Genetics Exam #3

male pattern baldness

hair loss of men; using linkage analysis, the geneticists discovered _______ ________ ___________ was associated with SNPs on the p arm of chromosome X

adrogen-receptor gene

The SNPs associated with male pattern baldness were physically linked to an __________ ___________ _______ that binds make sex hormones

linkage groups

groups of genes that are physically connected

patterns of inheritence

because chromosomes are inherited from two parents, the linkage groups could have different alleles that complicate what?

crossing over

Meiotic ______ ______ is the primary process that breaks up linkage groups

recombination

recombination of alleles, not genes

gene far apart

may appear to independently assort because of crossing over

genes close together

will not assort independently

Bateson and Punnett

discovered two genes that did not assort independently

flower color and pollen shape

in 1905, Bateson and Punnett conducted a cross in sweet pea involving what two different traits?

not independent

Bateson and Punnett suggested that the transmission of the two trait from the parents are _____ ___________; however, they did not realize that the coupling is due to the linkage od the two genes on the same chromosome

Thomas Hunt Morgan

observed more F2 nonrecominant phenotypes than recombinant and hypothesized that all three genes must be located on the X chromosome and transmit together

1930s

When was the race between Harriet Creighton and Barbara McClintock vs Curt Stern over proving recombination was the result of physical chromosomal exchange?

Harriet Creighton and Barbara McClintock

To obtain direct evidence that genetic recombination is dur to crossing over used two linked genes which yielded parental and recombinant offspring?

unusual structural features

Creighton and McClintock observed the chromosomes in the parents and offspring microscopically. Parental chromosomes had some ______ _______ _______. They wanted to see if there was a correlation between the occurrence of recombinant offspring and microscopically observable exchange in segment of homologous chromosomes

genetic mapping

purpose of _____ _____ is to determine the linear order of linked genes along chromosomes

relative distances between linked genes

What do genetic maps estimate?

distance between genes

What are recombination frequencies correlated with?

map distance =

(# of recombinant offspring / total # of offspring) x 100

map units

mu and are equivalent to 1% recombination frequency

testcross

mating between an individual that is heterozygous for multiple genes and one that is homozygous recessive for the same genes

50% recombination

a testcross is expected to yield a maximum of ____ _______ offspring, when more than 50 mu's apart, they follow the laws of independent assortment

different linkage groups

If genes exhibit 50% recombination then the most that can be said is that they belong to _____ ______ ____, either on different chromosomes or far apart on the same chromosome

double cross over events

Distance between genes that are far apart on the same chromosome tend to be underestimated because of what?

coupling

one chromosome contains both wild-type alleles, one chromosomes contains both mutant alleles

repulsion

wild-type alleles found on opposite chromosomes

gene order

three-factor crosses can also yield additional information about map distance and what?

middle gene

double crossover recombinants only have what gene altered?

parental nonrecombinants

occurs most frequently and are identified by the highest TWO numbers

double crossover recombinant

occurs least frequently and are identified by the lowest two numbers

Interference

crossovers are not independent events because one crossover inhibits another

positive interference

the first crossover decreases the probability that a second crossover will occur nearby

coefficient of coincidence

In I=1-C, what is C

among species

2x more recombination in humans than rodents

among chromosomes

Chromosomes 21 and 22 have highest recombination rates; 2 and 4 have the lowest

recombination hotspots "fragile sites"

• Appear to be associated with trinucleotide repeats

• In humans, tend to be near, but not in, active genes

• Areas near centromeres often have reduced rates

sequences do not solely determine hotspots

-females tend to have larger recombinant than males

-chimps and humans have very different hotspots

females make one egg and it has to happen to the egg to be recombinant

Natural selection has selected for mothers to have higher

recombination rates, why?

fitness advantage

recombination rate is a heritable phenotype with a clear ____ _________

gamete formation fails

crossing over MUST occur or what happens

reasons genetic maps are useful

1. Understand the overall complexity and genetic organization of a particular species

2. Help molecular geneticists to clone genes

3. Improve our understanding of the evolutionary relationships among different species

4. Can be used to diagnose and treat inherited diseases

5. Can help predict disease inheritance

6. Can improve agricultural strains through selective breeding programs

synteny

genes that are physically located on the same chromosome

syntenic blocks

th evolutionary conservation of syntenic genes; genes that have remained together during evolution

genetic diversity

The range of genetic material present in a gene pool or population of a species.

deletions

<100%, the loss of a chromosomal segment

duplications

>100%, the repetition of a chromosomal segment compared to the normal parent chromosome

inversions

100%, a change in the direction of part of the genetic material along a single chromosome

