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A-LEVEL BIOLOGY > Inheritance > Flashcards

Inheritance Flashcards

1
Q

diploid cell

A

is a cell that contains two complete sets of chromosomes (2n)

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2
Q

A diploid cell in the human body has how many chromosomes

A

46

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3
Q

haploid cells

A

contain one complete set of chromosomes (n), they have half the number of chromosomes compared to diploid cells

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4
Q

haploid cells are called

A

gametes

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5
Q

The need for reduction division during meiosis

A

-During fertilization the nuclei of gametes fuse together to form the nucleus of the zygote
-Both gametes must contain the correct number of chromosomes in order for the zygote to be viable. If a zygote has too many or too few chromosomes it may not survive
-For a diploid zygote this means that the gametes must be haploid
-Meiosis produces haploid gametes during sexual reproduction

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6
Q

The first cell division of meiosis is

A

a reduction division

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7
Q

Homologous chromosomes

A

-Carry the same genes in the same positions
-Are the same shape

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8
Q

Although homologous pairs of chromosomes contain the same genes in the same order they don’t necessarily carry

A

the same alleles

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9
Q

Meiosis has two divisions

A

meiosis I and meiosis II

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10
Q

Prophase I

A

-DNA condenses and becomes visible as chromosomes
-DNA replication has already occurred so each chromosome consists of two sister chromatids joined together by a centromere
-The chromosomes are arranged side by side in homologous pairs- a pair of homologous chromosomes is called a bivalent
-As the homologous chromosomes are very close together the crossing over of non-sister chromatids may occur. The point at which the crossing over occurs is called the chiasma (chiasmata; plural)
-In this stage centrioles migrate to opposite poles and the spindle is formed
-The nuclear envelope breaks down and the nucleolus disintegrates

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11
Q

Metaphase I

A

The bivalents line up along the equator of the spindle, with the spindle fibres attached to the centromeres

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12
Q

Anaphase I

A

-The homologous pairs of chromosomes are separated as microtubules pull whole chromosomes to opposite ends of the spindle
-The centromeres do not divide

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13
Q

Telophase I

A

-The chromosomes arrive at opposite poles
-Spindle fibres start to break down
-Nuclear envelopes form around the two groups of chromosomes and nucleoli reform
-Some plant cells go straight into meiosis II without reformation of the nucleus in telophase I

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14
Q

Cytokinesis I

A

-This is when the division of the cytoplasm occurs
-Cell organelles also get distributed between the two developing cells
-In animal cells: the cell surface membrane pinches inwards creating a cleavage furrow in the middle of the cell which contracts, dividing the cytoplasm in half
-In plant cells, vesicles from the Golgi apparatus gather along the equator of the spindle (the cell plate). The vesicles merge with each other to form the new cell surface membrane and also secrete a layer of calcium pectate which becomes the middle lamella.
-Layers of cellulose are laid upon the middle lamella to form the primary and secondary walls of the cell
-The end product of cytokinesis in meiosis I: two haploid cells
-These cells are haploid as they contain half the number of centromeres

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15
Q

Why is the DNA not replicated between meiosis I and meiosis II

A

because there is no interphase between the two stages

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16
Q

Meiosis II is nearly identical to

A

the stages of mitosis

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17
Q

Prophase II

A

-The nuclear envelope breaks down and chromosomes condense
-A spindle forms at a right angle to the old one

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18
Q

Metaphase II

A

Chromosomes line up in a single file along the equator of the spindle

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19
Q

Anaphase II

A

-Centromeres divide and individual chromatids are pulled to opposite poles
-This creates four groups of chromosomes that have half the number of chromosomes compared to the original parent cell

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20
Q

Telophase II

A

Nuclear membranes form around each group of chromosomes

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21
Q

Cytokinesis II

A

-Cytoplasm divides as new cell surface membranes are formed creating four haploid cells
-The cells still contain the same number of centromeres as they did at the start of meiosis I but they now only have half the number of chromosomes (previously chromatids)

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22
Q

The distinguishing features at each stage of Meiosis I

A

Prophase I: Homologous pairs of chromosomes are visible
Metaphase I: Homologous pairs are lined up side by side along the equator of the spindle
Anaphase I: Whole chromosomes are being pulled to opposite poles with centromeres intact
Telophase I: There are 2 groups of condensed chromosomes around which nuclei membranes are forming
Cytokinesis: Cytoplasm is dividing and the cell membrane is pinching inwards to form two cells

