Bio Final Exam Flashcards
(188 cards)
1
Q
Autosomes
A
Everything but sex chromosomes
2
Q
Sex Chromosomes
A
Sex-determining chromosomes. Represented as X and Y chromosomes for humans
3
Q
How many chromosomes do humans have, and how many are autosome or sex chromosome pairs?
A
22 pairs of autosomes and 1 pair of sex chromosomes, making the total number of chromosomes 46.
4
Q
What does 2n indicate about the number of chromosomes in a cell?
A
6 chromosomes in a cell. 3 from the mother and 3 from the father. n=3, so 2n = 6.
5
Q
Homologous chromosomes
A
a pair of chromosomes in a cell, where one chromosome is inherited from each parent.
6
Q
Sister chromatids
A
identical copies of a chromosome that are formed during DNA replication. The two sister chromatids form an x shape and are joined at the centromere.
7
Q
Meiosis
A
The reduction of chromosomes: multiple sets of each chromosome must be halved. This is necessary to avoid doubling the chromosome count each generation.
8
Q
What happens in the first and second rounds of meiosis?
A
First round: reduce from a diploid cell (two sets of chromosomes, 2n) to haploid cell (one set, n). This means the homologous chromosomes (chromosome pairs) are separated. Second round: divide from duplicated chromosomes (sister chromatids) to unduplicated chromosomes (individual chromatids)
9
Q
The results of meiosis
A
Results in 4 haploid cells with unduplicated chromosomes that are gametes (sperm or egg cells)
10
Q
The number of chromosomes and chromatids at the start and end of MITOSIS
A
Start (Before Division):
46 chromosomes
92 chromatids (each chromosome is duplicated)
End (After Division):
2 cells
Each with 46 chromosomes
Each chromosome has 1 chromatid → 46 chromatids
11
Q
The number of chromosomes and chromatids at the start and end of MEIOSIS I and II
A
Start (Before Division):
46 chromosomes
92 chromatids
After Meiosis I:
2 cells
Each with 23 chromosomes
Each chromosome still has 2 chromatids → 46 chromatids
After Meiosis II:
4 cells
Each with 23 chromosomes
Each chromosome has 1 chromatid → 23 chromatids per cell
12
Q
How many rounds of duplication does meiosis have compared to mitosis? Explain.
A
But meiosis includes two divisions (Meiosis I & II), but the DNA is only replicated once during interphase (S phase) — just like mitosis.
No second DNA replication happens before Meiosis II. This allows meiosis to produce 4 haploid cells with half the original number of chromosomes.
13
Q
Why is anaphase so important/unique in meiosis?
A
Chiasmata (crossing over points) are broken → homologous chromosomes separate.
BUT the sister chromatids stay together (they do not separate yet)!!
This ensures each new cell gets one chromosome from each pair, still in duplicated form.
14
Q
The product of meiosis 1 vs meiosis 2
A
Meiosis I:
2 haploid cells
Each with duplicated chromosomes (sister chromatids still attached)
Meiosis II:
4 haploid cells total (2 from each Meiosis I product)
Each with unduplicated chromosomes (sister chromatids have separated)
15
Q
Crossing over
A
An exchange of genetic material between chromosomes.
Two non-sister chromatids in two homologous chromosomes cross to form an x-shaped point of contact (the chiasmata) to exchange genetic material.
This causes sister chromatids to not be identical and leads to a ton of genetic variation that you don’t get from mitosis.
16
Q
What is the product of crossing over?
A
Recombinant chromosomes.
17
Q
Recombinant chromosomes
A
Chromosomes that have a mix of genetic material from both parents due to crossing over.
Normally, you inherit one chromosome of each pair from your mom and one from your dad.
During meiosis, matching chromosomes (one from each parent) line up and may exchange pieces of DNA with each other.
This swapping creates new combinations of genes, which is why these are called recombinant chromosomes.
It increases genetic diversity in offspring and is a key reason why siblings can look different even though they have the same parents.
18
Q
Meiosis I Prophase I
A
The first stage of meiosis I. First, the chromosomes condense. Next, homologous chromosomes pair up in a process called synapsis. Then, crossing over occurs which exchanges genetic material between chromosomes. Lastly, the nuclear envelope starts to break down and spindle fibers start to form.
19
Q
Chiasmata
A
the visible x-shaped points of contact between two non-sister chromatids in two homologous chromosomes that form for crossing over
20
Q
Tetrad
A
the group of 4 chromatids held together by the chiasmata.
