Chapter 2 Lecture Flashcards
(88 cards)
1
Q
Chromosomes come in how many pairs
A
23
2
Q
Genes
A
30,000
3
Q
How many base pairs are there
A
3 billion
4
Q
Each gene makes about
A
3 protiens
5
Q
Each chromosome contains how many bases… ?
A
50 million to 300 million base pairs.
6
Q
Describe DNA
-what does it stand for, what is the structure, prymiades, purines? what does it make? where?
A
Deoxyribose Phosphate molecule Four nitrogenous bases: Pyrimidines: cytosine and thymine Purines: adenine and guanine Double helix model Nucleotide
-in the CYTOPLASM, makes proteins
7
Q
what are proteins?
what are they composed by?
A
One or more polypeptides
Composed of amino acids
Twenty amino acids
Directed by sequence of bases (codons)
8
Q
describe the process of DNA replication
A
Step 1 - Untwisting and unzipping of the DNA strand
Single strand acts as a template
Step 2 - Complementary base pairing by DNA polymerase
Adenine-thymine; cytosine-guanine
A-T
C-G
9
Q
what is DNA mutation
A
Any inherited alteration of genetic material
chromosome, aberrations
10
Q
Base pair substitution
A
One base pair is substituted for another
*not all genetic mutations especially base pair substitutions end up in an overt genetic abnormality, so much redundancy in the genetic code, duplications, backups,
11
Q
describe frameshift mutation
A
Insertion or deletion of one or more base pairs
Causes a change in the entire “reading frame”
12
Q
Spontaneous mutation
A
Mutation that occurs in absence of exposure to known mutagens, just happened
13
Q
Mutational hot spots
A
some part on some choromosomes that seem to mutate more than others, higher mutation rates
14
Q
what is a mutagen
give examples-
A
Agent known to increase the frequency of mutations
-radiation-exposure
-Chemicals
Nitrogen mustard, vinyl chloride, alkylating agents, formaldehyde, sodium nitrite
15
Q
describe what happens in transcription (it is mRNA synthesis)
-where does it move to?/ take place
-watch animation
A
RNA is synthesized from the DNA template
RNA polymerase binds to promoter site
Results in the formation of messenger RNA (mRNA)
RNA polymerase detaches
mRNA moves out of the nucleus and into the cytoplasm
Transcription continues until termination sequence is reached
WHERE mRNA is made*
unzips- the substances make base pairs
uses uracil
uses uracil
16
Q
explain gene splicing when does it occur?
A
Many RNA sequences are removed (introns), and those remaining are spliced together (exons) before mRNA migrates to the cytoplasm
-clean up of RNA sequences before the messenger RNA actually leaves the nucleus to the cytpoplasm
17
Q
Translation
describe the process?
site where it takes place?
what does it contain
A
Process by which RNA directs the synthesis of a polypeptide via interaction with tRNA
Site of protein synthesis is the ribosome
tRNA contains a sequence of nucleotides (anticodon) complementary to the triad of nucleotides on the mRNA strand (codon
In translation, messenger RNA (mRNA) is decoded by a ribosome, outside the nucleus, to produce a specific amino acid chain, or polypeptide.
The ribosome moves along the mRNA sequence to translate the amino acid sequence
Continues until termination sequence is reached
Then polypeptide is released into cytoplasm
18
Q
what is a somatic cells?
A
Contain 46 chromosomes (23 pairs)
Diploid cells
19
Q
Gametes (sperm and egg cells)
A
Contain 23 chromosomes
Haploid cells
One member of each chromosome pair
20
Q
meiosis
A
Formation of haploid cells from diploid cells
21
Q
mitosis
A
Formation of somatic cells
22
Q
explain autosomes and sex chromosomes
A
Autosomes
The first 22 of the 23 pairs of chromosomes in males and females
The two members are virtually identical and thus said to be homologous
Sex chromosomes
Remaining pair of chromosomes
In females, it is a homologous pair (XX)
In males, it is a nonhomologous pair (XY)
23
Q
what is a karyotype?
A
ordered display of chromosomes
24
Q
what is a euploid cell?
A
have a multiple of the normal number of chromosomes
Haploid and diploid cells are euploid forms
25
When a euploid cell has more than the diploid number, it is called
a polyploid cell
26
Triploidy/Tetraploidy
| survival rate?
