Genetic Variation Flashcards
(115 cards)
1
Q
Practical: measuring variation of hand angles
A
- trace your hand on a piece of paper
- using a ruler and protractor, determine your hand angle
d1=d4
d2=d5
angle between d4 and d5= hand angle
2
Q
Method for table and histograms
A
- Hand angle range: group of angles that students measure, in 5 degree increments
e.g. 0-5°, 6-10°, 11-15° - Total students whose hand angle is within the range
- Total number of students
- Hand angle frequency: percentage of students in each angle range.
3
Q
frequency percentage formula
A
frequency % =
number of students for a specific hand angle range / total number of students
x100
4
Q
Continuous variations
A
have a wide distribution of traits
e.g. color skin and hair, height
5
Q
Discontinuous variations
A
only have a few, discrete traits
e.g. cleft chin or no cleft chin, blood type either
+ or -
6
Q
Continuous variation plotted
A
- plotted on histograms
-> histogram: shows range and frequency of variation from one extreme to another - curve that the graph produces = normal distribution
7
Q
Discontinuous variation plotted
A
- plotted on bar graphs
-> bar graph: shows variation is either one type or another type
8
Q
Charles Darwin: “decent with modification”
A
offspring inherit their traits from their parents, they don’t look the same as their parents or siblings.
9
Q
What term best describes “naturally inherited differences in a population”?
A
Genetic variation
10
Q
list 5 examples of variation in humans
A
- hair color
- height
- eye color
- blood type
- skin color
11
Q
where does variation in population come from?
A
- mutations
- environmental factors like climate
12
Q
Law of segeregation
A
the 2 copies (types) of each inherited factor (genes) for a trait randomly separate during the formation of gametes (egg and sperm), so that either copy has the same change (50 50) of being inherited by the offspring
13
Q
Law of independent assortment
A
inheriting a copy of an inherited factor (genes) for one trait has nothing to do with inheriting copies of other inherited factor for any other traits
14
Q
True-breeding
A
parents that produce offspring with the same variation (type) of a trait
(e.g. homozygous dominant BB., TT always produce black/tall offspring)
15
Q
Mendel’s experiment
A
- true-breeding pea plants that have offspring with same type (e.g. plants that produce offspring with only yellow peas)
- crossbred true-breeding pea plants that have same trait but of 2 different varieties (e.g. crossbred true-breeding yellow peas with true-breeding green peas)
- he then crossed the offspring to see what would happen in the 2nd generation
16
Q
genes
A
inherited factors (e.g. eye color, hair color)
17
Q
alleles
A
the different variations (type) of genes (e.g. blue eyes vs black eyes)
18
Q
genotype
A
the combination of alleles
3 possible genotypes:
YY
yy
Yy
19
Q
homozygous dominant
A
genotypes with 2 of the same alleles (YY)
20
Q
heterozygous
A
genotypes with 2 different alleles (Yy)
21
Q
homozygous recessive
A
genotypes with 2 recessive alleles (yy)
22
Q
there are no genotypes called:
A
- heterozygous dominant
- heterozygous recessive
anything heterozygous basically
23
Q
phenotypes
A
the physical appearance of the trait
2 possible phenotypes:
- dominant phenotype (YY or Yy)
- recessive phenotype (yy)
24
Q
what happens to the recessive traits?
A
each of e.g. plants in the new generation could carry the allele for the recessive trait within it, but the effect of this allele is not seen in the appearance of the individual
25
how many pairs of chromosomes do humans have?
23 pairs
- each individual has 2 copies of chromosomes, each copy inherited from each parent.
26
what's the greatest difference between any 2 individuals?
their biological sex
- offspring inherit one sex chromosome from each parent
27
what is the gene that makes a baby become biologically male?
the gene called SYR located on the y chromosome that causes the foetus to become biologically male
28
what do offspring inherit from their parents?
offspring inherit one sex chromosome X OR Y from each parent
female = XX
male = XY
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x-linked inheritance
Females (XX): have 2 alleles for every x-linked gene, one one each chromosome (so if one gene has a problem, the other X can "cover it up.")
Males (XY) only have 1 allele for every x-linked gene (if their X has a problem, they don't have a backup—which means they will show the trait.)
This means males and females inherit X-linked traits differently!
30
x-linked genes
(genes found on the x-chromosome)
31
what trait is color blindness?
females and males have how many alleles for this gene?
color blindness is an x-linked recessive trait.