21
Q
Major difference #1 between mitosis and meiosis 1
A
Crossing over occurs in meiosis (specifically meiosis 1). This leads to a ton of genetic variation that you don’t get from mitosis.
22
Q
Meiosis II is similar to mitosis in that the number of chromosomes remains intact throughout the process. Explain.
A
During meiosis 1, homologous chromosomes separate. During meiosis II, sister chromatids separate. Thus, between the two parts, the number of chromosomes stays the same
23
Q
What are the three ways to introduce genetic variation during sexual reproduction?
A
Independent assortment
Crossing over
Random fertilization
24
Q
Meiosis 1 - Prometaphase 1
A
First, the nuclear envelope fully breaks down. Then spindle fibers attach to chromosomes at their kinetochores. Then tetrads (paired homologous chromosomes) start moving toward the metaphase plate.
25
Meiosis 1 - Metaphase 1
First, tetrads line up along the metaphase plate. Then, spindle fibers attach to each homolog in the tetrad from opposite poles. The way the tetrads line up is random (independent assortment), which increases genetic variation. By the end, the cell is ready to separate the homologous chromosomes.
26
Independent Assortment
Each pair of homologous chromosomes randomly decides which chromosome (either from mom or dad) Each pair of homologous chromosomes randomly decides which chromosome (either from mom or dad) will go into each new cell, independently of what the other chromosome pairs are doing (thus the randomness).
Example: You have two sets of clothes: Mom's shirt + Mom's pants and Dad's shirt + Dad's pants. You get to put one shirt and one pair of pants in your suitcase, but you can randomly mix and match Mom's shirt with Dad's pants, Dad's shirt with Mom's pants, etc. In the same way, you have 2 chromosome pairs (like the 2 sets of shirts and pants) that can be randomly mixed and matched in the daughter cell, which will have only 2 chromosomes (1 chromosome from each pair) instead of 4 chromosomes (2 pairs).will go into each new cell, independently of what the other chromosome pairs are doing (thus the randomness).
27
Mitosis vs Meiosis 1 - Major difference #2
They differ in metaphase plate alignment.
Meiosis I: Tetrads (homologous chromosomes) align at the metaphase plate and are separated, reducing the chromosome number from 2n to n.
Mitosis: Sister chromatids align at the metaphase plate and are separated, maintaining the chromosome number (duplicated to unduplicated).
28
Meiosis 1 Anaphase 1
Homologous chromosomes are pulled apart to opposite poles of the cell. Each chromosome still consists of two sister chromatids.
The chiasmata (the point where chromosome pairs connect) are broken but sister chromatids remain attached at the centromere
29
Mitosis vs Meiosis 1 - Major difference #3
Mitosis: sister chromatids are separated
Meiosis I: Homologous chromosomes are separated but the sister chromatids stay together
(The sister chromatids are separated in Meiosis II)
30
Meiosis 1 telophase 1 and cytokinesis
During Telophase I: the separated chromosomes reach the opposite ends of the cell and the nuclear envelop reforms around them at each end
During Cytokinesis, the cell splits into two new cells, forming two haploid (n) daughter cells. Each new cell has half the chromosomes, but each chromosome still has 2 sister chromatids.
*Due to crossing over, the sister chromatids may not be identical which is another big difference from mitosis!
31
Synaptonemal complex
a protein structure that forms between homologous chromosomes during prophase of meiosis I to facilitate crossing over
32
Meiosis II
Meiosis II is essentially mitosis with haploid cells (the ones produced during meiosis I). However, in meiosis II, the sister chromatids are not genetically identical (due to crossing over) like they are in mitosis.
33
asexual reproduction produces what type of offspring?
genetically identical offspring, clones
34
Asexual reproduction
generation of offspring from a single individual. Offspring are genetically identical to the parent and siblings.
35
5 main methods of asexual reproduction
1. Budding
2. Binary fission
3. Cloning
4. Vegetative propagation
5. Parthenogenesis
36
Advantages and the one disadvantage of asexual reproduction:
Advantages:
The population can increase rapidly when the conditions are favorable
Only one parent is needed
It is more time and energy efficient as you don't need to find and maintain a mate
It is faster than sexual reproduction
Disadvantage: no variation whatsoever
37
Why is genetic variation important?
It ups the chance of survival in a changing world
38
Sexual reproduction is reproduction arising from...
the fusion of two gametes
39
The diploid-dominant life cycle
Type of life cycle where the dominant stage of an organism's life is diploid (having two sets of chromosomes, one from each parent).
Meiosis produces haploid gametes, which fuse during fertilization to form a diploid zygote that grows into the adult organism.
