Molgen Module 1

You are viewing a pedigree and trying to determine the inheritance pattern of a trait. List three characteristics that, if observed, would indicate that the trait is autosomal recessive.

-equal amount of males and females have the trait -can show up if neither of the parents had it -more rare

If a female Drosophila that is heterozygous for a recessive X-linked mutation is crossed to a wild-type male, what proportion of female progeny will have the mutant phenotype?

0%

At what stage of the meiotic cell cycle and during what chromosomal configuration does crossing over occur?

at the four strand stage of meiosis, after synapsis of homologous chromosomes, before the end of prophase I

In a healthy male, how many sperm cells would be expected to be formed from (a) 400 primary spermatocytes? (b) 400 secondary spermatocytes?

a) 1600, b) 800

Neurospora crassa was one of the first eukaryotic microbes to be adopted by geneticists as a model organism. It is a haploid fungus (n = 7) found growing on dead vegetation. When an assexual spore germinates, it produces a tubular structure that extends rapidy by tip growth, and throws off multiple side branches. The result is a mass of branched threads called hyphae, which consitute a colony. a) Give two reasons why Neurospora crassa lends itself well to its use as a model organism. b) Two albino strains of Neurospora crassa were isolated. When either one was mated with wild type (pink), it produced ½ albino and ½ wild-type. What can you deduce about the mutations on each of the albino strains?

a) Asexual organisms are easy to study; by being haploid it makes mutations easier to study b)each single gene is a mutation

If two genes assort independently, which categories of ascospore arrangements occur in approximately equal frequencies: parental ditype, nonparental ditype, or tetratype?

dytype or tetratype ??

In a germ-line cell from a human male that is dividing, when do the X and Y chromosomes segregate?

meiosis I anaphase

List four terms used to describe the normal morphologies, with respect to arm ratio, of eukaryotic chromosomes.

metacentric, submetacentic, autocentric, telocentric

A situation where there are more than two alternative forms of a given gene would be called

multiple alleles

A chromosome with a centromere at the very end is called

telocentric

The difference between the homogametic sex and heterogametic sex is that

the heterogametic sex determines the gender of the offspring

Polydactyly is expressed when an individual has extra fingers and/or toes. Assume that a man with six fingers on each hand and six toes on each foot marries a woman with a normal number of digits. Having extra digits is caused by a dominant allele. The couple has a son with normal hands and feet, but the couple's second child has extra digits. What is the probability that their next child will have polydactyly?

1/2

If they live long enough, the penetrance of individuals carrying the Huntington's Disease allele will be what?

100%

A diploid somatic cell from a rat has a total of 42 chromosomes (2n = 42). As in humans, sex chromosomes determine sex: XX in females and XY in males. Reference: Ref 2-1 What is the total number of telomeres in a rat cell in G2?

168

What types of phenotypic ratios are likely to occur in crosses when dealing with a single gene pair where all the genotypic combinations are of equal viability?

1:2:1, 3:1 ??

If a crossover event happened in one half of all tetrads, how many recombinant gametes would be produced?

25%

In an organism with 52 chromosomes, how many bivalents would be expected to form during meiosis?

26

If one is testing a goodness of fit to a 9:3:3:1 ratio, how many degrees of freedom would be associated with the Chi-square analysis?

3 ??

If thymine makes up 15% of the bases in a certain DNA sample, what percentage of the bases must be cytosine?

35%

The genes for mahogany eyes and ebony body are approximately 25 map units apart on chromosome III in Drosophila. Assume that a mahogany-eyed female was mated to an ebony-bodied male and that the resulting F1 phenotypically wild-type females were mated to mahogany, ebony males. Of 1000 offspring, what would be the expected numbers of the following phenotypes:

355,355,125,125 ??

Two organisms, AABBCCDDEE and aabbccddee, are mated to produce an F1 that is self-fertilized. If the capital letters represent dominant, independently assorting alleles, how many different genotypes will occur in the F2?

3^5

There is about as much nuclear DNA in a primary spermatocyte as in ________ (how many) spermatids?