- females have 2 alleles for this gene
- males only have one allele for this gene
32
2 alleles for colorblind trait:
NOTE: X for the male or female chromosome
n/N dominant or recessive alleles
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hemizygous
only one allele is present
34
Possible genotypes and phenotypes for color blind trait?
color blindness is a recessive trait, so it will only be displayed if there's no dominant allele in the genotype.
XNXN = homozygous dominant = female normal vision
XNXn= heterozygous = female normal vision
XnXn = homozygous recessive = female color blind
XNY = hemizygous dominant = male normal vision
XnY= hemizygous recessive = male color blind
35
why is it easier for the males to be color blind?
Since males (XY) only have one X chromosome, they only need one faulty gene to be color blind.
Females (XX) need two faulty genes (one from each parent) to be color blind.
36
which parent influences males to be colorblind?
only the mother's genotype influences the male's x linked genotype (color blind XnY) since male offspring get their x-chromosome (XY) from their mother.
their father ONLY passes on the Y chromosome, but not the x-linked genotype. (children don't get their father's x chromosomes!!! even if they are color blind)
37
what trait is vitamin D-resistant rickets?
females and males have how many alleles for this gene?
vitamin D-resistant rickets is an x-linked dominant trait
- females have 2 alleles for this gene
- males only have one allele for this gene
38
2 alleles for rickets trait:
dominant: X^R
recessive: X^r
(since it's dominant now)
39
what happens if a female with normal vision (XNXN) and a color blind male (XnY) have male children? what genes will the boys inherit?
the boys will not be color blind and the disorder will not appear in subsequent generations unless it is re-introduced.
40
pedigree charts
chart used to determinate inheritance patterns of traits through several generations of a family
41
what are carriers and their genotype? (for x linked recessive traits)
carriers are heterozygous for x linked recessive traits (XAXa), they carry the trait
-> males can't be carries., they can't pass on x-linked traits
-> carries have the gene, but they DON't show it and have the condition (XAXa) but can pass it on
42
in pedigree charts, how do you know if a trait is dominant or recessive?
a trait is recessive if it skips generations
43
Inheritance patterns
- dominant traits never skips generations. recessive can!
- dominant traits once lost from a lineage, will never reappear
- x-linked traits sons only inherit traits from their mothers
44
DNA describe ladder
- can be described as a twisted ladder
- upright of ladder (blue): made of sugar and phopsate
- rungs (red and green): nitrogen rich bases
45
4 nitrogen-rich bases
1. adenine
2. thymine
3. guanine
4. cytosine
46
what are the complementary base pairings? why?
A-T
G-C
this is due to their specific shapes
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What is DNA made of?
DNA is made of billions of smaller subunits called nucleotides
48
what does each nucleotide consist of?
- a phosphate group
- a deoxyribose sugar
- one of the four nitrogen rich bases
phosphate and deoxyribose sugar is the same in ever DNA nucleotide
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what are genes in DNA?
genes are specific sequences of DNA
genetic information is coded in the order of A,T,C AND G
50
Where is DNA located in chromosomes?
DNA is tightly packed into chromosomes which are found in the nucleus of a cell.
51
How many chromosomes in humans? describe.
what is it called when both chromosomes are the same? give examples
- Humans have 46 chromosomes, 23 pairs
- one copy inherited from mother, other copy inherited from father
- when both chromosomes are the same, they are called homologous chromosome pairs
- autosomes: (non-sex chromosomes)
all pairs of autosomes are homologous
female= sex chromosomes are homologous
male= sex chromosomes are non-homologous
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Homologous chromosomes have the same:
Homologous chromosomes have the same:
- length
- shape
- genes located on them (they may have different alleles of these genes)
53
Diploid cells
2n
- humans body cells are diploid since they contain 23 chromosome pairs (22 homologous pairs of autosomes, 1 pair of sex chromosomes)
- diploid number of human cells are 46
- different species have different diploid numbers e.g. chimps = 2n=48
-> all diploid numbers are even
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Haploid cells
1n
- human gametes (sperm and eggs) are haploid since they contain 23 chromosome (22 autosomes, 1 sex chromosome)
- haploid number of human gametes is 23
- differeterm-55nt specieis have different haploid numbers e.g. chimp= 24
-> all haploid numbers are odd or even
55
Protein
create body structures and perform different functions in your cells, resulting in all your phenotypes like hair color
56
Describe Recessive and dominant alleles
- sometimes the different version of the protein is worse at doing its job (recessive allele)
- sometimes the different version of the protein is better at doing its job (dominant allelle)
- different alleles for the same gene produce slightly different versions of the same protein (basically describing what an alelle is)
57
the more efficient protein =
results in the dominant trait
58
how are alleles formed?
