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Basic Principles of Inheritance

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Gamete formation. Grows into plant. P. P. p. p. p. P. FERTILIZATION. Pp ... or segregated in the formation of gametes (eggs and sperm), then unite at radom ... – PowerPoint PPT presentation

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Title: Basic Principles of Inheritance


1
Basic Principles of Inheritance
Principle of Segregation
2
Inheritance The first hunch
  • Why do children look like their parents?
  • The male contributes the most to offspring
    features homunculus inside the sperm
  • Qualities of the parents blended to form the
    qualities of the child

3
Gregor Mendel (1822-1884)
4
3 basic questions
  • What is inherited?
  • How is it inherited?
  • What is the role of chance in heredity?

5
Mendels observations
  • Variation, expressed in alternative forms of a
    trait, is widespread in nature.
  • ? basis for evolution
  • Observable variation is essential for following
    the distribution of traits in the offspring

6
Mendels observations
7
Mendels observations
  • Traits dissapeared in one generation and
    reapeared in another generation of inbred plants.
  • Variation seems not to be distributed by chance

8
Hypothesis
  • Observable traits are determined by independent
    units of inheritance
  • A particle with no physical feature whose
    function is to control a visible trait
  • Today GENE
  • Region of DNA that encodes a specific proteinor
    a particular type of RNA

9
The Mendelian Experiments
  • Isolation of pure- breeding lines
  • Generation of hybrids
  • Control over fertilization allowing reciprocal
    crosses

10
Mendels PeasThese are the seven
characteristics, each having two contrasting
traits, that Mendel identified.
11
Mendels Experiments
  • He experimentally crosses different strains of
    pure plants (parental generation) to develop
    hybrids (F1 generation).
  • He then crossed these hybrids (F1 gen.) and
    analyzed the results (F2 gen.)

12
Mendels Results
  • The hybrids (F1 gen.) only displayed one of the
    parental traits. (tall)
  • When crossing two hybrids, some of the resulting
    offspring (F2 gen.) displayed one of the parental
    traits and some displayed the other. (some tall
    some short)
  • These traits in the F2 generation consistently
    occurred in a 3 to 1 ratio. (3 tall 1short)

13
Mendelian Laws
  • Principle of Segregation
  • Mendel's Principle of Independent Assortment

14
Principle of Segregation
  • Monohybrid crossing
  • Evidence that blending did not occur
  • Yellow-pea hybrids should have the information to
    produce green peas

15
Principle of Segregation
P
Grows into plant
Gamete formation
P
PP
p
Grows into plant
Gamete formation
p
pp
p
Seed formation
FERTILIZATION
Pp
P
Pp
16
Principle of Segregation
  • The factors of inheritance (genes) come in
    alternative forms (alleles)
  • The 2 alleles for each trait are separated or
    segregated in the formation of gametes (eggs and
    sperm), then unite at radom one from each parent
    during fertilization.

17
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18
Definitions
  • DNA Deoxyribonucleic acid the molecule in which
    genetic information is encoded.
  • Allele One alternative of a pair or group of
    genes that could occupy a specific position on a
    chromosome.
  • Chromosome A linear strand of DNA harboring many
    genes.
  • Gene A unit of genetic information that occupies
    a specific position on a chromosome and comes in
    multiple versions called alleles.
  • Genotype The genetic constitution of an
    organism.
  • Phenotype The physical or observable
    characteristics of an organism.

19
Definitions
  • Heterozygous Having a genotype with two
    different and distinct alleles for the same
    trait.
  • Homozygous Having a genotype with two of the
    same alleles for a trait.
  • Dominant An allele producing the same phenotypic
    effect whether inherited heterozygously or
    homozygously an allele that "masks" a recessive
    allele.
  • Recessive An allele producing no phenotypic
    effect when inherited heterozygously and only
    affecting the phenotype when inherited
    homozygously an allele "masked" by a dominant
    allele.

20
Mendelian Laws
  • Principle of Segregation
  • Mendel's Principle of Independent Assortment

21
Principle of segregation
  • For any particular trait, the pair of alleles of
    each parent separate and only one allele passes
    from each parent on to an offspring.  Which
    allele in a parent's pair of alleles is inherited
    is a matter of chance.  We now know that this
    segregation of alleles occurs during the process
    of meiosis

22
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23
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24
Principle of Independent Assortment
  • Different pairs of alleles are passed to
    offspring independently of each other.  The
    result is that new combinations of genes present
    in neither parent are possible

25
  • Inheritance of Bood Types
  • 1 gene
  • 3 alleles (A,B,i)
  • Possible Genotypes

26
Remember
  • GENE
  • Nucleic acid (DNA) segments that determine a
    specific characteristic
  • LOCUS
  • Localization of a gene in a chromosome
  • Singular locus/ PluralLoci
  • ALLELE
  • Diferent forms of a gene
  • MUTATION
  • Change in the DNA sequence
  • KARYOTYPE
  • the chromosomal constitution of the cell nucleus
    by extension, the microphotograph of chromosomes
    arranged.

27
Gene, locus y allele
  • Genes
  • A,B,C
  • Alleles
  • Gene A A1, A2
  • Gene B B1
  • Gene C C3, C1
  • Locus
  • Gene A
  • Gene B
  • Gene C

A
A1 B1 C3
A2 B1 C1
B
C
CROMOSOME 5
28
DEFINITIONS
LOCUS Physical site occupied by a gene. EXAMPLE
Angiotensin 1q42 43
29
Definitions
1
  • Autosomic Trait
  • Inherited characteristic whose allele is is
    present in the chromosomes different from X and Y
    (autosomic)
  • In humans pair 1 to 22

23
22
30
  • Trait linked to sex
  • Inherited characteristic whose allele is is
    present in the X or Y chromosomes (pair 23 in
    humans XX o XY)

31
Paterns of inheritance
  • Autosomic dominant
  • Phenotype is determined by dominant allele and
    present in all sexes
  • Autosomic Recessive
  • Phenotype is determined by recesive allele and
    present only in homozygous state
  • Linked to sex
  • Only present in one sex

32
Generation of variability
  • During Metaphase I crossing-over results in a
    physical exchange of equivalent segments of
    chromosomes
  • If there are allelic differences between these
    segments, then the products of crossing-over are
    genetic recombinants for those alleles

33
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