Weeks 1-3 Flashcards
Midterm 1 (110 cards)
1
Q
natural selection
A
individuals with certain traits are more likely to survive and reproduce in a given environment
2
Q
artificial selection
A
humans choose what reproduces
3
Q
gregor mendel did his experiments with what?
A
garden peas
4
Q
phenotype
A
- an individuals observable characteristics
- largely determined by genotype
- commonly referred to as a trait
5
Q
pure breeding
A
parents are homozygous for certain traits
6
Q
genotype
A
- genetic makeup
- description of the genetic information carried by an individual
7
Q
gene
A
discrete units of inheritance
- sequence of DNA
- appears the same on a chromosome
– can have 2 copies of a gene but they may not be the same
8
Q
allele
A
alternative forms of a single gene
9
Q
homozygous
A
two of the same allele for a given gene
10
Q
heterozygous
A
two different alleles for a given gene
11
Q
in every population there will always be different versions (alleles) of every gene. why?
A
mutation
12
Q
polymorphic
A
more then one normally occurring allele in the population
13
Q
a maximum of two alleles for one gene can exist in a ______ individual
A
diploid
- only 2 alleles for a given gene, one from each parent
14
Q
monomorphic
A
genes that have only one allele that is normally present in the population (in nature)
- ex: rabbits
15
Q
Mendel’s law of segregation
A
the two alleles (in a diploid organism) for each trait separate (segregate) during gamete formation, then unite at random, one from each parent, at fertilization
16
Q
a monohybrid cross using pure-breeding plants will have what in the first generation and what in the second generation?
A
F1- all dominant trait
F2- 3:1 ratio dominant: recessive
17
Q
test cross
A
cross the individual with unknown genotype against a homozygous recessive phenotype for the trait in question
18
Q
law of independent assortment
A
describes how different alleles of different genes behave
19
Q
the law of product
A
the probability of two or more independent events occurring together is the product of the probabilities that each event will occur by itself
ex: chance of flipping heads twice in a row
- 1/2 x 1/2 = 1/4
20
Q
the law of sum
A
the probability of either of two mutually exclusive events occurring is the sum of their individual probabilities
ex: chance of rolling an even number on a six sided dice
- 1/6 + 1/6 + 1/6= 3/6= 1/2
21
Q
incomplete dominance
A
the heterozygote has an intermediate phenotype
- combination of the two parents
- ex: red + white = pink
geno: 1:2:1
pheno: 1:2:1
22
Q
complete dominance
A
normal cross breeding with one gene being dominant and one being recessive
geno: 1:2:1
pheno: 3:1
23
Q
codominance
A
contributions from both alleles are visible (distinctly from each other, not as an intermediate) in the phenotype
- both present at same time
ex: red + white = 1 red and white
geno: 1:2:1
pheno 1:2:1
24
Q
Wild type
A
the allele associated with the most common phenotype in a population
25
mutant type
rare alleles (opposite of wild)
- designated with superscript +
26
what about wild types and polymorphic genes?
more then one can be considered wild type - "common variants"
27
**Pleiotropy**
one gene influences multiple traits
ex: sickle cell disease
28
**Lethal alleles**
some dominant and recessive alleles can kill the organism
-- lethal allele's are generally pleiotropic
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Recessive lethal alleles
ex: yellow mice
grey mice carry AA, yellow are AyA
- 1:1 ratio of yellow and grey mice
two AyA breed:
AyAy is lethal
- pheno & geno ratio: 2:1
30
what happens if an allele is dominant for lethality?
- if it is lethal before birth or early childhood it can't be passed on
- can have lethal dominant alleles if they don't present until later, like Huntington disease
- could also be a new mutation
31
**Additive genes**
two or more genes influence one trait in a cumulative manner
ex: additive interaction between two genes producing lentil seed colour
- in a dihybrid cross of pure breeding tan and grey lentils all F1 seeds are brown
- F2 ratio: 9:3:3:1
brown:tan:grey:green
32
**Epistasis**
one gene hides the effect of another gene
- results from the effects of an allele at one gene masking the effects of another gene
- the allele that does the masking is *epistatic* to the other gene
- the gene that is masked is *hypostatic* to the epistatic allele
33
Is epistasis recessive or dominant?
