Download Mendelian Genetics

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 Heterozygous
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 Nucleic Acid
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 Deoxyribose
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 Punnett square •
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 Karyotype
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 Allele
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 Zygote
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 Purebred
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 Hybrid
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 Fertilization
 Homozygous
Trait
• Generation
Heredity
• Monohybrid cross
Genetics
• Dihybrid cross
Inheritance
• Segregation
Genome
• Nucleotide
Gene
• Pedigree
Chromosome
• Diploid
Genotype
• Dominant
Phenotype
• Recessive
Haploid
Gamete
Meiosis
Variation/variability
Terms to Know and Use
• Genome- The complete set of all chromosomes
• Genetics- The study of heredity
• Gene – A piece of DNA that controls the
synthesis of a specific protein
• Trait – expression of a gene: i.e. a purple flower,
determined by DNA
• Dominant trait - expressed over recessive trait
when both are present
• Recessive trait - not expressed when the
dominant trait is present
• Allele - a variation of a gene responsible for
different versions of the same trait. Use
letters to represent alleles (A or a, T or t)
• Chromosome – condensed strand of DNA
containing several genes
• Locus - location of a gene/allele, on a
chromosome
• Haploid - one copy of a chromosome
• Diploid - two copies of a chromosome
• Gamete – haploid sex cell (sperm or egg)
• Zygote - cell resulting from the fusion of
two gametes, they are diploid
• Genotype - the type of alleles on a
chromosome: genetic makeup
• Phenotype - The way a genotype is
expressed: i.e. the color of a flower
• Purebred - organisms that always pass the
same genotype to their offspring
• Hybrid - offspring resulting from
crossbreeding two true breeding lines: F1
• Homozygous- genotype with two of the
same type of allele ex: BB or bb, aka
purebred
• Heterozygous- genotype with two different
alleles. Ex: Bb, aka hybrid
I praise the tender flower, That on a mournful day
Bloomed in my garden bower And made the winter gay.
Its loveliness contented My heart tormented. I praise the
gentle maid Whose happy voice and smile To confidence
betrayed My doleful heart awhile; And gave my spirit
deploring Fresh wings for soaring. The maid for very fear
Of love I durst not tell: The rose could never hear,
Though I bespake her well: So in my song I bind them
For all to find them.
 1822- 1884
 Austrian monk
 Experimented with pea
plants
 He thought that ‘heritable
factors’ (genes) retained
their individuality
generation after
generation
 1831 Charles Darwin joins crew of Beagle
 1839 Schleiden and Schwann propose the Cell Theory
 1847 Semmelweiss proposes that infection is spread by
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


contaminated hands of physicians.
1856 Mendel begins hybridization studies with garden peas
1857 Louis Pasteur (France) introduces the Germ Theory of
Disease.
1859 Darwin publishes Origin of Species
1865 Mendel presents presents his results in transmission of
phenotypic traits between the generations to the Brünn Society of
Natural Sciences.
1900 Hugo de Vries in Holland, William Bateson in Great Britain,
Franz Correns in Germany, and Erich Tschermak in Austria
acknowledged Mendel's legacy, and hailed him as the true father of
classical genetics.
 Mendel disagreed with
the “Blending Theory”
of inheritance.
 Started with 34 kinds
peas Pisium sativum
 After 2 years he had 22
purebreds
http://www.dnaftb.org/dnaftb/1/concept/index.html
Tall
Straight
 There are alternate forms
of ‘genes’=alleles
 For each trait, organisms
have 2 alleles, one from
mom & one from dad
 Pollen and egg each carry
1 allele/trait because alleles
segregate
 When only one allele is
expressed & other has no
noticeable effect, it is
dominant

http://www.sumanasinc.com/webcontent/anisam
ples/nonmajorsbiology/independentassortment.ht
ml
1. Plants must possess constant
differentiating characteristics.
2. The hybrids of such plants
must, during the flowering
period, be protected from the
influence of all foreign pollen,
or be easily capable of such
protection.
3. The hybrids and their offspring
should suffer no marked
disturbance in their fertility in
the successive generations.
Mendel's Laws of Inheritance
1st Law
• Law of Segregation during gamete
formation allele pairs separate or segregate,
into different gametes
• 1) The Law of Segregation: Each inherited trait is defined by a gene
pair. Parental genes are randomly separated to the sex cells so that sex
cells contain only one gene of the pair. Offspring therefore inherit one
genetic allele from each parent when sex cells unite in fertilization
• (Demonstrated with a “test cross” aka
Punnett square).
Smooth Tall
Smooth
Tall
Smooth wrinkled
short
Tall
wrinkled
short
Two chromosomes of one parent are represented on the left.
Possible alleles passed on to the offspring are on the right.
(Consider smooth or wrinkled peas AND tall or short plants)
Mother contributes:
True Breeding
A
or
A
A
AA
AA
A
AA
AA
Mother contributes:
Cross Breeding
a
or
a
A
Aa
Aa
A
Aa
Aa
 Law of Independent Assortment suggested that each allele
pair segregates independently of other gene pairs during gamete
formation
 2) The Law of Independent Assortment: Genes for different traits
are sorted separately from one another so that the inheritance of
one trait is not dependent on the inheritance of another
 (Demonstrated with a dihybrid cross).
 http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/i
ndependentassortment.html
So how can you show a cross with 2
traits?
For example: Round and Yellow crosses
with a Round and Yellow
RrYy x RrYy
Dihybrid Cross
SsBb x SsBb
Mother contributes:
SB Sb
SB
SSBB
sB
sb
SSBb
SsBB
SsBb
Sb
SSbB
SSbb
SsbB
Ssbb
sB
sSBB
sSBb
ssBB
ssBb
sb
sSbB
sSbb
ssbB
ssbb
 Law of Dominance: The dominant gene will be
expressed over the recessive gene
 3) The Law of Dominance: An organism with alternate
forms of a gene will express the form that is dominant.