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Patterns of Inheritance


Patterns of Inheritance Chapter 10 – PowerPoint PPT presentation

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Title: Patterns of Inheritance

Patterns of Inheritance
  • Chapter 10

Blending Hypothesis of Inheritance
  • Trait
  • A variation of a particular characteristic
  • Blending hypothesis (1800s)
  • Early explanation of how offspring inherit trait
    from both parents
  • Example if a red flower plant crossed with a
    yellow flower, the offspring would be orange
  • Later discarded

Gregor Mendel
  • Austrian monk
  • Father of Genetics (study of heredity)
  • Said parents pass on to their offspring separate
    and distinct genes
  • Studied 7 characteristics in pea plants

  • True breeding plants
  • A true plant will show the same physical
    appearance generation after generation after
  • Cross fertilization
  • The sperm from the pollen of one true flower
    fertilizes the eggs in the flower of a different

Mendel's Experiments
  • Cross-fertilized 2 true-breeding plants each with
    contrasting traits (i.e. white and purple
  • What color of flowers do you think the offspring
    plants were?

Principle of Segregation
  • P generation
  • Parental plants (purebred and true breeding)
  • F1 generation ( F for filial son)
  • Hybrid offspring
  • Hybrids
  • The offspring of 2 different true-breeding
  • F2 generation
  • When F1 self-fertilize or fertilize each other

Monohybrid Cross
  • Monohybrid cross
  • Cross fertilization in which only one physical
    characteristic is considered
  • In Mendel's cross, all F1 were purple but ¼ of F2
    were white

Gene Hypotheses 1
  • There are alternative forms of genes which
    determine physical appearances
  • Allele is the term
  • Example Flower color can be white or purple

Gene Hypotheses 2
  • For each characteristic, an organism has 2
    alleles for genes controlling the physical
    appearances (one from each parent)
  • If 2 alleles are the same homozygous
  • If 2 alleles are different heterozygous

Gene Hypotheses 3
  • Dominant alleles determine the physical
    appearance in a heterozygous individual.
  • Recessive allele is the other allele that does
    not affect the physical appearance
  • Capital letter represents dominant allele P
  • Lower case letter represents recessive allele p

  • Phenotype is the physical appearance
  • purple
  • purple
  • white
  • Genotype is the genetic makeup
  • Possible genotype are PP, Pp, pp.

Gene Hypotheses 4
  • The two alleles for a character segregate
    (separate) during meiosis so that each gamete
    carries only one allele for each character, known
    as principle of segregation.

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Punnett Square
  • The alignment of combination of gametes to form
    zygotes with pairs of alleles is random
  • Like tossing a coin.
  • Punnett Square is a diagram that shows all
    possible outcomes of a genetic cross.
  • Used to predict probabilities of outcomes if you
    know the genotypes of the parents

The Testcross
  • Breeds an individual of unknown genotype, but
    dominant phenotype (purple) with a homozygous
    recessive individual (white)
  • Appearance of F1 will reveal the genotype of the
    mystery parent
  • If white flowers are produced, the unknown parent
    must be heterozygous (Pp) and have a recessive

Intermediate Dominance
  • Heterozygotes have a phenotype intermediate
    between the phenotypes of the two homozygote
  • This is referred to as INCOMPLETE DOMINANCE
  • Rules (example snapdragon flowers)
  • Capital/lower case letters not used
  • Instead, a C for color is paired with a
    superscript R for red and W for white
  • CR CR is red and CW CW is white
  • CR CW is pink

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There is a breed of chicken called Andalusians,
black and white parents produce F1 hybrid
offspring, called "blues," with grayish-blue
feathers. Because neither the black nor white
allele is dominant, capital and lowercase letters
are not used to represent them.
Instead, a C for "color" is paired with a
superscript B for "black" or W for "white" to
represent the two alleles. A heterozygote
chicken has one of each allele, CBCW, and is
grayish-blue in color
Although the F1 phenotypes are intermediate, this
inheritance pattern does not support the blending
hypothesis. This is because the parent
phenotypes can reappear in the F2 generation.
Multiple alleles
  • Heterozygote express the distinct traits of both
  • Example Human blood system
  • A, B, AB, or o
  • The letters are antigens found on the surface of
    red blood cells
  • Red blood cells may be coated with one protein
    (A), the other (B), both (AB), or neither (O)
  • There are six possible genotype combinations

ABO blood type is a genetic example of multiple
alleles. There are three alleles in the gene pool
for ABO blood type. IA IB i
IA codes for protein A IB codes for protein
B i codes for neither protein A nor protein B.
Within this multiple allele pool the gene
interactions illustrate both simple dominance as
well as co-dominance.
Remember each individual has only two alleles for
each trait even if there are multiple alleles in
the gene pool. IAIA both
code for A type blood IAi
Phenotype Genotype Protein on RBC (antigen) Antibodies in the blood plasma
Type A IA IA and IA i A b
Type B IB IB and IB i B a
Type AB IA IB A and B -------------
Type O ii ----------- a and b
ABO Blood System
  • Antibodies (proteins) also found in the blood
    serum that attacks foreign antigens
  • Blood A has antibody Anti-B
  • Blood B has antibody Anti-A
  • Blood AB has no antibody
  • Blood O has Antibody Anti A and B
  • Blood O is the universal donor
  • Blood AB can receive any blood type

Rh Factor
  • Rh positive (Rh ) has protein in blood
  • Rh negative (Rh -) has no protein in blood
  • Rh is dominant

Blood Typing
Blood Type Anti-a Sera Anti-b Sera
A Clumping No clumping
B No clumping Clumping
AB Clumping Clumping
O No clumping No clumping
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Sex-linked genes
  • The eggs contain a single X chromosome and sperm
    contain either an X or a Y
  • Sex of the offspring depends on whether the sperm
    that fertilizes the egg has an X or a Y
  • Any gene located on a sex chromosome (X) is
    called a sex-linked gene
  • Most are found on the X (2,000) and few on the Y

Sex-linked traits
  • Written as a XRXr for heterozygous.
  • Y chromosome carries no allele and the phenotype
    is dependant upon the womans allele
  • Therefore, males carry one allele for a
    sex-linked trait.

Sex-linked disorders
  • Red-green blindness
  • Hemophilia (inability of blood to clot)
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