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23
Q

The distinguishing features at each stage of Meiosis II

A

Prophase II: Single whole chromosomes are visible
Metaphase II: Single whole chromosomes are lined up along the equator of the spindle in single file (at 90 degree angle to the old spindle)
Anaphase II: Centromeres divide and chromatids are being pulled to opposite poles
Telophase II: Nuclei are forming around the 4 groups of condensed chromosomes
Cytokinesis: Cytoplasm is dividing and four haploid cells are forming

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24
Q

Independent assortment

A

the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase I

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25
Why independent assortment occurs
-Each pair can be arranged with either chromosome on top, this is completely random -The orientation of one homologous pair is independent/unaffected by the orientation of any other pair
26
The combination of alleles that end up in each daughter cell depends on
how the pairs of homologous chromosomes were lined up
27
How random fusion of gametes during fertilisation results in genetic variation
-During fertilization any male gamete can fuse with any female gamete to form a zygote -This creates genetic variation between zygotes as each will have a unique combination of alleles -There is an almost zero chance of individual organisms resulting from successive sexual reproduction being genetically identical
28
gene
A length of DNA that codes for a single polypeptide or protein
29
locus (plural: loci)
The position of a gene on a chromosome
30
alleles
two or more different forms of the same gene
31
Different alleles of a gene have
slightly different nucleotide sequences but they still occupy the same position (locus) on the chromosome
32
Because they are two copies of a gene present in an individual that means
there can be different allele combinations within an individual
33
genotype
the alleles of a gene possessed by that individual
34
homozygous
When the two allele copies are identical in an individual
35
heterozygous
When the two allele copies are different in an individual
36
The genotype of an individual affects their
phenotype
37
phenotype
the observable characteristics of an organism
38
alleles that are dominant
are always expressed in the phenotype whether it's an hetrozygous or homozygous organism
39
recessive alleles are expressed in the phenotype when
there's no dominant allele present- only when homozygous recessive
40
codominance
when both alleles can be expressed in the phenotype at the same time
41
F1 generation
the offsprings resulting from when a homozygous dominant individual is crossed with a homozygous recessive individual
42
All of the F1 generation are
heterozygous
43
F2 generation
the offsprings produced from crossing two individuals in the F1 generation
44
How a test cross can be used to try and deduce the genotype of an unknown individual that is expressing a dominant phenotype
-The individual in question is crossed with an individual that is expressing the recessive phenotype -The resulting phenotypes of the offspring provide sufficient information to suggest the genotype of the unknown individual
45
How to deduce the genotype of the dominant phenotype in a monohybrid test cross
-If no offspring exhibit the recessive phenotype then the unknown genotype is homozygous dominant -If at least one of the offspring exhibit the recessive phenotype then the unknown genotype is heterozygous
46
How to deduce the genotype of the dominant phenotype in a dihybrid test cross
-If no offspring exhibit the recessive phenotype for either gene then the unknown genotype is homozygous dominant for both genes -If at least one of the offspring exhibit the recessive phenotype for one gene but not the other, then the unknown genotype is heterozygous for one gene and homozygous dominant for the other -If at least one of the offspring exhibit the recessive phenotype for both genes then the unknown genotype is heterozygous for both genes
47
The two sex chromosomes
X and Y
48
sex-linked genes
the inheritance of genes that are dependent on the sex of the individual
49
Most often sex-linked genes are found on
the longer X chromsome
50
Haemophilia
-a well-known example of a sex-linked disease -an inherited bleeding disorder in which the blood does not clot properly
51
autosomes
any chromosome that isn’t a sex chromosome
52
Autosomal linkage
-Two or more genes on the same chromosome do not assort independently during meiosis -These genes are linked and they stay together in the original parental combination
53
Monohybrid inheritance
looks at how the alleles for a single gene are transferred across generations
54
Genetic diagrams
often used to present known information about genotypes, phenotypes and the process of meiosis in a clear and precise manner so that predictions about the phenotype of the offspring can be made- an example is the punnett square
55
The predicted genotypes that genetic diagrams produce are all based on
chance- there is no way to predict which gametes will fuse so sometimes the observed or real-life results can differ from the predictions
56
The possible phenotypes for sex-linked genes in females
normal, carrier and has the disease
57
The possible phenotypes for sex-linked genes in males
normal or has the disease
58
Dihybrid Inheritance
looks at how the alleles of two genes transfer across generations
59
Epistasis
when two genes on different chromosomes affect the same feature
60
recombinant offsprings
offsprings that have a different combination of characteristics to their parents
61
parental type offsprings
