GENETICS EXAM II STUDY GUIDE

•What is Genetic Counseling?

-Genetic counseling gives you information about how genetic conditions might affect you or your family. The genetic counselor collects your family health history. They use this information to determine how likely it is that you or your family member has a genetic condition.

How many nucleotides per turn or 3.4nm are there in B-DNA?

10 nucleotides

C and G have how many bonds, whereas A and T have how many bonds?

3;2

A recombination frequency of 5% translates to what distance on a genetic map?

5 m.u.

A genetic cross with two genes produces 400 offspring, and 20 of them have recombinant phenotypes. What is the recombination frequency for this cross?

5%

Which statement best describes linkage? A) It is a condition in which two or more genes do not show independent assortment. B) It is a condition that occurs in many types of organisms but not in humans because we do not produce sufficient numbers of offspring. C) It is a condition where a heterozygous individual makes only one type of gamete. D) It is a condition where two genes are located on separate chromosomes. E) It is a condition where one parent in a cross is homozygous for two or more genes and the other parent is heterozygous.

A) It is a condition in which two or more genes do not show independent assortment.

When two genes are linked but quite far apart, their estimated map distance, based on recombination frequencies, is often an underestimation of their true map distance. What is the explanation for this underestimation? A) Some double crossover events go undetected since they do not lead to recombinant progeny. B) There will be few or no double crossovers occurring so that more nonrecombinant progeny are produced. C) One of the genes is lethal when homozygous which reduces the recombination frequency. D) There will be more single crossover events counted than actually have occurred so the recombination frequencies will be reduced. E) The genes are located on different pairs of homologous chromosomes.

A) Some double crossover events go undetected since they do not lead to recombinant progeny.

In a testcross involving two heterozygous genes, equal numbers of recombinant and nonrecombinant progeny are produced. From this result, what can be concluded? A) The genes are not linked. B) The genes are linked, and there is some crossing over between them. C) The genes are located very close to each other. D) The genes are linked, but there is no crossing over between them. E) One of the two genes is lethal when homozygous.

A) The genes are not linked.

A male affected with an X-linked dominant trait will have what proportion of offspring affected with the trait?

All daughters and no sons

Which statement about chromosome inversions is correct? A) Chromosome inversions lead to an increase in crossovers. B) Chromosome inversions flip a segment of a chromosome 180 degrees. C) Chromosome inversions do not affect gene expression. D) Chromosome inversions can reduce the number of chromosomes in a cell.

B) Chromosome inversions flip a segment of a chromosome 180 degrees.

Which statement about aneuploidy is true? A) Aneulploidy is a change in number of chromosome sets. B) One form of aneuploidy is a loss of both members of a homologous pair of chromosomes. C) Most autosomal aneuploids develop normally and have a normal life span. D) The rarest aneuploidies in humans are those of the sex chromosomes.

B) One form of aneuploidy is a loss of both members of a homologous pair of chromosomes.

___________ is the most common secondary structure

B-DNA

Which statement about Down syndrome is true? A) The primary cause for Down syndrome is the Robertsonian translocation. B) Down syndrome never runs in the family, as it is based on a random aneuploidy event. C) Trisomy of chromosome 21 is well tolerated enough to give rise to fully‑developed individuals. D) The probability of a child having Down syndrome does not correlate with maternal age.

C) Trisomy of chromosome 21 is well tolerated enough to give rise to fully‑developed individuals.

Three‑point testcrosses are often used to map genes. The two least frequent classes from such crosses usually represent which types of progeny? A) one nonrecombinant class and one single‑crossover class of progeny B) nonrecombinant progeny C) double‑crossover progeny D) single‑crossover progeny E) half the nonrecombinant progeny

C) double‑crossover progeny

True or False: Pedigree analysis is only for humans

False: in class we looked at example of pedigrees in California condors, FL panthers, Mexican wolf

X-linked recessive

Female is usually an unaffected carrier; an affected male does not pass the trait to his sons but can pass the allele to a daughter who is unaffected and it passes to her sons who are affected. X linked recessive traits appear more frequently in males so ONLY SONS of an affected or carrier Females will be affected

Frank has Klinefelter syndrome (47, XXY). His mother has normal skin, but his father has anhidrotic ectodermal dysplasia, an X‑linked condition where the skin does not contain sweat glands. Frank has patches of normal skin and patches of skin without sweat glands. Frank received the mutant chromosome from his _____________. Nondisjunction occurred in his __________during the ___________ meiotic division

Frank received the mutant chromosome from his father. Nondisjunction occurred in his father during the 1st meiotic division.

Match the definitions to the appropriate terms that describe the number of chromosomes. Terms: Monosomic Haploid 𝑛=1 Definitions: a single unpaired copy of each chromosome only one copy of a specific chromosome a genome composed of one unique chromosome

Haploid - a single unpaired copy of each chromosome Monosomic - only one copy of a specific chromosome 𝑛=1 - a genome composed of one unique chromosome

______________ inherited as an X-linked recessive trait in the european royal families

Hemophilia

What are some challenges in human genetic studies

I) Controlled mating's are unethical: e.g, no testcross is possible to determine if a dominant phenotype is of homozygous dominant or heterozygous genotype II) Long generation time: ~20 years, and 40 years to get F2 III) Small number of off spring: Phenotypic ratios not clear with small sample sizes, conceals probability patterns

B-DNA forms ______ and ________ which is necessary for protein binding

Major and minor grooves

What are the requirements of genetic material

Must store a Large amount of info- instructions for all traits and function Must encode the phenotypes -how genetic info is expressed Must be replicated accurately-high fidelity must have capacity to vary- species and individuals differ

Y-linked traits appear _________________

Only in males; all male offspring of an affected male are affected

During meiosis, errors occur during chromosome replication. Which term describes the rearranging of genetic material between nonhomologous chromosomes without a net loss or gain of genetic material?