r- epistatic allele must be homozygous for the effect of the hypostatic gene to be masked
d- one copy of an allele is sufficient to mask the hypostatic gene
34
Dominant epistasis (example)
example: summer squash
- fruit colour in summer squash is influenced by two genes
- gene A:
A___ = yellow
aa= green
- gene B:
B___ = white, regardless of gene A
bb= yellow or green, depending on gene A
phenotypic ratio: 12:3:1
genotypic: 9:3:3:1, but 9+3 are both white
35
recessive epistasis (example)
example: coat colour in Labradors
- controlled by two genes
B gene
- B___= black
- bb = chocolate
BUT only if there is a dominant E
ee masks the effects of the B gene and makes yellow labs
- ee is epistatic to any allelic combination of the hypostatic gene B
- phenotypic ratio: 9:3:4
- genotypic: 9:3:3:1 (3+1 are yellow)
36
**Complementary gene action**
two or more genes can work in tandem, in the same biochemical pathway, to produce a particular trait
37
Complementary gene action (example)
- Heterogenous trait
- a mutation in any one of a number of genes can give rise to the same phenotype
-- ex: mutation in the A gene (a allele) and B gene (b allele) both lead to the loss of colour (white)
-- mutation in either of the 2 will make the same mutation
-- at least one functional dominant A and B allele are needed for purple colour
--- needs an A and a B
phenotypic ratio: 9:7 (purple: white)
flower colour is a heterogenous trait with complementary gene action
38
Complementation test
observing if parents with the same mutant phenotype can produce offspring with restored function
39
Complementation test (example)
two deaf parents produce a hearing offspring
- shows the mutations in the two parents were in different genes
40
Complex traits/multifactorial inheritance
a trait is determined by many genes or by the interaction between genes and the environment
41
the same genotype does not always result in the same phenotype...why?
phenotype can be influenced by the environment, modifier genes and chance
42
**Penetrance**
percentage of the population with a particular genotype, that demonstrate the expected trait
43
**Expressivity**
degree or intensity with which a particular genotype is expressed in a phenotype within a population
44
Example of how individuals with the same genotype can have different phenotypes
All green
- complete penetrance an unvarying expressivity
Some green/Some white
- incomplete penetrance and unvarying expressivity
- only some individuals show the phenotype
Green/light green/dark green
- complete penetrance and variable expressivity
- everyone has it but at varying levels
White/dark green/green/light green
- incomplete penetrance and variable expressivity
- mix of both
45
**Sex-linked traits**
controlled by genes on the X or Y chromosome
- colour blindness
***other genes have different effects in males and females but are not carried on the sex chromosomes
46
**Sex-limited traits**
affect a structure or process found in only one sex
- horns in males or milk in females
47
**Sex-influenced traits**
show up in both sexes but their expression may differ between the sexes
- patterned baldness
48
The environment can also influence phenotype!
examples?
temperature, light, altitude can affect the phenotypic expression of a genotype
49
Example of environmental influence
Himalayan coat pattern in cats and rabbits
- the warmer parts of their body are light and the colder parts like nose, feet and ears are dark
50
Example of environmental influence: conditional lethality
- an allele is only lethal under certain conditions
- permissive conditions: conditions under which the individual survives
- restrictive conditions: conditions under which the individual dies
ex: fruit flies, if temp too high for a bit they become reversibly paralyzed, but if for a few hours they die
51
What shapes are males and females in a pedigree analysis?
male- square
female- circle
52
difference between breeding/punnet squares and pedigrees
Breeding- inbred lines and no new individuals, all descendants
Pedigrees- new individuals added each generation, not everyone in it is a descendant of someone else in the pedigree
53
Many human traits run in families, but most do not show simple mendelian inheritance. why?
multiple genes affecting the trait
- most confirmed single-gene traits humans are rare
54
Even with single-gene traits, determining inheritance pattern in humans can be challenging compared to peas, why?