offsprings that have the same combination of characteristics as their parents
62
why recombinant offspring can be produced in real life despite the presence of autosomal linkage
This is due to the crossing over that occurs during meiosis. The crossing over and exchanging of genetic material breaks the linkage between the genes and recombines the characteristics of the parents.
63
chi-squared test
A statistical test that determines whether there is a significant difference between the observed and expected results in an experiment
64
The chi-squared test is completed when
the data is categorical (data that can be grouped)
65
How to calculate chi-squared values
-Obtain the expected and observed results for the experiment -Calculate the difference between each set of results -Square each difference (as it is irrelevant whether the difference is positive or negative) -Divide each squared difference by the expected value and get a sum of these answers to obtain the chi-squared value
66
χ2
Σ(O-E)^2/E
67
Analysing chi-squared values
-To work out what the chi-squared value means, a table that relates chi-squared values to probabilities is used -If the chi-squared value represents a larger probability than the critical probability then it can be stated that the differences between the expected and observed results are due to chance -If it represents a smaller probability than the critical probability then the differences in results are significant and something else may be causing the differences -To determine the critical probability biologists generally use a probability of 0.05 (they allow that chance will cause five out of every 100 experiments to be different) -The number of comparisons made must also be taken into account when determining the critical probability. This is known as the degrees of freedom
68
how degrees of freedom can be worked out
by subtracting one from the number of classes
69
Humans with albinism lack
the pigment melanin in their skin, hair and eyes; this causes them to have very pale skin, very pale hair and pale blue or pink irises in the eyes
70
the metabolic pathway for producing melanin
1) The amino acid tyrosine is converted to DOPA by the enzyme tyrosinase 2) DOPA is converted to dopaquinone again by the enzyme tyrosinase 3) Dopaquinone is converted to melanin
71
What gene codes for enzyme tyrosinase
gene TYR located on chromosome 11
72
the recessive allele for the gene TYR causes
- causes a lack of enzyme tyrosinase or the presence of inactive tyrosinase -without the tyrosinase enzyme tyrosine can not be converted into melanin
73
Sickle cell anaemia
-a condition that causes individuals to have frequent infections, episodes of pain and anaemia -humans with sickle cell anaemia have abnormal haemoglobin in their red blood cells
74
What gene codes for β-globin polypeptide found in haemoglobin
gene HBB which is found on chromosome 11
75
The abnormal allele for the gene HBB produces
-the change of a single base in the DNA of the abnormal allele results in an amino acid substitution (the base sequence CTC is replaced by CAC) -a slightly different amino acid sequence to the normal allele -the change in amino acid sequence (the amino acid Glu is replaced with Val) results in an abnormal β-globin polypeptide
76
abnormal β-globin in haemoglobin affects
the structure and shape of the red blood cells: ~They are pulled into a half-moon shape ~They are unable to transport oxygen around the body ~They stick to each other and clump together blocking capillaries
77
Factor VIII
a coagulating agent that is needed to make blood clot
78
the gene that codes for Factor VIII protein
F8, a gene present on the X chromosome making F8 a sex-linked gene
79
abnormal alleles of the F8 gene result in
-Production of abnormal forms of factor VIII -Less production of normal factor VIII -No production of factor VIII
80
lack of normal factor VIII
-prevents normal blood clotting -causes the condition haemophilia
81
Huntington’s disease
- a genetic condition that develops as a person ages -usually, a person with the disease will not show symptoms until they are 30 years old + -an individual with the condition experiences neurological degeneration; they lose their ability to walk, talk and think -the disease is ultimately fatal
82
Individuals with Huntington's disease have an abnormal allele of which gene
HTT gene
83
HTT gene codes for
-the protein huntingtin which is involved in neuronal development -people that have a large number (>40) of repeated CAG triplets present in the nucleotide sequence of their HTT gene suffer from the disease
84
Which allele is dominant in Huntingtin's disease
The abnormal allele is dominant over the normal allele so, if an individual has one abnormal allele present they will suffer from the disease
85
What gene dictates the height of some plants
Le
86
The two alleles of the Le gene
dominant allele Le produces tall plants when present recessive allele le produces shorter plants when present (in a homozygous individual)
87
What does the Le gene regulate
the production of an enzyme that is involved in a pathway that forms active gibberellin GA1
88
Gibberellin
-a hormone that helps plants grow by stimulating cell division and elongation in the stem -can also control seed germination in plants (eg: wheat and barley) by stimulating the synthesis of the enzyme amylase
89
recessive allele le is
-only one nucleotide different to the dominant allele -this causes a single amino acid substitution (threonine -> alanine) in the primary structure of the enzyme -this change in primary structure occurs at the active site of the enzyme, making it non-functional so non-functional enzymes are produced
90