Triploidy: a zygote having three copies of each chromosome (69 total)
Tetraploidy: four copies of each (92 total)
Neither triploid nor tetraploid fetuses survive
27
chromosome aberrations are?
| name the statistic
Leading cause of miscarriages and intellectual disability.
| 1 in 150 live births has a “major diagnosable chromosome abnormality” (Heuther 6th ed, p. 42)
28
what is aneuploidy? better to have..
A somatic cell (Contain 46 chromosomes (23 pairs) Diploid cells that does not contain a multiple of 23 chromosomes.
A cell containing three copies of one chromosome is trisomic (trisomy)
*extra than less*
29
what is monosomy
Monosomy is the presence of only one copy of any chromosome
| Monosomy is lethal, but infants can survive with trisomy of certain chromosomes
30
down syndrome (triploidy) has how many chromosomes?
47 (extra copy of 21 chromo.)
31
infants can't survive with monosomy but can with trisomy
Monosomy is lethal, but infants can survive with trisomy of certain chromosomes
32
what is a nondisjunction? chromo. abber. cont.
Usually the cause of aneuploidy
*three copies or 1 copy*
Failure of homologous chromosomes or sister chromatids to separate normally during meiosis or mitosis
33
partial trisomy
Only an extra portion of a chromosome is present in each cell
34
Chromosomal mosaics
Trisomies occurring only in some cells of the body
| -not every somatic cell is affected by the trisomy, only some cells in the body are affected
35
Down syndrome (Trisomy 21)
-stat of how many life births?
-physical features?
what is the risk age with mothers?
Best known example of aneuploidy
1:800 live births
Mentally challenged, low nasal bridge, epicanthal folds, protruding tongue, low-set ears, poor muscle tone
Risk increases with maternal age above 35
36
sex chromo. aneuploidy-
ex. trisomy X
what is one of the most common?
what are the symptoms?
One of the most common is trisomy X (a female who has three X chromosomes)
Symptoms are variable: sterility, menstrual irregularity, and/or intellectual disability
Symptoms worsen with each additional X
37
Sex Chromosome Aneuploidy (Turner syndrome)
what is it?
characteristics?
```
Females with only one X chromosome
Characteristics:
Underdeveloped ovaries (sterile)
Short stature (~ 4'7")
Webbing of the neck
Edema
Underdeveloped breasts; wide nipples
High number of aborted fetuses
X is usually inherited from mother
```
38
Klinefelter syndrome
Sex Chromosome Aneuploidy
give examples of genotype- when
what increases(X or Y? abnormalities?
```
Individuals with at least two Xs and one Y chromosome
Characteristics
Male appearance
Develop female-like breasts
Small testes—usually sterile
Sparse body hair
Long limbs
```
Some individuals can be XXY and XXXY
The abnormalities increase with each X
39
Abnormalities in Chromosome Structure
If a chromosome break does occur, physiologic mechanisms will usually repair the break
breaks can heal in a way that alters the structure of the chromosome
40
what are some reasons chromosomes break?
the repair isn't
Ionizing radiation, chemicals, and viruses
always perfect
41
Abnormalities in Chromosome Structure (Cont.)
what does deletions mean in this case?
describe cri du chat syndrome?
Breakage or loss of DNA (deletions)
```
Cri du chat syndrome
“Cry of the cat”
Deletion of
***short arm of chromosome 5***
Low birth weight, severe intellectual disability, and microcephaly (incomplete brain development)
```
42
Abnormalities in Chromosome Structure (Cont.)
Duplication
compare to deletion
what would happen in duplication in the same region as cri du chat?
Presence of a repeated gene or gene sequence
Less serious consequences because better to have more genetic material than less (deletion)
Duplication in the same region as cri du chat causes intellectual deficiencies but fewer physical abnormalities
43
Abnormalities in Chromosome Structure (Cont.)
INVERSIONS
how many breaks on the chromo?
when does it usually occur?
Two breaks on a chromosome
*means the code has slipped*
Reversal of the gene order
Usually occurs from a breakage that gets reversed during reattachment
ABCDEFG may become ABEDCFG
Position effect
44
Abnormalities in Chromosome Structure (Cont.)
Translocations (what is it?)
explain reciprocal vs. robertsonian?
The interchanging of material between nonhomologous chromosomes
Reciprocal translocation occurs when two chromosomes break and the segments are rejoined in an abnormal arrangement-genetic material gets exchanged
Robertsonian translocation occurs when fusion at centromere forms a single chromosome-two chromo break apart, begins differetly paired
45
Abnormalities in Chromosome Structure (Cont.)
