinating
• He decided to cross plants with opposite forms of
  a trait, for example, tall plants and short
  plants.

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics

• The parent generation is also known as the P
  generation.

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics

• 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.

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics

• Mendel studied seven different traits.

• Seed or pea color

• Flower color

• Seed pod color

• Seed shape or texture

• Seed pod shape

• Stem length

• Flower position

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10.2 Mendelian Genetics

• Some of the traits

Pod color
Seed Color
Plant Height
Green
Yellow
Green
Yellow
Seed Shape
Pod Shape
Short
Tall
Round
Wrinkled
Smooth
Pinched
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10.2 Mendelian Genetics

• MENDEL CONCLUDED
• individual factors must control the inheritance
  of traits in peas.
• They exist in pairs and the female parent
  contributes one factor while the male parent
  contributes the other.

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10.2 Mendelian Genetics

• Today we call those factors that control traits
  genes.
• They call the different forms of gene alleles.
• Although his work was not recognized until much
  later, Mendel is known as the father of genetics
  for his experiments and papers about his pea
  plants.

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Genes in Pairs

• Allele

• An alternative form of a single gene passed from
  generation to generation

• Dominant

Usually we represent these types of traits with
letters (TT, Tt, tt)

• Recessive

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Dominance

• An organism with two of the same alleles for a
  particular trait is homozygous.

• An organism with two different alleles for a
  particular trait is heterozygous.

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Genotype and Phenotype

• An organisms allele pairs are called its
  genotype. (Ex BB, Bb, bb)

• The observable characteristic or outward
  expression of an allele pair is called the
  phenotype. (Ex blue eyes, blonde hair, etc.)

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Punnett Squares

• Predict the possible offspring of a cross between
  two known genotypes

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Monohybrid Cross

• A cross that involves hybrids for a single trait
  is called a monohybrid cross.

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics

• Monohybrid Cross
• Punnett square
• Punnett squares can be used to determine the
  probability of getting a certain trait
• Remember that results predicted by probability
  are more likely to be seen when there is a large
  number of offspring

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Mendels Law of Segregation

• Mendels first law, the Law of Segregation, has
  three parts. From his experiments, Mendel
  concluded that

1. Plant traits are handed down through
hereditary factors in the sperm and egg.
2. Because offspring obtain hereditary factors
from both parents, each plant must contain two
factors for every trait.
3. The factors in a pair segregate (separate)
during the formation of sex cells, and each sperm
or egg receives only one member of the pair.
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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Mendels Law of Segregation

• Two alleles for each trait separate during
  meiosis.

• During fertilization, two alleles for that trait
  unite.

• Heterozygous organisms are called hybrids.

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Dihybrid Cross

• The simultaneous inheritance of two or more
  traits in the same plant is a dihybrid cross.

• Dihybrids are heterozygous for both traits.

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Punnett SquareDihybrid 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.

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Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
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.

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Genetic Recombination Genetic Disorders
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Genetic Recombination

• The new combination of genes produced by crossing
  over and independent assortment

• Combinations of genes can be calculated using the
  formula 2n, where n is the number of chromosome
  pairs.

• Humans have 23 pairs of chromosomes, so 223 over
  8 million now when fertilization occurs, 223x
  223 70 trillionno wonder each individual is
  unique!

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Polyploidy
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Alterations of Chromosome Structure

• Breakage of a chromosome can lead to four types
  of changes in chromosome structure
• Deletion
• Duplication
• Inversion
• Translocation

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• A deletion- lose chromosome fragment
• A duplication- extra segment of chromosome
  attaches to a sister chromatid.

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• An inversion chromosome segment in reverse
  orientation.
• In translocation, a chromosomal fragment joins a
  nonhomologous chromosome.

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Nondisjunction
Results in chromosomal error in which one or more
chromosomes have extra or missing copies
ANEUPLOIDY Cell with only 1 copy of a
chromosome instead of 2 MONOSOMY Cell with 3
copies of a chromosome instead of 2 TRISOMY