Exam 2 Flashcards
Why do we use pedigrees?
Geneticists often use pedigrees to study the inheritance of characteristics in humans
How could you distinguish between an autosomal recessive trait with higher penetrance in males and an X-linked recessive trait?
X-linked recessive traits are only passed to sons from mothers, not from fathers
How do linked genes behave during meiosis?
Linked genes travel together in meiosis, eventually arriving at the same destination ( same gamete), and are not expected to assort independently
How does crossing over affects recombination?
Crossing over takes place in meiosis and leads to recombination
What are the three models of DNA replication?
Conservative, Semi-conservative and dispersive
What are the three main things needed for DNA replication?
Parental DNA, enzymes, and nucleotide triphosphate
What are the stages of DNA replication?
Initiation, elongation and termination
The Central Dogma: How does information flow?
DNA to mRNA to protein
What does it mean to say the code is “degenerate”?
some amino acids are specified by more than one codon
What is the addition of a long chain of adenine residues to the 3’ end of the transcript called?
3’ poly-A tail
The complete set of chromosomes possessed by an organism is called a
Karyotype
Which type of chromosome mutation results in a chromosome segment that is turned 180 degrees?
Inversion
The centromere is at or very near the end in which type of chromosome?
Acrocentric
Which type of chromosome mutation INCREASES the amount of genetic material?
Duplication
What are the four basic types of chromosome rearrangements
deletion, inversion, duplication and translocation
which of the following is NOT a rearrangement that causes chromosomal mutations?
transformation
The centromere is located approximately in the middle of which type of chromosome?
Metacentric
Which type of chromosome mutation DECREASES the amount of genetic material?
deletion
If a deletion occurs in a gene that encodes DNA polymerase I and no functional DNA polymerase I is produced, what will be the MOST likely consequence of this mutation?
The DNA strands would contain pieces of RNA
True or False: Some DNA polymerases have the ability to function in DNA repair mechanisms
True
Which of the following enzyme and function pairs is incorrectly matched
DNA helicase; rewinding and reforming the DNA double helix as the replication terminates
What type of synthesis occurs on the leading strand?
Continuous
Okazaki fragments are found in all the following EXCEPT in
The leading strand
What is the function of DNA ligase?
Connects Okazaki fragments by sealing nicks in the sugar-phosphate backbone
Which of the following typically only have in origin of replication?
prokaryotes
Which activity is NOT associated with DNA polymerases?
Ability to synthesize a DNA from scratch without a primer
Meselson and Stahl showed that DNA is replicated by a
semiconservative system
______ are tandemly repeated DNA sequences located at the ends of eukaryotic chromosomes
Telomeres
What is a proband?
a person serving as the starting point for the genetic study of a family
One disease that arise from a Robertsonian translocation between two chromosomes
Down syndrome between chromosome 21 and 14
What is the start codon in Eukaryotes?
AUG
Gametes with new combinations of alleles are called
recombinant gametes
The arrangement, in which wild-type alleles are found on one chromosome and mutant alleles are found on the other chromosome is known as
coupling or cis configuration
The arrangement, in which each chromosome contains one wild type and one mutant allele is called
repulsion or trans configuration
What conditions can geneticist often use pedigrees to study inheritance and characteristics of humans?
- autosomal dominant traits
- autosomal recessive traits
- X-linked recessive traits
- X-linked dominant traits
- Y-linked traits
True or False: autosomal dominant traits appear equally in males and females?
True, affected people have at least one affected parent
True or False: autosomal recessive traits tend to skip generations
True, traits more likely to appear among progeny of related parents
True or False: An affected male does not pass the trait to his sons in an X-linked recessive trait?
True, but an affected male can pass the allele to his daughter who will be unaffected
Pedigree characteristics Y-linked traits?
- only males are affected
- passed from father to all sons
- does not skip generations
Autosomal recessive traits often appear in pedigrees in which there have been consanguine mating because …
these traits appear only when both parents carry a copy of the gene for the trait, which is more likely when the parents are related
What is a concordant trait?
A trait shared by both members of a twin pair
What are the two types of twins?
- monozygotic and dizygotic
A trait exhibits 100% concordance in both monozygotic and dizygotic twins. What conclusion can you draw about the role of genetic factors in determining differences in the trait
both genetic and environment factors are important
Reasons for seeking genetic counseling
- a person knows of a genetic disease in the family
- An older woman becomes pregnant or wants to become pregnant
- A couple experiences difficulties achieving a successful pregnancy
- a known genetic disease in the family
What is a pedigree?
a pictorial representation of a family history, essentially a family tree that outlines the inheritance of one or more characteristics
In a pedigree a male is pictured as..
square
In a pedigree a female is pictured as…
circle
In a pedigree a unknown sex is pictured as…
diamond
In a pedigree an unaffected person is pictured as..
uncolored
In a pedigree an affected person is pictured as..
colored in
In a pedigree a carrier of the gene but does not have the trait is pictured as…
a colored circle in the middle
In a pedigree an asymptomatic carrier is pictured as…
having a line go through it
In a pedigree a deceased person is pictured as…
a line going across it
Waaredenburg syndrome
-inherited as an autosomal dominant trait
- characterized by deafness, fair skin, visual problems and a white forlock
True or False; autosomal dominant traits tend to skip generations
False, they do not skip generations because they only require the inheritance of one dominant allele to express the phenotype
What is an example of an X-linked recessive trait?