40
The two other types of life cycles besides the diploid dominant life cycle
the multicellular haploid cycle and the alternating multicellular haploid and diploid cycle.
41
What are gametes and are they genetically identical?
They are sex cells, haploid (n) cells. Not identical.
42
How are gametes produced?
Via meiosis carried out by the gonads (reproductive glands, the testes in males and the ovaries in females).
43
During fertilization, what do the two haploid cells form?
A diploid zygote (a diploid fertilized egg cell resulting from the union of the sperm and egg). Sperm (n=23) + egg (n=23) = zygote 2n = 46
44
In species that sexually reproduce, the behavior of ____ during ____ is responsible for most of the variation that arises each generation.
chromosomes during meiosis and fertilization
45
Random Fertilization
Any sperm can fertilize any egg, regardless of which sperm or egg it is.
The total possible number of different gametes is 2^n
Sperm + egg will yield 70 trillion combinations (2^23)^2
2^n = the number of genetically different gametes an individual can produce (n = number of chromosome pairs).
In humans, n = 23, so each person can make 2²³ ≈ 8.4 million different gametes.
When any sperm (2²³) meets any egg (2²³) → (2²³ × 2²³) = 70 trillion possible zygote combinations.
46
Spermatogenesis
generation of sperm cells
47
Oogenesis
generation of egg cells
48
mitosis vs meiosis (DISCOPUG)
Mitosis listed first, then meiosis.
Divisions: one, two
Independent Assortment: no, yes (metaphase I)
Synapsis: no, yes (form bivalents)
Crossing Over: no, yes (prophase I)
Outcome: two cells, four cells
Ploidy: diploid, haploid
Use: body cells, sex cells (gametes)
Genetics: identical cells, variation
49
Homozygous
An organism has two identical alleles for a trait (e.g., AA or aa).
50
Heterozygous
An organism has two different alleles for a trait (e.g., Aa).
51
What are the two main things Gregor Mendel is known for?
1. Used garden peas to document a mechanism of inheritance called complete dominance
2. Identified two fundamental laws of inheritance: independent assortment and segregation
52
How did Mendel control the mating of pea plants?
Normally they self-fertilize but he manually cross-pollinated them. HE ONLY CONTROLLED THE P GENERATION
53
P1 generation
(parental generation) consists of two true-breeding plants with contrasting traits, such as purple flowers and white flowers.
54
F1 generation
(first filial generation) is the offspring of the P1 cross, and all showed only one of the parental traits (e.g., all had purple flowers), demonstrating dominance.
55
Character
a heritable feature (like flower color). Similar to phenotype (physical appearance)
56
Trait
a variant of a character (like a purple or white flower)
57
Locus/Loci
a specific location on a chromosome where a gene is located
58
Alleles
Alternative versions of the same gene (blue eyes vs brown eyes). Represented by capital and lowercase letters in Punnet squares
59
Genotype
The genetic makeup of an organism (PP, Pp, or pp) (these can be any letters but the important part is that they represent alleles with the capital being dominant and the lowercase being recessive)
60
Phenotype
The physical, observable features or traits of an organism, which are primarily determined by its genotype, but can also be influenced by the environment.
61
True-breeding organisms
Pure-bred organisms. Organisms that always pass down a specific phenotypic trait. White flower + white flower = white flower (always)
62
F2 generation of truebred parents: cross of Rr x Rr from the F1 generation:
Results in a 3:1 phenotype ratio of dominant to recessive (75% dominant), revealing that the recessive trait is still present and inherited. Draw a punnet square to help you see
63
Mendel's 1st Law: The Law of Segregation
Every individual has two alleles for each gene, but only one allele is passed on to each gamete. Meaning, the two alleles separate (segregate) during the formation of gametes in meiosis.
64
For each characteristic, an organism inherits...
two alleles, one from mom, one from dad.
65
If the two alleles that the organism inherits (if the two alleles at the locus) are different, which one will determine the organism's appearance (phenotype)?
The dominant allele
66
Hybridization
Crossing two true breed plants (RR x rr). Always results in a F1 (1st filial) hybrid generation of 100% heterozygotes (Rr). Draw it out on a Punnet square so you can see the heterozygotes
67
What can we assume about the parental generation of mendelian genetics?
It is always true breeding
68
Dihybrid cross
A genetic cross that examines the inheritance of two different traits at the same time.
It involves individuals that are heterozygous for both traits (e.g., AaBb × AaBb).
A Punnett square for a dihybrid cross is a 4x4 grid.
The classic phenotypic ratio (if both traits follow simple dominance) is 9:3:3:1
69
What gametes are possible if the parent has the gene AaBb?