Fragile Sites
most known example
Areas on chromosomes that develop distinctive breaks or gaps when cells are cultured
No apparent relationship to disease except for fragile X syndrome
46
Abnormalities in Chromosome Structure (Cont.)
Fragile X syndrome
which chromosome what arm?
what is it associated with?
higher incidence in males or females?
Site on the long arm of the X chromosome
Associated with intellectual disability; second in occurrence to Down syndrome
Higher incidence in males because they have only one X chromosome
47
genes- what is a locus?
Position of a gene along a chromosome
48
genes- what is a allele?
-what is polymorphism?
A different form of a particular gene at a given locus
Polymorphism
Locus that has two or more alleles that occur with appreciable frequency
49
you have 2 alleles at each
locus
50
Homozygous
Loci on a pair of chromosomes have identical genes (alleles)
51
Heterozygous
Loci on a pair of chromosomes have different genes (alleles)
52
Genotype (what they have)
The composition of genes at a given locus
53
Phenotype (what they demonstrate or exhibit)
The outward appearance of the genetics of an organism
54
genetics- An infant born with PKU genotype: if left untreated what happens? if treated?
intellectual disability becomes one aspect of the PKU phenotype
If treated, the child has an outwardly normal PKU phenotype.
55
genetics- carrier?
person who has a disease gene (genotype) but is phenotypically normal
they don't show the disease, they have it as a recessive trait
56
Transmission of genetic disease happens how?
Mode of inheritance
57
Mendel’s Laws of Inheritance
-describe mendel's two principles
Principle of segregation
-homo. genes separate during reproduction
Principle of independent assortment (mostly true) the transmission of one gene doesn't affect the transmission of another gene
58
Current understanding of chromosomal behavior is consistent..
with Mendel’s laws - chromosome theory of inheritance
59
“More than genetic traits and disease have been identified and catalogued” Huether 6th ed., p. 38
20,000
60
Pedigrees
-what is it?
Used to study specific genetic disorders within families
Begins with the proband, usually first person diagnosed
61
autosomal recessive
autosomal dominant
sex-linked recessive
sex-linked dominant
4 kinds of inheritance patterns
62
Single-Gene Disorders
Autosomal dominant inheritance
rarely causes?
when does it usual happen (more probability)
Relatively rarely causes diseases
Affected offspring usually produced by union of normal parent with affected heterozygous parent
Allele may be disease causing or normal
On average half of offspring will be normal, half will be heterozygous and express disease
when it is hetero-rare for both parents to have a dominant autosomal disease
63
Autosomal dominant inheritance
| / example / common to know if it's in the family
Example: Huntington disease
Neurological disorder, delayed age of onset
late 20's 30's
characterized by the progressive loss of brain and muscle function. Symptoms usually begin during middle age. The disease is inherited.
64
Single-Gene Disorders (Cont.)- what is the recurrence risk?
The probability that an individual will develop a genetic disease
65
Recurrence risk of an autosomal dominant trait
When one parent is affected by an autosomal dominant disease and the other is normal, the occurrence and recurrence risks for each child are one half
Must remember each birth is an independent event—EVERY child born, regardless of siblings’ outcome, has a recurrence risk of one half
-each new conception is a new roll of the genetic dice, not probability of another kid
66
Penetrance of a genetic trait
The percentage of individuals with a specific genotype who also express the expected phenotype
67
Incomplete penetrance
*find diagram*
Individual who has the gene for a disease but does not express the disease
-not a 100% of the genotype have the phenotype.
Retinoblastoma (eye tumor in children) demonstrates incomplete penetrance (90%)
68
Full (or nearly so) penetrance
Example: Autosomal dominant polycystic kidney disease (ADPKD)
Nephrons in kidney are replaced with cysts
Alterations in PKD1 or PDK2 gene
High recurrence risk
69
Expressivity
Extent of variation in phenotype (greater or lesser severity of the disease) associated with a particular genotype
This variation in gene expression can be caused by modifier genes, environmental factors, or different mutations at a locus
70
example of expressivity?