Plants that are homozygous for the recessive allele le are
dwarves
91
structural gene
codes for a protein that has a function within a cell
92
regulatory gene
codes for a protein that helps to control the expression of another gene
93
How the expression of enzyme-producing genes can be controlled
using inducible or repressible enzymes
94
Inducible enzymes
are enzymes that are only synthesized when their substrate is present; the presence of the substrate induces the synthesis of the enzyme by causing the transcription of the gene for the enzyme to start
95
Repressible enzymes
are enzymes that are synthesized as normal until a repressor protein binds to an operator; the presence of the repressor protein represses the synthesis of the enzyme by causing the transcription of the gene for the enzyme to stop
96
Why controlling when enzymes are produced is beneficial for cells
stops materials and energy from being wasted; for example, using materials and energy to synthesize an enzyme when its substrate is not present and it can’t carry out its function would be highly wasteful
97
operon
a group or a cluster of genes that are controlled by the same promoter in prokaryotes
98
lac operon
controls the production of the enzyme lactase (also called β-galactosidase) and two other structural proteins
99
Lactase
-breaks down the substrate lactose so that it can be used as an energy source -is an inducible enzyme that is only synthesized when lactose is present
100
Promoter
Region of DNA required to allow transcription of the gene to take place
101
Operator
Segment of DNA to which repressor binds to inhibit transcription of gene
102
components of the lac operon
-Promoter for structural genes -Operator -Structural gene lacZ that codes for lactase -Structural gene lacY that codes for permease (allows lactose into the cell) -Structural gene lacA that codes for transacetylase
103
Located to the left (upstream) of the lac operon on the bacterium's DNA there is also the
-Promoter for regulatory gene -Regulatory gene lacI that codes for the lac repressor protein
104
The two binding sites on the lac repressor protein
-it can bind to the operator and thus prevent the transcription of the structural genes as RNA polymerase cannot attach to the promoter -it can bind to lactose (the effector molecule) so that its shape gets distorted and it can no longer bind to the operator
105
when lactose is absent in the medium that the bacterium is growing in | regulation of structural gene that produces lactase enzyme
1)The regulatory gene is transcribed and translated to produce lac repressor protein 2)The lac repressor protein binds to the operator region upstream of lacZ 3)Due to the presence of the repressor protein RNA polymerase is unable to bind to the promoter region 4)Transcription of the structural genes does not take place 5)No lactase enzyme is synthesized
106
when lactose is present in the medium that the bacterium is growing in | regulation of structural gene that produces lactase enzyme
1)There is an uptake of lactose by the bacterium 2)The lactose binds to the second binding site on the repressor protein, distorting its shape so that it cannot bind to the operator site 3)RNA polymerase is then able to bind to the promoter region and transcription takes place 4)The mRNA from all three structural genes is translated 5)The enzyme lactase is produced and lactose can be broken down and used for energy by the bacterium
107
The genetic control of a repressible enzyme
- It's the opposite of the lac operon(inducible enzyme): when there is less of the effector molecule, the repressor protein cannot bind to the operator region and transcription of the structural genes goes ahead, meaning the enzyme is produced -In this mechanism, an effector molecule also binds to a repressor protein produced by a regulatory gene. However, this binding actually helps the repressor bind to the operator region and prevent transcription of the structural genes
108
transcription factor
-a protein that controls the transcription of genes by binding to a specific region of DNA in eukaryotes -ensure that genes are being expressed in the correct cells, at the correct time and at the right level
109
What's the percentage of genes in humans that are thought to code for transcription factors
10%
110
How transcription factors work
-Some transcription factors bind to the promoter region of a gene thus allowing or preventing the transcription of the gene from taking place -The presence of a transcription factor will either increase or decrease the rate of transcription of a gene; for example, PIF is a transcription factor found in plants that activates the transcription of the amylase gene
111
components involved in gibberellin gene control
-Repressor protein DELLA -Transcription factor PIF -Promoter of amylase gene -Amylase gene -Gibberellin -Gibberellin receptor and enzyme
112
process of gibberellin gene control
1)DELLA protein is bound to PIF, preventing it from binding to the promoter of the amylase gene so no transcription can occur 2)Gibberellin binds to a gibberellin receptor and enzyme which starts the breakdown of DELLA 3)PIF is no longer bound to DELLA protein and so it binds to the promoter of the amylase gene 4)Transcription of the amylase gene begins and amylase is produced
113
why RNA analysis is important with regard to gene expression
When a cell expresses a gene, RNA is produced by transcription. This RNA present in a cell can be analysed. Scientists can then match the RNA present in a cell to specific genes and work out which genes are being expressed in that specific cell

A-LEVEL BIOLOGY (8 decks)

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