FOIL method (like in algebra) yields:
AB, Ab, aB, and ab.
70
Mendel’s 2nd Law: Independent Assortment
Alleles of unlinked genes assort independently and are randomly distributed into gametes
Alleles from 1 gene do NOT affect which alleles from another gene a gamete will receive
Mendel identified his 2nd law of inheritance by following 2 characteristics simultaneously
Pea color & pea pod texture
Accomplished this by crossing two parents that were true-breeding for BOTH characteristics
71
Multiplication Rule
The probability that 2 or more independent events will occur together is the product (multiplication) of their individual probabilities.
The probability of (A and B) is the probability of A times the probability of B.
Example:
The chance of rolling a 5 on a die is 1/6
The chance of rolling a 4 on a die is 1/6
So, the overall chance of rolling exactly a 5 on the first die and then a 4 on the second die is: 1/6 X 1/6 = 1/36
72
Addition Rule
The probability that any 1 of 2 mutually exclusive events will occur is calculated by adding together their individual probabilities.
For Example:
If one can win by rolling a 4 or 5 with one die, then the overall chance is:
The chance of rolling a 4 is 1/6
OR the chance of rolling a 5 is also 1/6
So, the overall chance of winning is: 1/6 + 1/6 = 2/6 = 1/3
73
Codominance
2 dominant alleles affect the phenotype in separate, but distinguishable, ways
When two alleles express separate and equal phenotypic traits
The heterozygous individual expresses both traits
74
Codominance examples:
Camelia flower - both red and white petals
Blood type AB: both the A and B antigens are present
75
Incomplete Dominance
The phenotypes of F1 hybrids is somewhere between the phenotypes of the 2 parental varieties. (ex: white flower + red flower make pink flower)
76
incomplete dominance example
pink snapdragon (white snapdragon + red snapdragon make pink snapdragon)
77
Complete Dominance (AKA Mendelian Inheritance)
Occurs when the heterozygote (Rr) and the homozygous dominant (RR) have the same phenotype.
Just one dominant allele is enough to show the full trait.
Example: PP = purple, Pp = purple (pea flowers)
78
What does "multiple alleles" refer to and what are some examples?
Multiple alleles is when more than two alleles exist for a trait. In simple mendelian genetics, there is usually just one dominant and one recessive allele per trait.
But sometimes there are more than two options: the trait for hair color in rabbits has 4 allele options, and human blood types have 3 options (A, B, and O which can combine in different ways).
79
Lethal alleles
Can be dominant or recessive, cause death when present.
"Lethal" doesn't always mean immediate death -- just means life expectancy is significantly shortened
80
3 diseases caused by lethal alleles
Tay-Sachs, Huntington's, and Cystic Fibrosis
81
Huntington's Disease
Requires the dominant allele H, so if you have the genotype HH or Hh you will get the disease.
However, symptoms may not occur until age 40, at which point the afflicted person has prob already passed the allele to 50% of their offspring oop--
82
Manx cat genetics
Manx cats have no tails, caused by the special dominant allele M^L.
The normal cat tail allele is M.
If a cat has the genotype MM, they'll be a normal cat. If its M^LM, they'll be a manx cat. If they get M^LM^L (so two copies of the manx allele), this is LETHAL and the cat will die before birth.
Most heterozygote crosses yield a 3:1 dominant phenotype ratio, but on the punnet square since one of the genotypes will be M^LM^L, this cat will die so the ratio will be 2:1 dominant manx allele instead.
83
One mutant allele can be dominant over all other phenotypes, including the wild type. Give an example
A good example is Antennapedia in fruit flies (Drosophila).
In flies with the Antennapedia mutation, they grow legs on their heads instead of antennae.
This mutation is dominant, which means just one copy of the mutant gene is enough to cause the change (even if the other copy is normal).
The mutation changes where the gene is active, so it mistakenly causes leg development in the head.
84
Pleiotropy
Pleio means many, tropy means change
A gene has multiple (seeming unrelated) phenotypic effects
An allele causes multiple characteristics.
Example: Sickle-Cell Anemia
The mutation of a single genes leads to sickle cell anemia, which is a debilitating disease affecting the shape of red blood cells
This one mutated gene can also cause:
Blindness
Heart Failure and/or cardiac arrest
Liver and other organ failure
85
Polygenic Traits
Poly means many, genic means gene
exact opposite of pleiotropy)
Some characteristics/traits may be determined by 2 or more genes (100s – 1000s even)
86
Epistasis
a gene at 1 locus alters the phenotypic expression of a gene at another locus
Phenomenon where the effect of a gene depends on the presence or absence of one or more other genes (called gene modifiers)
Presence or absence of one gene affects the phenotype of another gene
87
Quantitative Inheritance
A type of polygenic inheritance where a trait is controlled by many genes (polygenes), each contributing a small, additive effect. This results in a large range of possible phenotypes, not just one or two.
