Biology 1201A Chapter Notes - Chapter 10-11: Pleiotropy, Abo Blood Group System, Epistasis

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18 Oct 2016

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Blending theory of inheritance- suggested that hereditary traits blend evenly in offspring through mixing of the parent"s blood. Homozygous- state of possessing two copies of the same allele (pp) (pp) Homozygote- an individual with two copies of the same allele. Heterozygous- state of possessing two different alleles of a gene (pp) Heterozygote- an individual with two different alleles of a gene. Monohybrid- an f1, heterozygote produced from a genetic cross that involves a single character (pp x. Testcross- a genetic cross between an individual with the dominant phenotype and a homozygous recessive individual. Dominant- refers to the allele expressed when more than one allele is present. F1 generation- the first generation of offspring from a genetic cross. Chose garden peas for his research b/c the plant could be grown easily without elaborate equipment. K(cid:374)o(cid:449)(cid:374) to (cid:271)e (cid:862)true (cid:271)reedi(cid:374)g(cid:863); that is, (cid:449)he(cid:374) self-fertilized, they passed traits without change from one generation to the next.

Related Questions

Problem A. You cross two homozygous parents: RRYY (round yellow) and rryy (wrinkled green) to produce an F1 generation. Round seeds are dominant, yellow seeds are dominant. You cross two F1s to produce the F2 generation. In the F2 generation, you find an individual with round yellow seeds. You do a testcross to find out the genotype of this âmysteryâ dominant/dominant phenotype. In the offspring of the cross, you find 1?2 have round yellow seeds and 1?2 have wrinkled yellow seeds.

1. Based on these data what was the genotype of the mystery F2?

Problem B. You carry out a dihybrid cross between a red-flowered rose with long pollen grains (A1A1 LL) and a white-flowered rose with round pollen (A2A2 l l). The flower color gene (A) shows incomplete dominance, and long pollen is completely dominant to round pollen. The genes for these traits are on different chromosomes so assort independently

2. What would be the phenotypes of the F1 generation?

3. What fraction of the F2 generation is expected to have red flowers and long pollen? (As always when traits are independent, what rule can you apply to save time?)

Problem D. In the example of epistasis presented in class, the agouti allele in mice (A) codes for striped hairs and is dominant to the allele for all black hairs (a). A loss-of-function allele for the pigment gene (b) produces no pigment and is recessive to the normal, dominant allele (B). The recessive allele at b masks the effect of the A gene. A dihybrid cross of AABB and aabb is carried out.

5. Name all of the genotypes in the F2 generation that can produce an albino (no pigment) phenotype.

Problem E. A cross is made between homozygous fruit flies that differ for eye color (the st gene) and

body color (the e gene). The F1 double heterozygote is shown below using chromosome notation.

st+ e

--------------------------------------

st e+

st = the recessive allele for scarlet eyes; st+ = the dominant wildtype allele for red eyes e = the recessive allele for ebony body; e+ is the dominant wildtype allele for gray body

6. Are the chromosomes shown in the genotype above in cis or trans configuration?

7. Based on this notation, what were the genotypes and phenotypes of the two parents of the F1? (Think carefully here...)

8. With what phenotype would you cross this F1 to measure recombination frequency?

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These all relate to exceptions to the inheritance patterns encountered by Mendel.â

Why do multiple and lethal alleles often result in modifications of the classic Mendelian monohybrid and dihybrid ratios?

Select the four correct statements.

-When an essential gene is mutated, it can result in a lethal phenotype. There are no classic Mendelian monohybrid and dihybrid ratios.

-In the case of codominance, heterozygotes produce gene products from both alleles of a gene. Classic Mendelian monohybrid and dihybrid ratios are modified by codominance.

-In the case of incomplete dominance, the phenotype of the heterozygote is distinct from and often intermediate to the phenotypes of homozygous individuals. Classic Mendelian monohybrid and dihybrid ratios are modified by incomplete dominance.

-Genes exist in a large number of allelic versions and a diploid organism has two homologous gene loci that may be occupied by different alleles of the same gene. This can result in many different phenotypes for traits, which may not follow typical Mendelian ratios.

-When an essential gene is mutated, it can result in a lethal phenotype. This results in a modification of classic Mendelian ratios.

-The phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. The joint expression of both alleles in a heterozygote is called codominance. There are no classic Mendelian monohybrid and dihybrid ratios.

-Genes exist in a large number of allelic versions, but in a diploid organism, only one allele of the gene can occupy one homologous gene loci. Classic Mendelian inheritance cannot explain this phenomenon.

-Each gene produces a unique gene product. The effect of one allele in a heterozygote completely masks the effect of the other. Classic Mendelian genetics cannot explain this phenomenon.

1. Imagine hypothetically that the gender of a reptile iscontrolled by a single gene with two alleles, designated Aand a. The outcome of this trait is affected by thetemperature of the environment. When raised in a coolerenvironment, the dominant A allele confers maleness, andthe a allele confers femaleness. However, when raised in awarmer environment, the homozygote aa animal is male. If aheterozygous individual is crossed to a female reptile, what arethe proportions of offspring that are male and female when raisedin a cool environment? How do the proportions change if theoffspring are raised in a warm environment?

2. In the laboratory, a genetics student crossed flies withnormal long wings to flies with mutant short wings, which thestudent believed to be a recessive trait. In the F1 generation, allflies had long wings. In the F2 generation, the following resultswere obtained:

792 long-winged flies and 208 short-winged flies

Is this gene behaving according to standard Mendelian genetics?What do the data suggest about the short-winged mutation?

Biology 1201A Chapter Notes - Chapter 10-11: Pleiotropy, Abo Blood Group System, Epistasis

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