Exam 4: Extensions of Mendelian Genetics

The term expressivity defines the percentage of individuals who show at least some degree of expression of a mutant genotype.

State a significant difference between X-linked and sex-influenced inheritance.

Genomic anticipation refers to observations that a genetic disorder occurs at an earlier age in successive generations,whereas genetic imprinting occurs when gene expression varies depending on parental origin.

Assume that a cross is made between two organisms that are both heterozygous for a gene that shows incomplete dominance.What phenotypic and genotypic ratios are expected in the offspring?

Many of the color varieties of summer squash are determined by several interacting loci: AA or Aa gives white,aaBB or aaBb gives yellow,and aabb produces green.Crosses among heterozygotes give a 12:3:1 ratio.What type of gene interaction would account for these results?

A mutation in a gene often results in a reduction of the product of that gene.The term for this type of mutation is ________.

A 9:7 ratio indicates incomplete dominance.

The trait for medium-sized leaves in iris is determined by the genetic condition PP'.Plants with large leaves are PP,whereas plants with small leaves are P'P'.The trait for red flowers is controlled by the genes RR,pink by RR',and white by R'R'.A cross is made between two plants each with medium-sized leaves and pink flowers.If they produce 320 seedlings,what would be the expected phenotypes,and in what numbers would they be expected? Assume no linkage.

What is meant by the term epistasis? Distinguish between epistasis and dominance.Do not use examples in answering this question.

A mutant gene that produces brown eyes (bw)is located on chromosome #2 of Drosophila melanogaster,whereas a mutant gene producing bright red eyes,scarlet (st),is located on chromosome #3.Phenotypically,wild-type flies (with dull red eyes),whose mothers had brown eyes and whose fathers had scarlet eyes,were mated.The 800 offspring possessed the following phenotypes: wild type (dull red),white,scarlet (bright red),and brown.Most of the 800 offspring had wild-type eyes,whereas those with white eyes were the least frequent. a) Using standard symbolism,diagram the cross from the P generatio $\text { (brown-eyed mothers } \times \text { scarlet-eyed fathers) }$ n and the F₁ generation.Be certain to provide the alleles of the mutant genes. b) From the information presented above,how many white-eyed flies would you expect in the F₂ generation?

Multiple mutations that are found to be present in a single gene are said to belong to the same ________ group.

With incomplete dominance,a likely ratio resulting from a monohybrid cross would be ________.

With multiple alleles,there can be more than two genetic alternatives for a given locus.

Pattern baldness and hen/cock feathering in fowl are examples of X-linked inheritance.

The accompanying figure is a pedigree of a fairly common human hereditary trait in which the boxes represent males and the circles represent females.Shading symbolizes the abnormal phenotype. Given that one gene pair is involved: a) Is the inheritance pattern X-linked or autosomal,recessive or dominant? b) Give the genotype of each individual in the pedigree.If more than one genotypic possibility exists,present all possible alternatives.

Assume that a dihybrid cross is made in which the genes' loci are autosomal,independently assorting,and incompletely dominant.How many different phenotypes are expected in the offspring?

Two forms of hemophilia are determined by genes on the X chromosome in humans.Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man.What is the probability that their first son will have hemophilia?

A cross was made between homozygous wild-type female Drosophila and yellow-bodied male Drosophila.All of the resulting offspring were phenotypically wild type.Offspring of the F₂ generation had the following phenotypes: Sex Phenotype Number male wild 96 male yellow 99 female wild 197 Based on this information: a) Is the mutant gene for yellow body behaving as a recessive or dominant? b) Is the yellow locus on an autosome or on the X chromosome?

"Gain of function" mutations are generally dominant since one copy in a diploid organism is sufficient to alter the normal phenotype.

In mice,there is a set of multiple alleles of a gene for coat color.Four of those alleles are as follows: C = full color (wild) cᶜʰ = chinchilla cᵈ = dilution c = albino Given that the gene locus is not sex-linked and that each allele is dominant to those lower in the list,diagram the crosses indicated below and give the phenotypic ratios expected from each. a) wild (heterozygous for dilution)× chinchilla (heterozygous for albino) b) chinchilla (heterozygous for albino)× albino