Human height is a PERFECT example. There’s no dominant or recessive "height gene" — instead, the effects of many alleles add up.
88
The chromosome theory of inheritance
Mendelian genes have specific loci on chromosomes
Chromosomes undergo segregation & independent assortment
89
What did Thomas Hunt Morgan provide convincing evidence for?
Evidence that chromosomes are the location of Mendel’s heritable factors (genes)
90
What did Thomas Hunt Morgan first observe and note, and what did he determine from this?
He observed wild type (wt): “normal” common phenotypes in the fly populations, and mutant phenotypes: traits alternative to the wild type
Morgan determined that the white eye mutant allele must be located on the X chromosome
He concluded that all F1 offspring had red eyes, so the mutant white-eye trait (w) must be recessive to the wt red-eye trait (w+)
Since the recessive trait was expressed only in males in the F2 generation, the eye-color gene must be located on the X chromosome
Meaning that there is no corresponding locus on the Y chromosome
91
Why do we care about Morgan's research?
Was the first solid evidence indicating that a specific gene is associated with a specific chromosome
Earned him the Nobel Prize in Physiology or Medicine in 1933
92
Mendel's experiments with pea plants showed that the purple flowers were _________ over the white flowers.
completely dominant
93
In a cross between AaBbCc x AaBBCC, what is the probability that the offspring will be AaBbCC?
Rule of multiplication
1/2x1/2x1/2=1/8
94
In the Camelia flower, the same flower has both red and white petals. This is an example of ________________.
codominance
95
Epistasis is a type of which type of inheritance pattern?
polygenetic traits
96
The works of Thomas Hunt Morgan on Drosophila showed that the genes for eye-color must be present on which chromosome?
the x chromosome
97
Theodor Boveri
observed that proper sea urchin embryonic development does not occur unless chromosomes are present
98
Walter Sutton
observed chromosome separation in daughter cells during meiosis
99
Chromosomal Theory of Inheritance and who discovered it
identified chromosomes as the genetic material responsible for Mendelian inheritance. Proposed by Walter Sutton and Theodor Boveri
100
Did Mendel's work come before or after Boveri and Sutton's chromosomal theory?
After, because the theory identified chromosomes as the genetic material responsible for Mendelian inheritance.
101
Thomas Morgan observed that linked genes tend to...
Also what law does this observation violate?
Be inherited together and are physically located near each other on the same chromosome.
This violates the Law of Independent Assortment (which states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.)
102
Morgan's work with sex-linked traits showed that the trait for sex and the trait for eye color were __________ instead of ________ which is what you would expect from Mendel's second law (the law of independent assortment)
Inherited together instead of segregating independently
103
phenotype vs genotype
Genotype: an organism's genetic information. AKA BB, Bb, bb, bB.
Phenotype: an organism's set of observable physical traits from the genotype: AKA blue eyes, brown eyes.
104
Inheritance pattern of unlinked genes
* Unlinked genes are Independently assorted.
* 50% parental type offspring and 50% recombinant offsprings
* 1:1:1:1 ratio of phenotypes
105
Example of a homozygous dominant genotype
AA
106
Example of a heterozygous genotype
Aa
107
Example of a homozygous recessive genotype
aa
108
Linked genes are located _____ on the same chromosome and tend to be inherited ______.
close together, together
109
Linked genes display different _______ compared to unlinked genes.
offspring ratios
110
Inheritance patterns of linked genes
* linked genes are NOT independently assorted.
* No recombinant offsprings, all are parental type
* 1:1:0:0 ratio of phenotypes
111
What happens if crossover
always occurs between
homologous chromosomes?
1:1:1:1 ratio of phenotypes
* 50% parental type offspring and 50% recombinant offsprings
* linked genes ACT LIKE independently assorted.
112
Based on Morgan's results, the actual frequency of getting recombinant offspring is...
between 0%-50%
113
What factor determined the recombination frequency?
The greater the distance between two genes on a chromosome, the more points there are between them where crossing over can occur.
114
Recombination frequency
the frequency with which a single chromosomal crossover will take place between two genes during meiosis.