DNA mutations (small changes in the DNA sequence)
-> can change from one letter!
59
how do the letters in DNA code spontaneously change?
give 3 examples
mutagens
example of mutagens (3)
1. UV radiation from the sun
2. Certain chemicals like cigarettes and vapes
3. Radiation from radioactive isotopes
60
how many letters in genetic codes?
genetic code is written in 3 lettered-words
61
what are the 4 types of DNA mutations?
1. silent mutations
2. missense mutation
3. nonsense mutation
4. frameshift mutation
62
link genes, DNA and proteins
our genes are made of DNA ->
our genes are made of DNA ->
DNA has instructions for building proteins ->
proteins are important, they help perform functions for e.g. hair color
genes make protein
63
silent mutation
the DNA change that doesn't alter the protein
- these are changes in the genetic code which don't affect the individual.
- they occur when a nitrogen base on the DNA strand is changed and this doesn't affect the protein that is made.
(For example, if the codon GAA (which codes for the glutamic acid) is changed to GAG, it still codes for glutamic acid. Therefore, the protein's function remain unchanged.)
64
missense mutation
the DNA change that alters the protein at one point
- changes that don't stop the gene from making a protein ( like nonsense mutation), but the protein produced is a different one
- protein may not function correctly and cause a disease. it is possibly responsible for sickle-cell anaemia
65
nonsense mutation
the DNA change stops the protein from being made past a certain point
- causes the cells to stop reading the info on the gene before it ends
(THESE WORS AR)
- protein created is incomplete and can't function at all
e.g. cystic fibrosis, duchenne muscular
66
frameshift mutation
when a letter/one or more bases is inserted or deleted, severely altering the protein
- causes all the info following the deletion/insertion to become jumbled so that it can't be read to make a protein
- frameshift mutations frequently results in severe genetic diseases
e.g. Tay-Sachs disease
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harmful DNA mutations
- most DNA mutations are not harmful
68
What is albino?
recessive trait
- trait where melanin (color for humans) is NOT produced
- if you have more melanin cells, the darker your skin
- lack of melanin cells means albinos are whtie
69
what do DNA mutations produce?
DNA mutations produce the genetic variation required for evolution
70
what is albino caused by?
the recessive allele (a) is caused by missense mutation in a gene called TYR
71
Albinos possess which genotypes?
Can two non-albino parents have albino children? explain
albino = aa
non-albino =AA, Aa
yes, they could be carriers and both parents have to be heterozygous
72
What do cells have that can fix DNA mutations?
are most DNA mutations harmful?
- cells have DNA repair mechanisms that fix most
73
why do heterozygotes (Aa) demonstrate the dominant phenotype?
they demonstrate the dominant phenotype because they possess a copy of the dominant allele
74
what is the cell cycle?
the cell cycle is a series of events that take place as as cell grows and divides
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the 3 main phases in the cell cycle
1. interphase (preparation for division)
2. m phase (division of the nucleus)
3. cytokinesis (division of the cell)
I AM SIIIII(ck)
76
what does cytokinesis divide?
one parent cell divides into 2 daughter cells by the process of cytokinesis
77
process of interphase
G1= gap 1 phase
S= S phase
G2= gap 2 phase
m phase (mitosis or meiosis)
cytokinesis
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Interphase- Gap 1 phase
During G1 phase, the cell needs to grow to get large enough to divide.
10 hours
- nothing appears to happen under a microscope
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Interphase- S phase
During this phase, the DNA replicates so each daughter cell can inherit a full genome.
6 hours
- S stands for DNA synthesis
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Interphase- Gap 2 phase
In this phase, the organelles are replicated so that each daughter cell inherits all the cell structures
4 hours
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where is DNA located?
nucleus of a cell
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M phase - mitosis
## Footnote
how many hours?
Mitosis is the division of the diploid parent nucleus (original nucleus) that results in 2 diploid daughter nuclei
2 hours
83
where do the chromatids join?
in the centromere
84
Cytokinesis- cell division
cytokinesis is the final step of the cell cycle. the parent cells splits into 2 daughter cells
cytoplasm divides and results in 2 identical daughter cells.
85
what happens if mitosis happens without cytokinesis? where can this occur?
it results in a single cell with 2 nuclei. this can occur in some plant cells.
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what does mitosis produce?
one diploid parent cell produces...
2 diploid daughter cells
- the 2 daughter cells are identical to each other AND the parent cell
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What is mitosis used for?
1. growth of organisms: by making new cells
2. repairing tissues: by replacing old or damaged cells
3. asexual reproduction: by producing genetically identical offspring
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....
...