- environmental effect
- not many offspring
55
Examples of single-gene traits in humans (3)
Albinism
- missing enzyme for melanin production
Cystic fibrosis
- non- functional CFTR gene, responsible for moving salt/water in and out of cells
- lungs, pancreas and other organs become clogged with thick mucus
Huntington disease
- abnormal protein important for neurons
56
Albinism
- usually recessive epistatic
-- eg: mm= albino then M_= various shades -> doesn't matter
57
Cystic fibrosis
- recessive trait
- one functional copy is enough to help function properly
- parents are often unaffected by heterozygous carriers for the recessive allele
- can skip generations
58
In a pedigree a HORIZONTAL pattern of inheritance is indicative of what?
a **rare recessive** trait
- lots of skips then in one generation see more then one affected individual
59
Huntington disease
- dominant trait
- the abnormal Htt protein damages nerve cells, even when the normal protein is also present (i.e. in heterozygotes)
-- this is why Huntington is dominant over the wild type allele
- Huntington is fatal but usually only after the person has had the chance to reproduce
- every person affected has at least one parent affected
60
a VERTICAL pattern of inheritance is indicative of what?
a **rare dominant** trait
61
Why can there not be dominant trait carriers?
because if an individual has just 1 copy they will have that trait
62
Three key characteristics of pedigrees with dominant traits
1. Affected children always have at least one affected parent
2. As a result, dominant traits show a vertical pattern of inheritance
3. Two affected parents can produce unaffected children, if both parents are heterozygotes
63
Three key characteristics of pedigrees with recessive traits
1. Affected individuals can be the children of two unaffected carriers, particularly as a result of consanguineous (between relatives) mating
2. all the children of two affected parents should be affected
3. rare recessive traits show horizontal pattern of inheritance
- recessive traits may show vertical if trait is extremely common in the population
64
**Autosomal trait**
trait that is conferred by a gene residing on a chromosome that is NOT involved in sex determination (i.e. chromosomes 1-22 in humans)
65
**Sex-linked trait**
trait that is conferred by a gene residing on a sex chromosome (i.e. the X or Y chromosome in humans)
66
Y linked traits always come from ____
dads
67
X linked traits come from...
for a son- mother
daughter- 50/50
68
Can males be carriers of x-linked traits?
No, they will show the gene
69
2 examples of x linked traits in humans
- red-green colour blindness
- hemophilia (improper blood clotting)
70
For x-linked recessive, who is more likely to be affected?
Be carriers?
- Males are more likely to be affected because they only need 1 copy
-Females are carriers because they need 2 to be affected
71
How are females affected for X-linked dominant traits? Can they be carriers?
- double the chances of them getting it
- they cannot be carriers because they will have it
72
Pedigree pattern: X-linked recessive
- trait never passes from a male to their male offspring
- female offspring of affected males are aways carriers
- 1/2 of male offspring of female carriers will inherit the trait
73
Pedigree pattern: X-linked dominant
- trait seen in every generation (no carriers)
- trait never passes from a male to their male offspring
- for affected males, 100% of their female offspring will be affected
74
Pedigree pattern: Y-linked
- only affects males
- no carriers
75
Chromosomal theory of inheritance
- heredity information is included on genes, and genes are located on chromosomes
- eggs and sperm contribute equally to the genetics of offspring through their nuclei
76
How do you make a karyotype?
take pictures of the chromosomes, cut them out and arrange them.
- always uses metaphase chromosomes and somatic cells (not gametes)
77
heterogametic
Males XY- 1 of each sex chromosome
78
homogametic
female XX- 2 of the same sex chromosomes
79
What do ZZ and ZW stand for?
ZZ is male
and ZW is female
when it is the reverse from us
80
In males as long as there is _____ the individual is male
1 Y
- even if 3 X
81
In drosophila it is the number of what that determines sex?
X chromosomes
- at least 2 X chromosomes, the individual is female
82
Mitosis
nuclear division that results in 2 daughter cells, each containing identical numbers of chromosomes to the parent cell
- produces clones of the parent cell
83
Meiosis
nuclear division that produces egg and sperm cells, each containing 1/2 the numbers of chromosomes found in other (somatic) cells
- produces cells that unique compared to parent cell
84
Somatic cells
everything other than sperm and egg
85
gametes
sperm and egg
86
Diploid
Most body cells are diploid (2n)
- diploid cells have two complete sets of chromosomes
- each chromosome pair includes one from each parent
- mitosis produces diploid cells from a diploid parent cell
87
Haploid
meiosis produces haploid (n) gametes
- haploid cells have one copy of each chromosome
88
In humans 2n= and n=
2n=46
n=23
n= the number of chromosomes in a normal gamete
89
What is a chromatid?