Ex: (391 recombinants/2,300 total offspring) x100 = 17% recombination frequency
115
Recombination frequencies can be used to map the relative position of ______. This is called a ________.
genes on chromosomes. Linkage map
116
The centimorgan
gmu, genetic map unit, AKA the Centimorgan in honor of TH Morgan. This unit is equal to 1% recombination
117
Karyotype
A full image of an organism's entire chromosome collection. For humans there are 23 pairs of chromosomes.
118
What is the exception to the order of chromosomes in the human karyotype?
They're supposed to be numbered largest to smallest but chromosome 21 is actually smaller than 22. But it's kept like that for historical reasons
119
Nondisjunction
results when a cell has an abnormal chromosome number (common in plants)
120
Aneuploidy
A condition in which the offspring have an abnormal number of a particular chromosome
121
Polyploidy
occurs when there are more than 2 complete sets of chromosomes in an organism. Very common in salmon, carp, bananas, wheat, and strawberries
122
Euploidy
the normal number of chromosomes in a gamete. Eu = true and ploidy = number of
123
Why are female mammals mosaics for X-linked traits? What does this mean?
Females have 2 X chromosomes; males have only 1.
During development, 1 X in each cell is randomly inactivated (X-inactivation).
This is controlled by XIST (X-inactive specific transcript).
If a female is heterozygous for a gene on the X, different cells may express different alleles.
This creates a mosaic pattern of gene expression.
Example: Only female cats can have tortoiseshell coat color because it requires two different X-linked coat color alleles.
124
Trisomy 21 (Down Syndrome)
Most common genetic birth defect
Characteristic facial and limb features
* Increased risk of leukemia
* Issues with immune, GI, and nervous systems
* Generally, very social and outgoing
125
Triple-X Syndrome
Female (XXX)
* 1 in 1000 births, up to 90% undiagnosed as
symptoms are not usually “extreme”
* Usually mild due to Barr bodies (X “silencing”)
* Stable hormone treatment can improve symptoms,
but there is no cure
126
Turner's Syndrome
Female (X), often infertile
* 1 in 2500 births, much more severe than XXX
* Significant issues related to heart and kidneys
* Growth hormones and estrogen therapy can be used to
help treat symptoms, but the condition is permanent
127
Klinefelter's Syndrome
Male (XXY), usually infertile
* Most common cause of hypogonadism, a condition that
stops the body from producing sperm and testosterone
* As many as 75% of men will go undiagnosed, usually
seeking medical attention after issues with fertility or loss
of sex drive
* Can be treated (not cured) with testosterone therapy
128
Jacob's Syndrome
Male (XYY), 1 in 1000 males affected
* Many men will go undiagnosed due to usual “mild”
symptoms
* Can be diagnosed along with autism
129
Cri-du-chat syndrome
Chromosome deletion.
A human genetic disorder resulting from a chromosomal recombination mutation that causes a deletion of a portion of chromosome 5 (5p = petite
arm). * Infants with this genotype emit a characteristic high- pitched cry on which the disorder’s name is based
130
Genetic mutation
any change in a DNA sequence
131
Genetic mutations can be ______ or can be ________ by _________.
spontaneous, induced by mutagens
132
The four types of mutations with examples:
Substitution, insertion, deletion, and inversion
examples:
Normal: BEAST
Substitution: FEAST (substitutes one letter for another)
Insertion: BREAST (inserts an extra letter)
Deletion: BEST (deletes a letter)
Inversion: BEATS (inverts/reverses the position of two of the letters)
133
Point mutations
the change of a single nucleotide in the template DNA
134
What is the point mutation that causes sickle cell disease?
Normal hemoglobin becomes sickle cell (mutant) hemoglobin when the glutamic acid (Glu) becomes valine (Val).
Remember that valine and glutamic acid are amino acids and each one is coded by a codon (a sequence of three nucleotides). Just changing one nucleotide will change the codon, which changes the amino acid
135
The two categories of point mutations
Indels (base-pair INsertions or DELetions) or substitutions (base-pair substitutions)
136
Silent (synonymous) substitutions
- Change in a nucleotide WITHOUT changing an amino acid
- Results from redundancy in amino acid chart
- Allows for maintenance of gene with variation to genome
137
Missense (nonsynonymous) substitutions
Change in a nucleotide that results in a change to the amino acid
138
Nonsense substitutions
- Mutations that cause the encoding of a premature stop codon, causing transcription and translation to stop
- Usually causes loss of function, but can cause new function in some cases
139
Frameshift mutations
when the reading frame shifts by one nucleotide and completely messes everything up
140
What causes frameshift mutations?
indels (insertion or deletion).