4

The ant, Myrmecia pilosula, is particularly interesting because it carries all its genetic information in a single pair of chromosomes. In other words, 2n = 2. (Males are haploid and have just one chromosome.) For the purposes of this question, assume that a G1 somatic cell nucleus in a female Myrmecia pilosula contains 2 picograms of DNA. How much DNA would be expected in a Metaphase I cell of a female?

4 picograms

Human gametogeneis from one oogonium and one spermatagonium results in how many mature gametes of each?

4 sperm, 1 ovum

Klinefelter syndrome in humans, which leads to underdeveloped testes and sterility, is caused by which chromosomal condition?

47, XXY

How many different kinds of gametes can be produced by an in individual with the genotype AABbCCddEeFf?

8

How many different F2 genotypes would you expect in a cross with four heterozygous gene pairs?

81

Typical ratios resulting from epistatic interactions in dihybrid crosses would be

9:3:4, 9:7

In the fruit fly, Drosophila melanogaster, a spineless (no wing bristles) female fly is mated to a male that is claret (dark eyes) and hairless (no thoracic bristles). Phenotypically wild-type F1 female progeny were mated to fully homozygous (mutant) males, and the following progeny (1000 total) were observed: Phenotypes Number Observed spineless 321 wild 38 claret, spineless 130 claret 18 claret, hairless 309 hairless, claret, spineless 32 hairless 140 hairless, spineless 12 (a) Which gene is in the middle? (b) With respect to the three genes mentioned in the problem, what are the genotypes of the homozygous parents used in making the phenotypically wild F1 heterozygote? (c) What are the map distances between the three genes?

?

Linked genes

?

Two crosses were done to map genes in the dipteran Drosophila melanogaster. Cross 1: Females homozygous for the recessive mutant characters a, b, and c were crossed with wild-type males from a pure-breeding stock. A testcross was then done by taking the F1 females (all wild-type in appearance) and crossing the with triple mutant males (a, b, c) taken from a pure-breeding stock. The following offspring were counted: Phenotype Number a, b, c 280 a + + 77 b + + 23 c + + 125 a, b + 127 a, c + 25 b, c + 75 wild-type 268 1000 Cross 2: A second cross was done, this time involving the same gene c, as in Cross 1, and a new mutant gene d. Females of phenotype "c" were taken from a pure-breeding line and crossed with males of phenotype "d" from another pure-breeding line. In the F1, the females were all wild-type in appearance, while the males were all of the "c" phenotype. The F1 males and females were crossed together to give F2 offspring. The F2 phenotypes occurred in the following numbers: Males: wild-type, 4; c d, 6; c, 43; d, 47. Females: wild-type, 48; c, 52. (a) Using the information from both of the crosses, map these genes. Calculate recombination frequencies and give map distances. Calculate the interference. (b) Give the genotypes, as chromosome diagrams, for the parents and the F1 flies in both crosses, and for the F2 flies in Cross 2.

?

A diploid somatic cell from a rat has a total of 42 chromosomes (2n = 42). As in humans, sex chromosomes determine sex: XX in females and XY in males. What is the total number of chromosomes present in the cell during metaphase I of meiosis?

??

Assume that, regarding a particular gene, one scored 30 second-division ascospore arrangements and 70 first-division arrangements in Neurospora. What would be the map distance between the gene and the centromere?

??

Cytokinesis is

??

During interphase of the cell cycle,

??

How do the daughter cells at the end of mitosis and cytokinesis compare with their parent cell when it was in G1 of the cell cycle?

??

How does epistasis differ from Mendel's principle of dominance?

??

In a three-point mapping experiment, how many different genotypic classes are expected?

??

In the G0 stage of the cell cycle, which of the following is true:

??

Males with an X-linked gene are said to be ______________ for these X-linked genes.

??