Translocations

100%, a segment of one chromosome becomes attached to a different chromosome

single or double breaks

a chromosomal deletion occurs when a chromosome breaks and a fragment is lost, what kind of breaks can occur?

visibly shorter

large deletions are easily detected because chromosomes are ______ _______

loops out

during paring and tetrad formation, normal chromosome _____ ______

microtubules

effects of deletion: if deletion includes centromere, chromosomes will not attach to _____ and will be lost

lethal

effects of deletion: many deletions are _____ in the homozygous state

gene dosage

effects of deletion: individual heterozygous for a deletion may cause imbalances in _____ ________

pseudodominance

effects of deletion: expression of a normally recessive gene

Haploinsufficiency

when single copy of a gene is not sufficient enough to produce wild-type phenotype

abnormal events during recombination

a chromosomal duplication is usually cause by ______ _____ during ______.

-repetitive sequences can cause misalignment between homologous chromosomes

-if misaligned crossover occurs, nonallelix homologous recombination results

less harmful

duplications tend to have ____ ________ effects than deletion of comparative size; all genes are still present

duplication

individuals can be homozygous or heterozygous for a _________

prophase

problems arise in heterozygous duplications in chromosome pairing in ______

pericentric inversion

inversion that includes the centromere

paracentric inversion

inversion that does not include the centromere

phenotypic consequences

most inversions have NO _____ _____

true

T or F: it is rare for inversions to alter the phenotype of an individual

break point effect

An inversion break point occurs in a vital gene

position effect

a gene repositioned in a way that alters gene expression

reciprocal translocation

two-way exchange of segments

Simple (nonreciprocal) translocation

genetic material moves from one chromosome to another without reciprocal exchange

Robertsonian translocation

long arm of two acrocentric chromosomes become joined, creating chromosome with two long arms and one with two short arms

translocation cross

the structure that is formed when the chromosomes of a reciprocal translocation attempt to synapse during meiosis. This structure contains two normal (nontranslocated chromosomes) and two translocated chromosomes. A total of eight chromatids are found within the cross.

nonviable

gametes resulting from adjacent-1 and adjacent-2 segregation are ____ because come genes are present in two copies whereas others are missing

alternate segreation

centromere of homologous chromosomes goes to opposite poles. only mode that leads to balance

adjacent-1 segregation

horizontal division which leads to 4 genetically unbalanced gametes

adjacent-2 segregation

vertical divisions which leads to 4 genetically unbalanced gametes

simple translcations

in _____ ______ the transfer of genetic material occurs in only one direction

phenotypic abnormalities or lethality

nonreciprocal translocations are associated with ____ _______ or ______

1 in 900 births

robertsonian translocation are the most common rearrangement in humans occurring how much?

endogenous

Evidence suggests the Env gene has become ______ in humans and repurposed

mutations

vertically inherited genes rely on _______ for genetic diversity

horizontal gene transfer

the transfer of a genetic element from one organism to another within the same generation

E. coli

most of what we know about horizontal gene transfer comes from the bacteria called what?

directionality

horizontal transmission has ________; there is a donor and recipient

nuceloid

prokaryotes carry their genome as a _______ -a single circular chromosome

plasmids

SOME bacteria harbor extra-chromosomal genetic elements know as what?

transformation

bacterial cells acquire and incorporate DNA from the environment

competent cells

are capable of acquiring and incorporating DNA from the environment

rare

competent bacteria species are what?

one strand is digested and another is produced then incorporated into double crossover

during the transformation process, what is happening?

*

What is the benefit of transformation?

Why is transformation widely used method in genetics and microbiology labs?

plasmids; selective gene is added

Microbiologist have developed ways to create competent cells, rather than requiring the bacterium to successfully establish double crossover most lab transformations use _______ and to ensure transformation was successful and have the desired gene what is added?

ampR

gene on plasmid; if bacterium has this plasmid, will be able to grow on agar with ampicillin. If does not have plasmid, will not grow on agar with amp.

artificial selection

imposes an artificial fitness advantage to organisms with traits that humans desire; example of strong, positive selection

conjugation

direct transfer of DNA from the donor to the recipient through physical contact

pilus

the donor typically transfers the F+ plasmid through what?

self-transmissible

the plasmid can have all the genes it needs to be what?

mobilizable plasmid

may depend on another F factor to form a pilus

cytoplasm or nucleid

the transmitted plasmid either float freely in _____ or will integrate into the ______

transduction

foreign DNA is introduced to a cell by a viral vector

Virus Life Cycle

1. Attachment

2. Entry

3. Synthesis

4. Assembly

5. Release