Hemophilia
Autosomal recessive traits often appear in pedigrees in which there have been consanguine mating because these traits…
Appear only when both parents carry a copy of the gene for the trait
Autosomal recessive traits
- usually appear in both sexes with equal frequency
- tends to skip generations
- affected offspring are usually born to unaffected parents
- When both parents are heterozygous, approximately 1/4 of the offspring will be affected
- appears among the children of consanguineous marriages
Autosomal dominant trait
- usually appears in both sexes with equal frequency
- both sexes transmit the trait to their offspring
- Does not skip generations
- affected offspring must have an affected parent unless they possess a new mutation
- when one parent is affected (heterozygous) and the other parent is unaffected, about half the offspring will be affected
- unaffected parents do not transmit the trait
X-linked recessive trait
-Usually more males than females are affected
- affected sons are usually born to unaffected mothers; thus, the trait skips generations
- About half of a carrier (heterozygous) mother’s sons are affected
- Never passed from father to son
- All daughters of affected fathers are carriers
X-linked dominant trait
- both females and males are affected; more females than males are affected
- does not skip generations
- affected sons must have an affected mother; affected daughters must have an affected mother or father
- affected fathers pass the trait to all their daughters
- affected mothers (if heterozygous) pass the trait to half of their sons and half of their daughters
Y- Linked traits
- only males are affected
- passed from father to all sons
- does not skip generations
How could you distinguish between an autosomal recessive trait with a higher penetrance in males and an X-linked recessive trait?
X-linked recessive traits are only passed to sons from mothers, but not from fathers
Dizygotic twins
- two separate eggs are fertilized by two different sperm
- produce genetically distinct zygote
- influenced by heredity and genetic factors
monozygotic twins
- A single egg is fertilized by a single sperm
- Splits in early development into two separate embryos
- genetically identical
- 100% genes in common
Discordant trait
Only one member of the twin pair has the trait
Concordance
the percentage of twin pairs that are concordant for a trait
Genetic counseling
Provides info related to hereditary conditions
Asthma caused by genetics&environment : Twin test
- Monozygotic: 65%
- Dizygotic: 37%
Complications in interpreting genetic test
- some diseases caused by multiple mutations
- incomplete penetrance
- environmental factors
What is GINA?
Genetic information nondiscrimination act
True or False: Pattern baldness is a hereditary trait
True
Genes located close together on the same chromosome are called…
linked genes
Linked genes
- travel together in meiosis, eventually arriving at the same destination (same gamete)
- Are not expressed to assort independently
nonrecombinant gametes
Gametes that contain only original combinations of alleles that were present in the parents
DNA recombination
the exchange of genetic material either between multiple chromosomes or between different regions of the same chromosome
Recombination
The sorting of alleles into new combinations
Recombination frequency calculation
Number of recombinant progeny
___________________________________ X 100%
Total number of progeny
True or False: crossing over takes place in prophase I of meiosis
True
True or False: A two-strand double crossover between two linked genes does not produce nonrecombinant gametes
False, a two-strand double crossover between two linked genes produces ONLY nonrecombinant gametes
Middle Locus Rules
- write all possible progeny
- determine&highlight the double crossover progeny
- Place Loci in order so each has a chance to be in the middle
- Flip the middle locus
- which outcome matches the double progeny is the middle locus
A three-point test cross is carried out btw three-linked genes. The resulting nonrecombinant progeny are s+r+c+ and src, the double crossover progeny are src+ and s+r+c. What is the middle locus
It’s C: but girl u need to show work
What is RFLPs
Restriction fragment length polymorphism
What is it when the centromere is at or very near the end of the chromosome?