Suppose that in sweet cherry a single gene controls fruit color [red (R-) is dominant to yellow (rr)] and a second gene controls bloom time [early bloom (E-) is dominant to late bloom (ee)]. A true breeding tree with red fruit and early bloom is crossed to a tree that has yellow fruit and blooms late. The resulting F1 is selfed to create a population of 500 F2 trees. The segregation of traits in this F2 population is shown below: Red fruit, early bloom: 341 Red fruit, late bloom: 26 Yellow fruit, early bloom: 32 Yellow fruit, late bloom: 101 (i) What is Mendel's Second Law? (ii) Do a Chi Square analysis to determine whether the results conform to Mendel's Second Law. (iii) If the results do not conform to this law, can you come up with an explanation for the lack of conformity?

??

The red kernel color in wheat is caused by the presence of at least one dominant allele from each of two independently segregating gene pairs (e.g., R-B-). Wheat plants with rrbb genotypes have white kernels, and plants with genotypes R-bb and rrB- have yellow kernels. If you cross a plant true breeding for red kernels with a plant true breeding for white kernels, a. what is the expected phenotype(s) and ratios of the F1 plants? b. what are the relative proportions of the phenotypic classes expected in the F2 progeny after selfing the F1 progeny?

??

The sketch above depicts a cell from an organism in which 2n = 2 and each chromosome is metacentric. What stage is does the sketch represent?

??

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 daughter will have hemophilia?

??

When Thomas Hunt Morgan crossed his red-eyed F1 generation flies to each other, the F2 generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?

??

While doing field work in Madagascar, you discover a new dragonfly species that has either red (R) or clear (r) wings. Initial crosses indicate that R is dominant to r. You perform three crosses using three different sets of red-winged parents with unknown genotype and observe the following data: Cross Phenotypes 1 72 red-winged, 24 clear-winged 2 4 red-winged 3 96 red-winged a. What is the most likely genotype for each pair of parents? b. Do you think there are a sufficient number of progeny to support each of your answers in the previous question?

??

n humans, the genetic basis for determining the sex "male" is accomplished by the presence of

??

Assume that the somatic cells of a male contain one pair of homologous chromosomes (e.g., A1 and A2), and an additional chromosome without a homolog (e.g., W). What chromosomal combinations would be expected in the meiotic products (spermatids) of a single primary spermatocyte? (There may be more than one answer.)

A1,W A1,W A2 A2 A1 A1 A2,W A2,W

Given that loci A and B in Drosophila are sex-linked and 20 map units apart, what phenotypic frequencies would you expect in 100 offspring resulting from the following cross? (Assume A and B are dominant to a and b, respectively.) AaBb (cis) female X ab/Y male

AB =? Ab =? aB =? ab =?

Describe at least two different mechanisms for generating sexes in dioecious species.

Chromosomal sex determination; environmental sex determination

List 2 methods that we have discussed used to map human genes.

FISH and synteny testing

Genes contain the instructions for building proteins. Where are those instructions located?

In the order of the DNA bases

Name the single individual whose work in the mid-1800s contributed to our understanding of the particulate nature of inheritance as well as the basic genetic transmission patterns. With what organism did this person work?

Gregor Mendel, Pisum sativum

How do incomplete and co-dominance differ?

Incomplete dominance: neither allele is dominant, both alleles are expressed (pink flowers) Codominance: both alleles in a heterozygote are full expressed with neither being dominant (ex. ABO blood type)

The first stage after which a dividing cell that started as a diploid would be haploid

Meiosis I anaphase

After what meiotic stage (Meiosis I or II) would one expect monads to be formed?

Meiosis II

Assume that you are told that a particular organism, Drosophila, has the XO chromosome complement. You are also told that the autosomal complement is a normal 2n. You know that in humans the XO complement is female determining. Would you be correct in assuming that the Drosophila sex for XO is also female?

No, the chromosomal basis for sex determination in Drosophila and humans is very different.

How does genetic recombination facilitate evolution?

Not only is recombination needed for homologous pairing during meiosis, but recombination has at least two additional benefits for sexual species. It makes new combinations of alleles along chromosomes, and it restricts the effects of mutations largely to the region around a gene, not the whole chromosome

A small part of the human Y chromosome contains the gene that is responsible for determining maleness. What is the name of this gene?

