1
Q
Define sexual reproduction
A
- The reproduction involving the fusion of gametes to produce a zygote (fertilization)
2
Q
What is a gene
A
- A strand of DNA coding for one protein/polypeptide
3
Q
what are Haploid cells
A
These contain 1 complete set of chromosomes which are represented by “n”
They have 23 chromosomes
4
Q
What are diploid cells
A
These contain 2 complete sets of chromosomes usually represented by “2n”
they have 46 chromosomes
5
Q
What are homologous chromosomes
A
- 2 chromosomes that carry the same genes in the same positions and almost have the same size
6
Q
What is fertilisation
A
- The fusing of the nuclei of 2 gametes to form a zygote
7
Q
what refers to the locus
A
- The position of a gene on a chromosome
8
Q
Describe Meiosis
A
- A type of nuclear division that results in the production of 4 daughter cells with half the chromosome number of the parent cell with reshuffled alleles.
There are 2 phases; Meiosis 1 and Meiosis 2
Each has a : - Prophase
- Metaphase
- Telophase
- Anaphase
9
Q
What occurs in prophase I
A
(Early prophase I)
- Chromosomes condense and become visible.
(Middle prophase I) Synapsis:
- The homologous pairs will line up side by side and each pair is referred to as a bivalent
- Centrosomes move to opposite ends of the nucleus
( Late Prophase I)
- A chromatid of one of the pairs intertwines with the other chromatid and the crossing point is called a chiasma and there is always at least one.
- The crossing over of genes occurs when a part of a chromatid from one chromosome may break and rejoin with the chromatid.
10
Q
What occurs in Metaphase I
A
The spindle fibres now move the bivalents to the equator of the cell.
11
Q
What occurs in Anaphase I
A
- Unlike mitosis, the centromeres do not divide and instead, the whole chromosome moves towards opposite ends of the spindle
12
Q
What occurs in Telophase I
A
- The chromosomes have now arrived at opposite ends of the dividing cell and the spindle fibres now break down.
- The nucleus reforms and a reduction division has occured- