genetika zadaci

8/13/2019 genetika zadaci

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Concept of the gene idea,the concepts of genetics


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Briefly genetic is the science

which investigates heredity anddiversity.

Genetic is derived from term genesiswhich means creation.

Today is the branch of biology which studyhow traits are passed from one generation

to next.


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Genetic concepts

Heredity : passing on traits from parentsto their offspring.Trait :charcteristic of an organism

Gene : a segment of DNAAllele :one pair of genes, one commingfrom mother, other from the father. Allelesis a specific version of genes.


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Locus is a specific location of a gene.Heterozygote means you have differentalleles for a given trait (Aa, Bb, Cc).Homozygote means you have same alleles(AA, BB, cc, dd).

Dominant gene is gene that is alwaysexpressed. Recessive is expressed whenpaired is aa.


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Phenotype is physical visible characteristic oforganism.

Genotype is complete set of genes of a livingthings.Independent genes are alleles for differenttraits located on different location.

Linked gene is when there is more than onegene on a single chromosome. They can beseparated from each other by crossing overin meiosis.


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Parenteral cross (P) is mating the fatherand mother.

Filia (F): the individuals produced bycrossing the father and mother.


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What is phenotype?

Round R is dominant to wrinkled r.

Yellow Y is dominant to green y.

Classify the following as homozygotes orheterozygotes? RR, Rr, Yy, YyRr.


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The law of probability and itsapplications

Probability is the branch of matematicsthat predict chances that a certain eventwill occure.

It is the study of operations of the laws of

chance.


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Law of segregation is also knownas Mendel s first law.


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Laws of probability can be used to predictoutcomes of genetic crosses.

Probability is calculated as the number ofexpected outcomes / number of possible

outcomes.


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What is the probability that a coinwill land a heads up?

Number of expected outcomes_______Number of possible outcomes _______

P= #of expected outcomes/#of possibleoutcomes


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What is the probability that youwill roll an even number on a die?

Number of expected outcomes_______Number of possible outcomes _______

P= #of expected outcomes/#of possibleoutcomes


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Genetic cross can not be made withoutknowing the gamete type.

Alleles are different form of genes.Homozygous alleles AA, aa.

Heterozygous Aa.


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When you do crosses you should knowhow many gametes each person shouldhave.

Rr x Yy

rr x yyAaBbCC


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What is the probability of havingalbino child if the parents are bothheterozygous for condition?

Albinism is lack of pigment melanin. It isdue to absence enzyme tyrosinase.Albinism is autosomal recesive condition.


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Huntington s disease is autosomaldominant. What is the probability of ahaving child with the disease if oneparents is homozygous recesive, other isheterozygous?


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What Mendel did?


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Produce five different generations in shorttimesHave many different types that couldgrow in the gardenHave genes that are independed

Have reproductive organs closed to thepetalsHave 7 contrasting traits


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Mendel's observations from theseexperiments can be summarized in twoprinciples:1. the principle of segregation2. the principle of independentassortment


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The principle of independentassortment

Different pairs of alleles are passed tooffspring independently of each other.The result is that new combinations ofgenes present in neither parent arepossible.


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Gene is a factor of heritance.Alternative forms are called alleles.Genotype is combination of alleles.Pairs of genes are located onchromosomes and each embryo gets one

copy chromosome from the mom otherfather.


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What happens to homologouschromosome in meiosis?Gene pairs are separated because theyare located on homologous chromosome(segregation-separation).Phenotypes are traits.


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In summer squash, white fruit color (W) isdominant over yellow fruit color (w) and disk-

shaped fruit (D) is dominant over sphere-shaped fruit (d).. If a squash plant true-breeding for white, disk-shaped fruit iscrossed with a plant true-breeding for yellow,sphere-shaped fruit, what will thephenotypic and genotypic ratios be for:

a. the F1 generation? b. the F2generation?


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1. Write down the cross in terms of theparental (P1) genotypes and phenotypes2. Determine the P1 gametes, place themin a Punnett Square and fill in theresulting genotypes:3. Determine the genotypic and phenotpicratios for the F1 generation4. Write down the cross between F1progeny


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Genotypic ratios:1/16 will be homozygous dominant for both traits (WWDD)2/16 will be homozygous dominant for color and heterozygous for shape(WWDd)2/16 will be heterozygous for color and homozygous dominant for shape(WwDD)1/16 will be homozygous dominant for color and homozygous recessive forshape (WWdd)4/16 will be heterozygous for both traits (WwDd)2/16 will be heteozygous for color and homozygous recessive for shape(Wwdd)1/16 will be homozygous recessive for color and homozygous dominant forshape (wwDD)2/16 will be homozygous recessive for color and heterozygous for shape(wwDd)1/16 will be homozygous recessive for both traits (wwdd)

This is a 1:2:2:1:4:2:1:2:1 genotypic ratio!


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Phenotypic ratios:9/16 will have white, disk-shaped fruit3/16 will have white, sphere-shaped fruit3/16 will have yellow, disk-shaped fruit1/16 will have yellow, sphere-shaped fruit

This is a 9:3:3:1 phenotypic ratio.


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1. In rabbits, white fur color (W) isdominant to black, and long ears (L) aredominant to short. Draw a Punnettsquare that represents the cross betweentwo rabbits heterozygous for both traits.What are the phenotype and genotyperatios?


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2. In humans, polydactylism (having anextra finger on each hand) is dominant to thetypical 5-finger arrangement. Tongue rollingis dominant to not being able to roll one stongue. A man who is homozygous for 5-fingers and who cannot roll their tongue haschildren with a woman who is heterozygousfor polydactylism and tongue rolling. Draw aPunnett square that represents the cross.What is the probability the couple willproduce a polydactyl baby who cannot rolltheir tongue?


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3. A species of bird is threatened with extinctionbecause its habitat is being destroyed bydeforestation. As a research ecologist, you havebeen chosen to ensure the genetic diversity ofthe species. In this species of bird, feathers maybe white, black, or white with black spots. In thesame species, beaks may be long, medium orshort. A black bird with a medium beak pairswith a spotted bird with a long beak. Draw aPunnett square that represents the cross. Makea list of all of the phenotype combinations thispair could possibly produce.


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4. A man with a dimple and brown eyes(whose father had blue eyes but nodimples) marries a woman with a dimpleand brown eyes (whose father had blueeyes with no dimple). What is the

probability their first child will be blue eyedand without dimple? (assume that dimple isdominant over smooth cheeks and browneyes are dominant over blue).


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Mendel findings:

Traits are inherited trough genes

The traits of pea plant are related to itsalleles which can be samo or different

If the pairs of alleles forming a gene aredifferent, the efects of dominant alleleappears in the phenotype


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Variety in organism arises from the factthat, during fertilization the gametes

combine randomly, allowing the genes forvarious traits to form new combinations

Traits are visible on offspring inpredictable ratios, according the principleof probability.


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Forked lined method!


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Male have phenotype AaBBCc cross withfemale genotype aaBbCc.

What are expecting genotype frequencytheir offspring?


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Using the forked lined approach in atrihybrid cross involving three traits ,

where the pigments are both AaBbCc,what is the probability of their producingan offspring recesive for all three traits?

What is the probability of producing anoffspring with genotype AabbCc?


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a. Give the phenotypes of the flies in your test-cross:___________X___________

b. If all of the offspring turn out to be red-eyed (all347 of them!!!) what would the genotypes of the fliesused in your test- cross? (Use R and r)

___________X__________ Diagram the cross:

Genotypic ratio= ______________ Phenotypic ratio=______________


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c. If about 179 of the 347 show up withsepia eyes, what was the actual genotype

of your new found friend? _______________


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Step 1: Figure out the genotypes of theparents.Step 2: Figure out what kinds of gametesthe parents can produce.Step 3: Set up a Punnett Square for yourmating.Step 4: Fill in the offspring inside the tableby matching the egg allele at the top of thecolumn with the sperm allele at the head ofthe row.Step 5: Figure out the genotypic ratio foryour predicted offspring.

Step 6: Figure out the phenotypic ratio foryour predicted offspring.Step 7: Answer the question you've beenasked.


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The trick is to recognize when you aredealing with a question involving

incomplete dominance. There are twosteps to this:1) Notice that the offspring is showing a3rd phenotype. The parents each have

one, and the offspring are different fromthe parents.2) Notice that the trait in the offspring is ablend (mixing) of the parental traits.


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1. A cross between a blue bird & a whitebird produces offspring that are silver.

The color of birds is determined by justtwo alleles.a) What are the genotypes of the parentbirds in the original cross?

b) What is/are the genotype(s) of thesilver offspring?c) What would be the phenotypic ratios ofoffspring produced by two silver birds?


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The color of fruit for plant "X" isdetermined by two alleles. When two

plants with orange fruits are crossed thefollowing phenotypic ratios are present inthe offspring: 25% red fruit, 50% orangefruit, 25% yellow fruit. What are thegenotypes of the parent orange-fruitedplants?


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CODOMINANCE

First let me point out that the meaning of theprefix "co-" is "together".Cooperate = work together. Coexist = existtogether. Cohabitat = habitat together.

With codominance, a cross betweenorganisms with two different phenotypesproduces offspring with a third phenotype inwhich both of the parental traits appeartogether.


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A very common phenotype used inquestions about codominance is roan fur

in cattle. Cattle can be red (RR = all redhairs), white (WW = all white hairs), orroan (RW = red & white hairs together).A good example of codominance.

Another example of codominance ishuman blood type AB, in which two typesof protein ("A" & "B") appear together onthe surface of blood cells.


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Codominance is when twodominan alleles are beingexpressed in the same time.


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1. Predict the phenotypic ratios ofoffspring when a homozygous white cow

is crossed with a roan bull.2. What should the genotypes &phenotypes for parent cattle be if afarmer wanted only cattle with red fur?


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In a certain fish, blue scales and redscales are codominant. When a fish has

the genotype B R, it has a patchwork ofblue and red scales. What happens if youbreed this fish with a fish that only hasBlue Scales.


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Step 1: Determine the genotypes of theparents

B R = patchwork fish

B B = blue fish

R R = red fish


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Step 2: Set up the Square


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Step 3: Count the number of eachphenotype:

1/2 will by patchwork, 1/2 will be blue

What happens when you cross two patchworkfish?


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Flower like a petunia, the allele for redflower is incompletely dominant over the

allele for white flower colour. When a redflower is crossed with a white one, anintermediate pink flower results. Showthe genotypes of the parents and the F1generation of a cross between a red anda white four o'clock flower.


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In guinea pigs, colour of coat isdetermined by at least three alleles.

Yellow coat is determined by thehomozygous genotype YY, white by thehomozygous genotype WW, and cream bythe heterozygous genotype YW.


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Multiple alleles

Multiple alleles means that there arethree or more forms of a gene for a trait.


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Epistasis

Epistasis is a phenomenon in which theexpression of one gene depends on the

presence of one or more 'modifier genes .


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Pleiotropy

Pleiotropy is defined as the phenomenonin which a single locus affects two or more

distinct phenotypic traits.


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Polygenic inheritance

Polygenic inheritance is when a single traitis controlled by 2 or more sets of alleles.

Most human traits are polygenicallyinherited. Examples would be skin andeye color. This explains how you can haveseveral different phenotypes for one traitand how parents can have offspring witheye color or skin color different from whatthey have.


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By considering a chromosome a linearsequence of genes, Sturtevant assigned

each gene he was studying in fruit flycrosses a position on the chromosomeusing recombination frequencies.


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This type of genetic map is called a linkagemap because it portrays the sequence of

genes along a chromosome, but it does notgive the precise location of the genes.Sturtevant expressed the distance betweengenes in map units. By definition, one map

unit (1 m.u.) is equivalent to a 1%recombination frequency. In honor ofMorgan, one map unit, or a 1% frequency, isalso called one centimorgan (cM).


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Coat colors of dogs depend upon the action of at leasttwo genes. At one locus a dominant epistatic inhibitorof coat color pigment (I-) prevents the expression ofcolor alleles at another independently assorting locus,producing white coat color. When the recessivecondition exists at the inhibitor locus (ii), the allelesof the hypostatic locus may be expressed, iiB-producing black and iibb producing brown. Whendihybrid white dogs are mated together, determine(a) the phenotypic proportions expected in theprogeny, (b) the chance of choosing, from among thewhite progeny, a genotype that is homozygous atboth loci.


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6 M ki d f ild i l h h i


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6. Many kinds of wild animals have the agouticoloring pattern in which each hair has a yellow bandaround it. /10p

a. In black mice and other black animals, the yellowband is not present and the hair is all black. Thisabsence of wild agouti pattern is called nonagouti.When mice of a true-breeding agouti line are crossedwith nonagoutis, the F1 is all agouti and the F2 has a

3:1 ratio of agoutis to nonagoutis. Diagram thiscross, letting A - agouti and a = nonagouti. Show thephenotypes and genotypes of the parents, theirgametes, the F1, their gametes and the F2.


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Sickle cell anemia (SCA) is a human geneticdisorder caused by recessive allele. A coupleplans to marry and wants to know theprobability that they will have affected child.With your knowledge of Mendelianinheritance, what can you tell them if (a)both are normal, but each has one affected

parent and the other parent has no familyhistory of SCA; and (b) the man is affectedby disorder, but the woman has no familyhistory of SCA?


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Matings between black rats of identicalgenotype produced offspring as follows:

14 cream-colored, 47 black, and 19albino. (a)What epistatic ratio isapproximated by these offspring? (b)Whatare the genotypes of the parents and theoffspring (use your own symbols)?


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If we use the same example we followedabove, but substitute the albino gene for

the earlobe gene, we can see the effectthat epistasis has on the phenotypic ratio.The entire problem is worked exactly thesame way, until the final determination ofphenotypic ratio.


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When it comes to that phenotypequestion, we have to recognize that any

child with the aa genotype will be albino,and will have red eyes, no matter whatthe eye color alleles are. So our final ratiowill be 9 Brown Eyed : 3 Blue Eyed : 4Red Eyed (albino).

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