Exam 3: Independent Assortment of Genes

Mendel's Y/y;R/r dihybrid pea plants were the F₁ of the cross between a double homozygous dominant and a double homozygous recessive.If we testcrossed these dihybrids,what proportion of the offspring would be recombinant and phenotypically resemble the F₁ dihybrid?

In hogs,a dominant allele B results in a white belt around the body.At a separate locus,the dominant allele S causes fusion of the two parts of the normally cloven hoof resulting in a condition known as syndactyly.A belted syndactylous sow was crossed to an unbelted cloven-hoofed boar,and in the litter there were: $25 \%$ belted syndactylous $25 \%$ belted cloven $25 \%$ unbelted syndactylous $25\%$ unbelted cloven The genotypes of the parents can best be represented as which of the following?

An arginine-requiring strain of Neurospora is crossed to a wild-type (prototrophic)strain. a)In the first cross,half of the progeny are arginine-requiring and half are wild type.What does this tell you about the genetic basis of the arginine-requiring mutant? b)In the second,the progeny are 83 arginine-requiring and 13 wild type.The germination percentage of ascospores is 95/100%.Explain these results simply,and tell briefly how you would confirm your explanation.

Fruit color in a particular plant is controlled by a set of three QTLs (quantitative trait loci,or "polygenes")that work in an equal and additive manner.Each QTL has two alleles (i.e. ,A and a);each allele represented by a capital letter produces one dose of yellow pigment,while alleles represented with lower case letters do not produce any pigment at all. -Assuming no effects by the environment,how many different shades of yellow fruit color are there?

Meiosis I is about to start in a cell of a plant in which 2n = 18.At this stage,the cell has:

Two pure lines obtained from Mendel's experiments are crossed to each other.The first line makes green smooth seeds (peas),and the second line has white flowers.All F₁ individuals have purple flowers and produce yellow wrinkled seeds.What proportion of the F₂ plants should have purple flowers and make green wrinkled seeds?

Two pure-breeding mutant plants were crossed: One had small leaves (wild-type leaves are large),and the other made pink flowers (wild-type flowers are purple).All F₁ individuals had small leaves and purple flowers.Assuming independent assortment,what proportion of the F₂ individuals are expected to be phenotypically wild type?

Which of the following is/are TRUE with respect to haploid and diploid cells?

In a species of Mexican mollies,fish with ragged fins and nonragged fins were found.When mollies of a true-breeding (i.e.,pure-breeding)ragged strain were crossed with nonragged fish,the F₁ all had ragged fins,and in the F₂,three ragged appeared to one nonragged.Diagram this cross,letting R = ragged and r = nonragged,and give parental phenotypes,genotypes,and germ cells,as well as F₂ genotypes and phenotypes.

A leucine-requiring mutant strain of haploid yeast is crossed to a cysteine-requiring mutant strain.Assuming independent assortment,what proportion of the spores produced will be mutant?

In a diploid organism 2n = 6,and there are two long,two intermediate,and two short chromosomes.What is the most accurate representation of a gamete resulting from meiosis in this organism?

The following is known about the inheritance of size and fur color in Holland lop rabbits: •Crosses between large individuals only produce large individuals. •Crosses between dwarf individuals produce both large and dwarf rabbits in a ratio of 1:2.Such crosses also produce some very small kits (baby rabbits)that generally die within a few days. •Crosses between brown rabbits only produce brown kits. •Some crosses between black rabbits produce only black kits,whereas others produce both black and brown kits. •The size and fur-color phenotypes segregate independently. -A large black doe (female rabbit)gives birth to nine black kits?five are large,and four are dwarf.What are the possible phenotypes of the kits' father?

A fish of genotype a/a;B/b is crossed to a fish whose genotype is A/a;B/b.What proportion of the progeny will be heterozygous for at least one of the genes? (Assume independent assortment.)

The following is known about the inheritance of size and fur color in Holland lop rabbits: •Crosses between large individuals only produce large individuals. •Crosses between dwarf individuals produce both large and dwarf rabbits in a ratio of 1:2.Such crosses also produce some very small kits (baby rabbits)that generally die within a few days. •Crosses between brown rabbits only produce brown kits. •Some crosses between black rabbits produce only black kits,whereas others produce both black and brown kits. •The size and fur-color phenotypes segregate independently. -What are the expected phenotypes in the F₁ of a cross between a dwarf rabbit that breeds true for brown fur color and a large rabbit that breeds true for black fur color?

Several pairs of light brown hamsters with identical genotypes were mated.Altogether,the F₁ was comprised of 143 individuals: 62 light brown,41 brown,38 beige (very,very light brown),1 dark brown,and 1 white.What mode of inheritance of the phenotype "fur color" could most easily explain these results?

Which diagram most accurately shows the arrangement of homologous chromosomes during the first metaphase of meiosis?

Define Mendel's experimental evidence for diploid chromosome content in pea plants.

If two mice of genotype F/f;G/g;H/h;I/i;J/j are repeatedly mated,how many different phenotypes will be found in the progeny? (Assume complete dominance for all genes.)

Two albino strains of Neurospora crassa were isolated in two different laboratories.When either one was mated with wild type (orange)it produced 1/2 albino: 1/2 orange progeny. a)What can you now deduce about the genetics of each of these albino strains? b)Assume first that the two strains carry allelic mutations.Using appropriate symbols,diagram a cross of the two albino strains.Include the genotypes of the parents,a stick-and-circle diagram of the relevant chromosomes at metaphase I of meiosis,and the genotypes and ratios of the progeny. c)Now assume that the two strains carry mutations in different genes,and that the genes are on different chromosomes.Answer the same questions as above.Assume that there are no crossovers between either gene and the centromeres.

A corn plant of genotype A/a;B/B;C/c;D/d;E/e;f/f;G/g is selfed.What is the probability of producing a completely homozygous individual out of all possible offspring?