- a chromatid is one copy of a newly copied chromosome that is still joined to the other copy by a single centromere
-- you only really "see" chromosomes right before cell division
90
Nonhomologous chromosmes
- contain different genes
- do not pair at meiosis
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Homologous chromosomes
- members of a chromosome pair
- contain the same genes (can be different alleles, though)
- pair at meiosis
92
Sister chromatids
- identical copy of an individual chromosome
- identical alleles for all genes
93
Terminally differentiated cells...
stop dividing and enter the G0 stage
94
What are the stages of the cell cycle
Interphase
- G1 (or G0)
- S
- G2
M
- mitosis, cytokinesis
95
G1
Interphase gap 1 or gap 1 phase
- cells are actively producing products specific to their biological role in the body
- varies in length, depending on cell type
- some cells do not divide and stay in G1 (in which case it gets termed G0)
96
S phase
DNA Synthesis
- duplication (synthesis) of chromosomes to produce identical sister chromatids
- sister chromatids remain joined at the centromere
- DNA must be "open" for replication, not condensed
- in animal cells, centrosomes (structures involved in cell division) also need to replicate to produce two centrosomes
97
G2
Interphase gap 2 or gap 2 phase
- phase just before mitosis
- cell synthesis proteins necessary for mitosis and cell division are produced
98
Mitosis vs. Binary fission
Mitosis is a eukaryotic process
- eukaryotic nuclei typically have multiple linear chromosomes
cell division/reproduction happens via binary fission in prokaryotes
- prokaryotes do not have nuclei and usually have a single circular chromosome
99
5 stages of Mitosis
Prophase
- chromosomes condense and become visible
Prometaphase
- nuclear envelope breaks down, spindle forms, and sister chromatids attach to microtubules from opposite centrosomes
Metaphase
- chromosomes align at the cell equator
Anaphase
- sister chromatids separate and move to opposite poles
Telophase
- spindle disappears, chromosomes decondense, and are enclosed in two nuclei
100
Prophase
- chromosomes condense and become visible
- two centromeres (formed during S phase) move apart, one migrating to each pole of the cell
- microtubules (protein) begin to extend from centromeres
- nucleoli begin to disappear (distinct region of nucleus where ribosomes live)
101
Centrosome
= 2 centrioles (attached to spindle fibers) plus other proteins
102
Prometaphase
- nuclear membrane breaks down
- microtubules from centrosomes attach to **kinetochores** in the centromere of each sister chromatid
-- sister chromatids attach to microtubules form opposite poles
-- three types of microtubules, all originating from the centrosome, form the mitotic spindle:
--- Kinetochore microtubules attach to kinetochores
--- polar microtubules are directed to the middle of the cell
- astral microtubules extend toward the cells periphery
103
Centromere
region of DNA
104
Kinetochore
protein structure on the DNA that attaches to the microtubules
105
Metaphase
- chromosomes align on the *metaphase plate*
- sister chromatids face opposite poles of the cell
- forces pushing/pulling chromosomes to or from each pole are balanced, which keeps chromosomes in place
106
Anaphase
- sister chromatids of all chromosomes simultaneously separate at their centromere
- separated sister chromatids move to opposite poles via shortening kinetochore microtubules - disjunction
-- chromatids have a characteristic "v shape" at this stage
107
Telophase
- nuclear membrane (envelope) forms around each group of chromatids
- nucleoli re-form
- spindle fibers disappear
- chromosomes uncoil and reform as chromatin
108
Cytokinesis
- after mitosis
- cytoplasm of parent cell splits into two daughter cells with identical nuclei
- begins during anaphase, but isn't complete until after telophase
109
Cell cycle regulation
- at each checkpoint, signals are produced if prior events are not completed, which prevents the next step of the cycle from beginning
- checkpoints are critical to helping prevent errors in the cell cycle
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