Example:
Normal: SEE THE DOG RUN
Insertion: SEE ETH EDO GRU N
Deletion: SET HED OGR UN
141
How many nucleotides in indel mutations will NOT cause a shift in the reading frame but will lead to an insertion or deletion of an amino acid in the protein?
3 (because one amino acid is coded for by 3 nucleotides)
142
The control of which genes are expressed dictates...
whether a cell is a muscle, nerve, or liver cell
143
It is the differential gene expression patterns that arise in different cells that...
give rise to a complete organism
144
What three things does gene regulation determine?
1. What cell type each cell will differentiate into
2. Patterns and paths of gene expression during embryo development
3. Gene expression patterns in mature (differentiated) cells
145
Cell differentiation
the process unspecialized cells go through that develops them into specialized cells with distinct structures and functions
146
In what three ways does gene regulation maintain efficiency?
1. Energy - expressing all genes would require a massive amount of energy
2. Space - cells are kept to a manageable size
3. Time - Genes can be expressed as needed and more rapidly
147
In prokaryotes, transcription and translation occur ______ in the __________. Therefore, gene regulation is restricted to a ________ level.
simultaneously in the cytoplasm, transcriptional level
148
Operons
Prokaryotes organize their genes into sections within their genome called operons: they are independent genes coding for independent enzymes that are somewhat functionally related in the cell
149
What 3 types of regulatory molecules are operons controlled by?
1. Repressors - suppress transcription and gene expression
2. Activators - enhance transcription and gene expression
3. Inducers - suppress or enhance transcription and gene expression depending on current needs of each cell
150
Two major examples of operons:
Trp (tryptophan) operon and Lac operons
151
Trp operon
Tryptophan operon. Known as a repressible operon: it is regulated by a repressor. If tryptophan is plentiful in the cell's environment, then the operon is turned off. If tryptophan is low and the cell needs to make it, the operon is on.
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Lac operon
Known as an inducible operon: it is regulated by inducers that can either activate or repress transcription. Specifically, it is regulated by the inducers allolactose and catabolite activator protein (CAP)
153
What conditions will ensure optimal transcription of the lac operon/expression of beta gal?
no glucose, high lactose
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Eukaryotic Regulation of Gene Expression
Transcription and RNA processing occur in the nucleus. Translation and post-translational modification occur mostly in the cytoplasm.
1. epigenetic level
2. transcriptional level
3. post-transcriptional level
4. translational level
5. post-translational level
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Which level of eukaryotic regulation of gene expression does NOT occur in the nucleus?
The translational stage
156
In post-transcriptional regulation of gene expression, where are the untranslated regions of mRNA (UTRs) found on the mature mRNA?
At both the 5' and 3' ends
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Epigenetic Regulation
regulation controlling the frequency, rate, or extent of gene expression in a way that is inheritable but does not change the DNA sequence
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Transcription Level Regulation
Initiation of transcription is one of the key stages to regulate gene expression! This is achieved through the regulation of RNA polymerase recruitment. RNA polymerase requires transcription factors (TFs) to initiate transcription
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Transcription Factors
Proteins that control binding and initiation of transcription. Can function as regulators in the form of repressors and activators. Bind to promoter sequences and regulatory sequences.
160
Promoters
Specific sequences upstream of the gene sequence that bind TF. Different genes may have the same promoter
161
TATA box
a string of T and A nucleotides in a eukaryotic promoter that is used by TF for binding and recognition
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Proximal CE (control elements)
Regulatory sequences of DNA that are found close to promoters of the genes they help to regulate. (Within 200 base pairs). Bind specific activator or repressor proteins to affect the rate of transcription
163
Distal CE (control elements)
Found FAR from the genes they help to regulate.
Enhancers: short regulatory sequence that promotes transcription by binding to activator proteins.
Silencers: short regulatory sequence that decreases transcription by binding to repressor proteins.
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Post-transcriptional regulation
Untranslated regions of mRNA (UTRs)
Found on both the 5’ and the 3’ ends of the mature mRNA.
The provide binding sites for specific proteins that influence RNA stability (increasing or decreasing)
microRNAs (miRNAs)
Short RNA molecules (21-24 nucleotides) that recognize a specific sequence on mature mRNA.
Interact with a special protein complex called RNA-inducing silencing complex (RISC)
miRNA/RISC complex binds & degrades targeted mRNA
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Translational Level Regulation
Translation is regulated and controlled by proteins that bind and initiate the start of this process
This results in the formation of the initiation complex
Eukaryotic initiation factor-2 (eIF-2)
This is the 1st protein to bind the small subunit of the ribosome and form the complex
Methionine initiator tRNA binds mRNA and binds the above complex
Phosphate and eIF-2 are released and the large ribosomal subunit binds
Translation occurs
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Post-translational regulation
Proteins can be chemically modified (added or removed)
These chemical changes regulate protein activity or the length of time they exist in cell.