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what are the 4 phases of mitosis?
PMAT:
1. prophase
2. metaphase
3. anaphase
4. telophase
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Interphase: quick explanation overall
- you have a lot of DNA (inside nucleus) that you have put into your new cells, so DNA organized into units called chromosomes
the DNA coils up, chromosomes replicate to have 2 chromatids
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Prophase
chromosomes form, each now with 2 chromatids
-replicated chromosomes and their chromatids become visible
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Metaphase
(m for middle!)
-nucleus is gone because membrane surrounding nucleus break down
- chromosomes line-up along the cell equator, network of fibres appears, extending from the poles (ends) of the cell to each chromosome
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Anaphase
(a for away!)
- chromatids separate and move towards the cell's opposite poles: the 2 separated chromatids now 2 independent chromosomes
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Telophase
(two cells!)
- a new nuclear membrane encloses the chromosomes at each pole.
- 2 nuclei (nucleus!) formed, each with the same number of chromosomes as the parent cell.
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Cell Cycle for meiosis
Interphase
- gap 1 phase
- s phase
- gap 2 phase
M phase (meiosis)
Cytokinesis
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Meiosis
Meiosis is the division of the diploid parent nucleus that results in 4 haploid daughter nuclei and makes gametes (sperm and egg cells)
- the 4 daughter cells are different to each other and the parent cell
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What is meiosis used for?
It is used for creating gametes (sperm and egg cells
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why does there have to be half the diploid number in your gametes?
there has to be half the diploid number in your/each parent gametes (n)
- this is because if each parent passed on their complete set of genetic info (2n), their offspring will have 4n chromosomes, the next generation will have 8n so on...
- by halving the number of chromosomes in the gametes, the number of chromosomes from generation to generation is constant at 2n
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homologous pair
chromosomes roughly the same size, contain the same type of genes in the same locations. They crossover and transfer genetic information, this is how there is genetic variation in the world
(formed in meiosis after replication where from 46 chromatids, now 92 chromatids are made, it is paired up in 23s!)
100
in meiosis, one chromosome in each homologous pair must what?
one chromosome from each homologous pair must end up in each gamete produced, so the gametes have 23 chromosomes in total. (known as haploid number)
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Prophase 1 meiosis
chromosomes form, each now with 2 chromatids
(from 46 chromatids to 92 chromatids)
-replicated chromosomes and their chromatids become visible
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Metaphase 1 meiosis
replicated chromosomes form homologous pairs
- nuclear membrane breaks down
- homologous pairs line up on the equator of the cell
- attached to spindle fibres that extends from the poles to each chromosome pair
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Anaphase 1 meiosis
- fibres contracts and pulls one replicated chromosome from each pair to opposite poles of the cell
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Telophase 1/cytokinesis meiosis
- cell divides, producing 2 daughter cells
- only 1 copy from each homologous chromosome pair in each daughter cell
- each chromosome in this stage is still 2 chromatids
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Prophase 2 meiosis
no special events
- spindle fibres and chromosomes condense like in prophase 1
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Metaphase 2 meiosis
- new network of spindle fibres form at right angles to the first (vertical)
- fibres attach to the chromosomes lined up on the equator of the cell (this time the chromosomes are not in pairs, so now like mitosis)
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Anaphase 2 meiosis
- this time when the spindle fibres contract, the chromatids are pulled apart and move towards the poles of the cells
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Telophase 2 meiosis
- new nuclear membranes form
- cytoplasm divides to produce 4 new cells, each containing the haploid number of chromosomes
- these cells made are gametes or sex cells. in humans, the gametes have 23 chromosomes
109
what does meiosis lead to?
Variation?
leads to offspring variation
- each chromosome carries thousands of genes
- each gene has various alleles
- meiosis shuffles the alleles to produce genetic variation in the gametes
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why do identical twins from the same parent look the same?
identical twins look the same as they come from the same fertilized egg (zygote), so they share the same chromosomes from the same sperm and egg cell
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where does meiosis only occur in?
meiosis only occurs in gonads
female: ovary
male: testes
112
female eggs
females: egg cells (ova) are formed in the ovaries
- once a month, an egg cell is released from an ovary and enters the fallopian tube
113
male sperms
males: sperm cells formed in the testes
- sperm cells are stored in the epididymis
114
where does fertilization occur?
fertilization (egg+sperm) occurs in the fallopian tubes
- the zygote starts dividing from mitosis to become an embryo, which implants in the uterus
embryo continues dividing through mitosis to become a foetus
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how are twins created?
identical twins: when an early embryo splits into 2 groups of cells
