genetics 2nd weeks, monohybrid crosses

8/10/2019 Genetics 2nd Weeks, Monohybrid Crosses

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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

genetics 2nd weeks, monohybrid crosses

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