For example, proteins with ubiquitin tags are marked for degredation
167
Cancer results from genetic changes that affect __________
cell cycle control
168
The gene regulation systems that go wrong during cancer are the same systems that play important roles in:
Embryonic development, the cell cycle, DNA repair
169
The three types of genes associated with cancer
Proto-oncogenes, oncogenes, and tumor-suppressor genes
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Proto-oncogenes
Normal cellular genes that code for proteins that control normal cell growth and division
Positive cell-cycle regulators
171
Oncogenes
Abnormal cancer-causing versions of proto-oncogenes (mutations)
Alter transcriptional activity of a gene that controls cell growth
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Tumor-suppressor genes
Encode proteins that inhibit abnormal cell division
Function to prevent excessive or inappropriate cell growth
Negative cell-cycle regulators
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Three additional cancer contributors:
1. inheritance and predisposition (Individuals who inherit a mutant oncogene or tumor-suppressor allele have an increased risk of developing certain types of cancer)
2. mutagens (Carcinogens can cause damage and mutations to your DNA)
3. certain viruses (These viruses promote cancer by integrating their own DNA into a cell’s genome)
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Human Papillomavirus (HPV)
The most common STD with more than 80 million Americans affected
14 million new cases yearly
It usually goes away on its own but can cause genital warts
99% of cervical cancer is attributed to past HPV
NINETY-NINE PERCENT
However, it’s nearly 100% preventable because of a vaccine
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Who gets cancer?
"Twelve thousand kids per year get cancer in the US. But the extraordinary thing isn't that cancer happens. The extraordinary thing is that cancer doesn't happen more often. Every human life begins with a single cell."
176
Circadian clocks
Internal clock that is roughly a 24 hour cycle in the processes of ALL organisms (plants, animals, fungi and cyanobacteria)
Circadian rhythms are endogenously generated, although they can be affected by external cues such as sunlight and temperature
Circadian rhythms are important in determining the sleeping and feeding patterns of all animals, including us
Clear patterns of brain wave activity, hormone production, cell regeneration, and other biological activities linked to this daily cycle
177
In studying the role of gene expression regulation in cancer development, under normal conditions, the Ras gene is a ___________, whereas p53 is a type of __________.
proto-oncogene, tumor suppressor gene
178
Tortoiseshell coat color is seen in female cats due to the one of the two copies of a certain chromosome being inactivated. Which chromosome is this?
The X chromosome
179
Which phase of meiosis can also be called the reductional phase and involves the reduction of chromosome number from 2n to n?
Meiosis I
180
When glucose concentration is plentiful in a cell, for lac operon, _____ concentration will be low and ___________ complex will not bind to the CAP site.
cAMP, CAP-cAMP
181
In eukaryotic translation level regulation, the ___ binds to the small ribosomal subunit (40S). The phosphorylation of this protein blocks translation initiation of...
eukaryotic initiation factor 2
182
When studying inheritance patterns of unlinked genes, what percent of the offspring would be recombinant if the genes observed are on different chromosomes and are independently assorted?
50%
183
In post-transcriptional regulation of gene expression in eukaryotes, Un-Translated Regions (UTRs) are present on both the 3' and 5' ends of the mRNA and can influence _________.
RNA stability
184
Starting with one diploid cell, mitosis results in the production of ______ daughter cells, whereas meiosis results in the production of _______ daughter cells.
two diploid, four haploid
185
The coat color in labradors is an example of varying dominance type. The effect of the gene on the B locus is determined by the type of allele on the ____________.
E locus.
186
Which phase of meiosis can result in the formation of recombinant chromosomes from crossing over?
Prophase I
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wild type gene
The most common or "normal" version of a gene.
It’s considered the standard or reference against which mutations (non-wild types) are compared.
Example:
In fruit flies, the wild-type eye color is red.
A mutation might result in white eyes, which is a mutant phenotype.
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6 main syndromes resulting from chromosome changes, and what those changes are:
Down Syndrome (Trisomy 21): extra copy of chromosome 21
Triple-X Syndrome: Female XXX
Turner's Syndrome: Female X
Jacob's Syndrome: Male XXY
Klinefelter's Syndrome: XYY
Cri-Du-Chat Syndrome: deletes the petite (p) arm of chromosome 5