Translocation

______________________ affect both males and females. Affected males must have affected mothers (unless the males possess a new mutation), and they pass the trait to all their daughters.

X-linked dominant traits

definition of euploidy

a complete chromosome set or an exact multiple of the haploid chromosome set

In X-linked dominant affected females (if Heterozygous) pass the trait on to ____________________ and _______________________

about half of their sons and half of their daughters

X linked dominant: Affected ________pass the trait on to _____________and ___________

affected males pass the trait on to all their daughters and non of their sons

in X-linked dominant _____________ have an affected mother

all affected males

Red‑green color blindness is a human X‑linked recessive disorder. The normal allele, XB, is dominant to the mutant allele, Xb. Jill has normal color vision, but her father is color blind. Jill marries Tom, who also has normal color vision. Jill and Tom have a daughter who has Turner syndrome and is color blind. How and from whom did the daughter inherit color blindness?

an ovum carrying Xb followed by fertilization by sperm from a paternal nondisjunction event

Nystagmus can be acquired of congenital: list reasons how for both

aquired - drugs/medication -stroke -head trauma Congenital •a.k.a infantile (since birth) •Unaware •Inherited (1/1500 births) •Several genes/mutations identified

Waardenburg syndrome is ___________ _____________ trait and characterized by ___________, _________ __________,_________ __________, and _______ ________.

autosomal dominant trait and characterized by deafness, fair skin, visual problems, and white forelock

Which structure forms as a result of a crossover between two paired chromatids in which one chromatid has the normal gene order and the other has a paracentric inversion?

dicentric bridge

X-linked dominant traits _______________________generations

do not skip

Autosomal dominant traits usually appear_________________, _____________________ and _____________________

equal in males and females, the unaffected people do not transmit the trait, affected people have at least one affected parent

Autosomal Recessive traits usually appear

equally in males and females, tend to skip generations and are more likely to appear among progeny of related parents

Two brothers have X‑linked red-green colorblind vision, and their parents have normal color vision. The first brother's karyotype is 47,XXY (Klinefelter syndrome), and the second brother's karyotype is 46,XY. In which parent and in what cell division phase did the first brother's chromosomal nondisjunction occur? Assume no recombination.

in the mother in meiosis II

The spread of a complete metaphase chromosome set presented for diagnostic purposes is called a _________________.

karyotype.

Which term describes the process of sister chromatids not separating at the centromere during cell division?

nondisjunction

Failure to separate for homologous chromosomes or sister chromatids is referred to as .

nondisjunction.

Dominant mutations are _______________ - assume individuals carrying a dominant/disease are _______________ - what is the exception to this?

often lethal when homozygous - assume individuals carrying a dominant/disease are heterozygotes - exception is X-linked dominant in males

Consider the diagram. AB ∙ CDEFG > AB ∙ CFEDG Which type of inversion is presented in the diagram?

paracentric

Geneticists often use ____________ to study the inheritance of characteristics in humans - it can give value clues to the inheritance pattern

pedigrees

Most traits are __________ - assume people marrying into a family are _____________ for the wild type allele unless other evidence available

rare - homozygous

when examining a pedigree be sure to ___________________

rule out other possibilities

Additional copies of a gene ___ cause cellular problems.

sometimes

Parthenogenesis in California condors. this parthenote condor gets______________________________________________ ________________________________________________________

this parthenote condor gets ALL ITS ALLELES FROM MOTHER ONLY

Of all cases of primary Down syndrome, 92% is due to of Chromosome 21.

trisomy

B-DNA is stable in _____and _____ - __________________helix which is ______

water and general physiological conditions - right-handed helix (clockwise direction)

X-linked dominant traits

•Appears in both males and females; often more females •Doesn't skip generations •Suspect if only daughters of an affected father are affected •Rule out X-linked recessive if any affected daughters are born to affected mothers and non-affected fathers

•Autosomal Recessive trait

•Assume new carriers may marry into family. •Equal number of affected males and females •Affected individuals often born to unaffected parents •Look for skipped generations •For rare recessive alleles, new carriers marrying into family is uncommon. •Higher possibility of trait appearing, however, if inbreeding

Autosomal Dominant Trait

•Equal number of affected males and females, and both sexes transmit trait •Affected individual has at least one affected parent •Trait appears in every generation •Unaffected parents do not transmit trait

Pedigree is defined as a

•Family tree that outlines the inheritance of one or more characteristics

what is Nystagmus

•Nystagmus is an involuntary rhythmic side-to-side, up and down or circular motion of the eyes that occurs with a variety of conditions

Proband is defines as a

•Person from whom the pedigree is initiated

Y-linked Trait

•Suspect if all males born to affected fathers also affected •Only males affected

X-linked Recessive trait

•Suspect if more males affected •Affected sons usually born to unaffected mothers, so can skip a generation •Never passed from father to son •Rule out X-linked dominant if any daughters of an affected father don't have disease