telocentric
Submetacentric
the centromere is displaced toward one end, creating a long arm and a short arm
Aneuploidy
alters the number of chromosomes
Polyploidy
One or more complete sets of chromosomes are added
Chromosome duplication
a segment of the chromosome is duplicated
Chromosome deletion
A segment of the chromosome is deleted
Chromosome inversion
A segment of the chromosome is turned 180
Chromosome translocation
A segment of a chromosome moves from one chromosome to a non-homologous chromosome or to another place on the same chromosome
pseudodominance
indication that one of the homologous chromosomes has a deletion
haploinsufficient
when a single copy of a gene is not sufficient to produce a wild-type phenotype
Paracentric inversions
Inversions that do not include the centromere, such as AB.CFEDG
(Para meaning “next to”)
Pericentric inversions
inversions that include the centromere, such as ADC.BEFG
(Peri meaning “around)
nonreciprocal translocation
genetic material moves from one chromosome to another without any reciprocal exchange
robertsonian translocation
the long arms of two acrocentric chromosomes become joined to a common centromere through translocation, generating a metacentric chromosome with two long arms and another chromosome with two very short arms
Causes of aneuploidy
- deletion of centromere during mitosis and meiosis
- nondisjunction during meiosis and mitosis`
Nullisomy
type of aneuploidy
- the loss of both members of a homologous pair of chromosomes
- represented as 2n-2
- nullisomic zygote has 44 chromosomes
Monosomy
type of aneuploidy
- the loss of a single chromosome
- represented as 2n-1
- monosomic zygote has 45 chromosomes
Trisomy
type of aneuploidy
- the gain of a single chromosome
- represented as 2n+1
- trisomic zygote has 47 chromosomes
Tetrasomy
type of aneuploidy
- the gain of two homologous chromosomes
- represented as 2n+2
- tetrasomic zygote has 47 chromosomes
Trisomy 21
- down syndrome
- 75% random nondisjunction in egg formation
- the translocation of part of chromosome 21 to another chromosome results in familial down syndrome
Nondisjunction
failure of normal chromosome separation during nuclear division leading to abnormal chromosomes in daughter cells
Trisomy 18
- Autosomal Aneuploid
- Edward Syndrome
- 1/8,000 births
Trisomy 13
- Autosomal Aneuploid
- Patau Syndrome
- 1/ 15,000 births
Trisomy 8
- Autosomal Aneuploid
- 1/ 25,000 - 1/50,000 births
True or False: the frequency of aneuploidy increases with maternal age
True, most cases of down syndrome and other types of aneuploidy in humans arise from maternal nondisjunction
Autopolyploidy
Caused by accidents of mitosis or meiosis that produce extra set of chromosomes, all derived from a SINGLE species
Allopolyploidy
arises from hybridization between two species; the resulting polyploid carries chromosome sets derived from two or more species
Significance of polyploidy
- increase in cell size
- larger plant attributes
- evolution: many gives rise to new species
Species A has 2n=16 and species B has 2n=14. How many chromosomes would be found in an allotriploid of these two species
2n= 16 2n=14
2n/2= 16/2 2n/2= 14/2
n= 8 n= 7
1n= 8 1n=7
SWITCH
8+14= 22 7+18= 23
ANSWER: 22 or 23
DNA Replication
- the process by which the genetic material is copied
- The orginal DNA strands are used as templates for the synthesis of new strands
- occurs quickly and accurately and the appropriate time in the life of the cell
True or False: Genetic information must be accurately copied every time a cell divides
True, replication HAS TO BE extremely accurate
- one error = million base pairs would result in 6,400 mistakes every time a cell divides! This would be catastrophic!
Conservative Replication
- Both strands of parental duplex remain intact
- new DNA copies consist of all new molecules
Semiconservative replication
Daughter strands each consist of one parental strand and one new strand
Dispersive replication
New DNA is dispersed throughout each strand of both daughter molecules and replication
Where does Translation occur?
Cytoplasm
Where does transcription occur?
Nucleus
What is RNA polymerase?
Enzyme that unzips double stranded DNA and synthesizes the formation of mRNA
What is a codon?
3 base sequence of mRNA that codes for a specific amino acid
What is an anticodon?
Set of three ribonucleotides complementary to a specific mRNA codon sequence
Can more then one ribosome translate an mRNA strand at once?
A single mRNA can be translated simultaneously by multiple ribosomes
How did Meselson and Stahl distinguish between old and new DNA
Used two isotopes of nitrogen, 14N and 15N
Conclusion of the Meselson and Stahl experiment?
DNA replication in E.Coli is semiconservative
How many bands of DNA would be expected in Meselson and Stahl’s experiment after two rounds of conservative replication?
Two Bands
The newly synthesized DNA strand is _______ and ________ to the template strand
antiparallel and complementary
Lagging Strand
Newly made strand that undergoes discontinuous replication
Primers are synthesized where on the lagging strand?
At the beginning of every Okazaki fragment
Which bacterial enzyme removes the primers?
DNA polymerase I
What is the direction of transcription?
5’ to 3’
What is a holoenzyme?
Core enzyme & sigma factor
Upstream?
left side of promoter
Downstream?
Right side of promoter
True or false: transcription occurs constantly?
False, there will be pauses because of features of the DNA and RNA
Does transcription stop at a “stop” codon?
No
Eukaryotic Transcription
- 3 different RNA polymerases instead of 1
- nucleosome structure
- promoters
What is a mutagen?
Any agent that increases the number of mutations above background level radiation chemicals