SRY

In the early 1900s, two scientists noted that there were many more genes than chromosome pairs, thus setting the stage for the suggestion that some gene loci might be linked during meiotic processes. Who were these two scientists?

Sutton and Boveri

Human blood types are an example of codominance because

The A and B alleles both express equally in individuals with both alleles.

Which of the following statements about homologous chromosomes are true?

They occur together in diploid cells

Microscopy to look at a cell's chromosomes is often done when the cell is in mitotic metaphase. For example, karyotypes that extract chromosomes from a single cell and photograph them to look for abnormalities are done on metaphase, rather than interphase, cells. Why?

This is when sister chromatids are still attached

The Protenor mode of sex determination is the

XX/XO scheme.

The Lygaeus mode of sex determination is the

XY/XX

Extensive pedigree analysis on a characteristic shows all of the following: •only males are affected. •affected fathers always pass the trait to sons. What does this pedigree indicate:

Y linked

Is it possible for two different genes located on the same chromosome to assort independently? Explain your answer.

Yes, independent assortment can occur. If they are far enough, it is likely there will be at least one crossover occurence between the 2 genes.

What is the probability of rolling two six-sided dice and obtaining the following numbers: a) 2 and 3? (enter answer in box 1) b) 6 and 6? (enter answer in box 2) c) at least one 6? (enter answer in box 3) d) Two of the same number (two 1s, or two 2s, or two 3s, or two 4s etc.)? (enter answer in box 4) e) An even number on both dice? (enter answer in box 5) f) An even number on at least one dice? (enter answer in box 6) Enter all answers as fraction (e.g. 1/3 ). When possible use the simpliest form (e.g. simplify 2/6 to 1/3)

a)1/18 b)1/36 c)11/36 d)1/6 e)1/4 f)3/4

Assume that a man who carries an X-linked gene has children. Assuming normal meiosis and random combination of gametes, the man would pass this gene to

all of his daughters ??

Phenotypically, what two general categories of offspring did Sturtevant and Morgan observe in the F2 generation of their fly crosses?

body color and wing size

Assume that a cross is made between AaBb and aabb plants and that all the offspring are either AaBb or aabb. These results are consistent with the following circumstance:

complete linkage

Two- and three-factor testcrosses can both be used to _____________ and _____________.

determine genotype and map gene loci

The contribution of Gilbert and Sanger to modern genetics was to

develop a method for sequencing DNA

Mice homozygous for mutations in one gene exhibit polydactyly (i.e. extra toes) while in another gene (limb deformity), homozygous mutants lack all parts of the limb below the wrist. A mutant that is doubly homozygous for extra toes and limb deformity mutations will NOT exhibit polydactyly because it is missing the distal limbs, where the toes are located. This type of genetic relationship is called

epistasis

The complete genetic makeup of any organism is its

genome

0.1% frequency of recombination is observed

in genes located very close to one another on the same chromosome

In a Chi-square test, as the value of the (chi)2 increases, the likelihood of rejecting the null hypothesis

increases

The attachment point on the chromosome for spindle microtubules is the

kinetochore ??

The phenomenon in which one crossover increases the likelihood of crossovers in nearby regions is called

negative interference

For an individual with the XXY chromosomal composition, the expected number of Barr bodies in interphase cells is

one

Choose the answer that lists--in order of appearance--all the cell types expected to be formed during oogenesis.

oogonium, primary oocyte, secondary oocyte and first polar body, ootid and second polar body

In a Chi-square analysis, what condition causes one to reject (fail to accept) the null hypothesis?

p less than 0.05

In studies of human genetics, usually a single individual brings the condition to the attention of a scientist or physician. When pedigrees are developed to illustrate transmission of the trait, what term does one use to refer to this individual?

proband

The fundamental Mendelian process that involves the separation of contrasting genetic elements at the same locus would be called

segregation

What is the outcome of synapsis, a significant event in meiosis?

side-by-side alignment of homologous chromosomes