Hemophilia A caused by mutation that alters **one amino acid of the factor VIII gene is mild** , but a “stop” codon mutation leads to a more severe form, if there is another mutation, means it has worsen, not just at one location
-blood does not clot normally, bleeding in joints, bleeding anywhere,
71
Epigenetics – focus of Chapter 3
Same DNA sequence can produce different phenotypes due to chemical modification that alters expression of genes
-enviro. factors, what fetus is exposed to
72
Genomic imprinting
One parent imprints (inactivates) the gene during transmission to offspring- depending on the nature of the genes from the mother and father at a particular locus some gene activity is shut down
73
Autosomal recessive inheritance
- both parents are usually what?
- need two copies of the recessive gene to get disease?
-what is the recurrence risk for percent offspring chance?
In most cases, both parents of affected individuals are heterozygous carriers
Recurrence risk for offspring is 25%
Males and females equally affected
74
Autosomal recessive inheritance
- examples
- cystic fibrosis (carrier frequency)
-Autosomal recessive polycystic kidney disease (ARPKD) carrier frequency
have
Cystic fibrosis
Mutation in the cystic fibrosis transmembrane conductance regulator (CFTCR) gene
Carrier frequency is 1:29 whites in US
Autosomal recessive polycystic kidney disease (ARPKD)
People with ARPKD have inherited a faulty version of PDK1.
Cysts in kidneys develop much earlier than in people with ADPKD
Carrier frequency is 1:70 to 100
75
Consanguinity
increases autosomal recessive disease
Mating of two related individuals
Dramatically increases the recurrence risk of recessive disorders
State laws re: marriage of first cousins
76
Sex-Linked Inheritance
located where?
usually expressed by m/f? why?
Most sex-linked traits are located on the X chromosome and are said to be X-linked
Sex-linked (X-linked) disorders are usually expressed by males because females have another X chromosome to counteract the abnormal gene (heterozygous with a normal and abnormal gene at the locus)
77
Sex-Linked Inheritance (Cont.)
Duchenne muscular dystrophy
young men, kids, example of sex-linked
78
Sex-Linked Inheritance (Cont.)
X Inactivation
One X chromosome in females’ somatic cells is permanently inactivated early in embryonic development
Once X chromosome is inactivated in a cell; all descendants of that cell have the same chromosome inactivated
Random but fixed
Persons with abnormal numbers of X chromosomes may not follow the above pattern
Some regions on the X chromosome are not inactivated, so inactivation may be incomplete
79
Sex Determination
-where on the Y chromosome- from father
Sex determined by SRY gene on the short arm of the Y chromosome *the locus*
SRY- not only one location that affects your 2nd sex characteristics, triggers action of genes on other chromosomes
80
X-linked recessive
| Sex-Linked Inheritance (Cont.)
Most X-linked disorders are recessive
Affected males cannot transmit the genes to sons, but they can to all daughters
Sons of female carriers have a 50% risk of being affected
Additional example – hemophila A and hemophila B
can send bad x to daughters, then sons,
81
Sex-limited traits occur only in one sex- because?
of anatomic differences
Example
Inherited ovarian or testicular defects
82
Sex-influenced traits occur much more often in one sex than the other- examples
Examples
Male-pattern baldness – more common in males
Autosomal dominant breast cancer – more common in females
83
Mendel’s 2nd Law of Inheritance, Independent Assortment, is mostly true
occurs when?
Linkage of genes in the same region of a chromosome
Crossover
Occurs during meiosis I
Can cause recombinations of alleles located on the same chromosome
Frequency of recombinations used to map distance between loci on same chromosome
84
Gene mapping can identify links between a disease locus and a “marker” locus
Used to predict the probability of development of genetic disease
85
Polygenic trait
Variation in traits caused by the effects of several loci acting together
86
Multifactorial trait
Variation in traits caused by genetic and environmental factors
E.g., height, hypertension, diabetes mellitus
Have a threshold of liability – a certain number of defective alleles must be present to result in the disease/condition
87
Recurrence Risks
3 points
Recurrence risks of multifactorial diseases can change substantially between populations
Recurrence risk becomes higher if more than one family member is affected
Empirical risks have been derived via direct observation
88
Gene Therapy
explain how it works.
Experiments underway to treat genetic diseases
Replace a mutated gene with a healthy copy of the gene
Inactivate (“knock out”) a mutated gene
Introduce a new disease-fighting gene into the body
Replacement of mutated mitochrondrial DNA in the embryo from parents who delivered two previous children with Leigh Syndrome (news released in September 2016)
```
Adenosine deaminase (ADA) deficiency
Leber congenital amaurosis;
```
