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Monohybrid Crosses,
Co-dominance, and IntermediateWeeks II
Wednesday, September 11 th 2013
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It s time to quizz!!!!!
(b)
(d) (e)
(f)
(a)
(h)
(c)
(g)
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Some important terms in Genetics
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At each locus, a diploid organism possessestwo alleles located on different homologous
chromosomes
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The seventh characteristics of Pisum sativumin Mendels experiments
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Mendels Experiment with Pisum sativum
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Mendelsexperiment
result
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Albinism in human being is usuallyinherited as a recessive trait
(Richard Dranitzke/SS/Photo Researchers)
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The Law of Segregation
Mendel's first law of genetics The two members of a gene pair segregate randomly
and equally into the gametes, which then combine at
random to form the next generation.
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Segregation resultsfrom the separationof homologous
chromosomes inmeiosis
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Phenotypic ratios for simple genetic crosses
(crosses for a single locus)
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Genotypic ratios for simple genetic crosses
(crosses for a single locus)
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Back cross and Test cross
A back cross: mating the F1 hybrid to one of theparental types. There are two possible backcrosses inthe system.
Tt x TT. Back crossing to the dominant parent. The Ttplant will produce 1/2 T gametes and 1/2 t gametes.The TT plant will produce only T gametes. The offspringwill thus be 1/2 TT and 1/2 Tt. Both of these types aretall, so the result of a backcross to the dominant parentis all offspring with the dominant type.
Tt x tt . Back crossing to the recessive parent. The Ttparent produces 1/2 T gametes and 1/2 t gametes, andthe tt parent produces only t gametes. The offspringwill be 1/2 Tt (tall) and 1/2 pp (dwarf). The offspring of atest cross are in the same ratio as the gametes from theorganism being tested: 1/2 T (tall) and 1/2 t (dwarf).
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Test cross :one individual of
unknown genotype iscrossed with another
individual withhomozygous
recessive genotypefor the trait.
How about the backcross?
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Incomplete Dominance
In incomplete dominance the heterozygote exhibits aphenotype that is intermediate between thecorresponding homozygotes and different from either one
Example: Flower color in the four oclock plant Two alleles
C R = wild-type allele for red flower color
C W = allele for white flower color Note how the nomenclature has changed from Cc to
superscripts ("C" is still the gene)
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display
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1:2:1 phenotypicratio NOT the 3:1
ratio observed insimple Mendelianinheritance
In this case, 50% ofthe C R protein is notsufficient to producethe red phenotype
P generation
x
Pink
Gametes
Red White
Gametes
Egg
Sperm
Self-fertilization
C R C W
C W C W C R C R
F1 generation
F2 generation
C R C W
C R
C R
C R
C W
C W
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
C W
C R C R C R C W
C R C W C W C W
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Fruit color ineggplant is inheritedas an incompletely
dominant trait
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In Codominance, heterozygotes express thephenotypes of b o t h parents
The ABO blood group provides an example Phenotype (A, B, AB or O) is determined by the type of
antigen present on the surface of red blood cells Antigens are substances that are recognized by
antibodies produced by the immune system
As shown in figure below, there are three different
alleles that determine which antigen(s) are presenton the surface of red blood cells Allele I A , adds antigen A to H antigen Allele I B , adds antigen B to H antigen
Allele i , doesn't add anything to H antigen
Codominance
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Allele i is recessive to both I A and I B
Alleles I A and I B are codominant They are both expressed in a heterozygous individual
Blood type:
Genotype:
Surface antigen:Serum antibodies:
O
RBC RBC RBC RBC
Antigen A
N-acetyl-galactosamine
Antigen B Antigen B Antigen A
neither A or Bagainst A and B
A I A I A or I A i ii
Aagainst B
B I B I B or I B i
Bagainst A
AB I A I B
A and Bnone
Galactose
(a) ABO blood type
H antigen
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RBC
Glycosyl transferaseencoded by I A allele
N-acetyl-
galactosamine
Activesite
Glycosyl transferaseencoded by I B allele
Galactose
Activesite
RBC
RBC
Antigen A
RBC
Antigen B
(b) Formation of A and B antigen by glycosyl transferase
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Monohybrid Exercises
1. Mendel found that in pea plants, red flower colordominant is over white.a). A heterozygous red flowered plant is crossed with a
white flowered one. Find:a) genotypes of each parentb) genotype and phenotype for F1 generation
b) A homozygous red flowered plant is crossed with awhite flowered one.
a) genotypes of each parentb) genotype and phenotype for F1 generationc) genotype and phenotype for F2 generation
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2. Anto memiliki sifat yang sama dengan kakeknya, yaitu rambut lurus,padahal kedua orang tua Anto berambut keriting. Secara genetikasifat rambut lurus pada kakek Anto adalah (A) dominan (B) resesif (C) intermedier (D) semi dominan
3. Persilangan bunga Mirabilis jalapa merah dengan Mirabilis jalapa putih menghasilkan keturunan F1 berwarna merah muda semua.Bagaimanakah perbandingan fenotip keturunan F2-nya jika terjadipenyerbukan sendiri?(A) 25% merah: 25% merah muda: 50% putih(B) 25% merah: 50% merah muda: 25% putih(C) 75% merah: 25% putih(D) 50% merah: 50% putih.
4. Kakek Wahyu dapat menggulung lidahnya (sifat dominan). KakekWahyu mempunyai dua orang anak yaitu Ayah Wahyu yang dapatmenggulung lidah dan Bibi Wahyu yang tidak dapat menggulunglidah, sama dengan sifat ibu Wahyu. Berapa kemungkinan Wahyudapat menggulung lidahnya?
A.25 % (B) 50 % (C) 75 % (D) 100 %
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5. Sejumlah marmut hitam dari genotip yang sama dikawinkan.Dihasilkan 81 keturunan berwarna hitam dan 28 berwarna
putih. Apa genotip dari kedua induk?6. Bentuk lobak bisa panjang (S LSL), bulat (S RSR) atau oval (S LSR).Jika lobak panjang disilangkan dengan lobak oval, laluketurunan F1 dibiarkan kawin sesamanya secara acak, aparasio fenotipik yang diharapkan pada F2?
7. Jika ayam dengan dibulu berwarna semburat putihdikawinkan dengan ayam berbulu hitam, keturunannya semuabebulu biru batu tulis (biru andalusia). Jika ayam biruandalusia saling disilangkan, dihasilkan keturunan semburatputih, biru, dan hitam berturut-turut dengan rasio 1:2:1.a) Bagaimana cara pewarisan sifat bulu tersebut?
b) Dengan menggunakan simbol-simbol yang sesuai, tuliskangenotip bagi masing-masing fenotip.
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8. A cross of F1-hybrid plants: A genetic cross between two F1-hybridpea plants for spherical seeds will yield what percent spherical-
seeded plants in the F2 generation? (Recall, spherical-shaped seedsare dominant over dented seeds.)(A) 100% (B) 75% (C) 50% (D) 25%
9. A woman with type A blood and a man with type B blood couldpotentially have offspring with which of the following blood types?(A) type A (B) type B (C) type AB (D) type 0(E) all of the above
10. If the unknown is homozygous, all of the offspring of the test crosshave the __________ phenotype. If the unknown is heterozygous, halfof the offspring will have the __________ phenotype.(A) dominant, incompletely dominant (B) recessive, dominant(C) dominant, epistatic (D) codominant, complimentary(E) dominant, recessive
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