BIOL239 Study Guide - Final Guide: Trisomy, Fragile X Syndrome, Centromere

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browncockroach329

16 Oct 2011

School

University of Waterloo

Department

Biology

Course

BIOL239

Professor

Christine Dupont

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Document Summary

Phenotype - observable characteristic (largely determined by genotype). Monohybrid cross matings between individuals that only differ in one trait. Allele alternative form of a single gene. Polymorphic more then one wildtype allele; allele frequency greater than 1% Monomorphic only one wildtype allele; only one allele above 1% frequency. The two alleles for each trait separate (segregate) during gamete formation then unite at random, one from each parent, at fertilization. At the dna level, alleles vary in nucleotide sequence. This can result in: new amino acid sequence, change in the amount of protein, e. g. Garden peas r gives the pea a round shape because this version of the starch. The r allele as a different amino acid sequence and the enzyme is non-functional (i. e. no branched starch). Test cross breeding an unknown genotype with the homozygous recessive will reveal its genotype. If it was homozygous dominant, all progeny are heterozygous and have the same phenotype.

Related Questions

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.

In Drosophila melanogaster, the allele n gives notched wings while the wildtype allele n⁺ gives normal wings. At a separate gene, the allele sb gives stubby legs while wildtype sb⁺ allele gives normal legs. At a third gene, the allele w gives white eyes while wildtype w⁺ allele gives red eyes. A female individual heterozygous for these three genes is testcrossed and 2090 progeny are produced. They are classified as follows: 17 wildtype

15 notched, stubby, white

126 stubby, white

122 notched

817 white

813 notched, stubby

87 stubby

93 notched, white

(Unless otherwise stated, assume a trait not mentioned explicitly in the classification is the wildtype phenotype e.g. 122 notched = 122 notched wings, normal legs, red eyes.)

1. Write out the genotype of the triply heterozygous mother (i.e. draw the alleles in their proper order on the two chromosomes of the triple heterozygote). Explain your reasoning with respect to the frequencies of the different classes of progeny produced.

(4 marks)

2. Draw a genetic map of the three genes on the chromosome indicating map distances (in m.u.) between genes. Show your calculations.

(3 marks)

3. Calculate the interference. Show your calculations.

lavendergrasshopper447

1. Ifa species of flower has the allele R (red) which is incompletelydominant to the allele r (white) what color is the genotype of anindividual with a red flower? Choose as many as areappropriate. (Points: 2) RR
Rr
rr
R
r

2. A gene can be defined as... (Points :2)

alternateforms of the DNA for a trait
geneticcombination that determines the observable form of a trait
partof the DNA that codes for a specific protein
theobservable form of a trait

3. A homozygote is an individual in which(Points : 2)

allelesof the gene pair are different
allelesof the gene pair are identical
genesare homolgous
traitsare passed from parents to progeny

4. Which of the following might be aphenotype? (Points : 2)

A
Aa
pinkflowers
AaDd

5. What does "F2 generation" refer to? (Points: 2)

theparents
theoffspring of the parental generation
theoffspring of crossing the F1 generation with itself
theoffspring of crossing the F1 generation with the parentalgeneration

6. Which of the following genotypes isheterozygous? (Points : 2)

Aa
AABB
A
a

7. Which statement best describes a dominantallele? (Points : 2)

theallele expressed in the homozygote
theallele expressed in the heterozygote
theallele that is most common in the population
theallele that is lethal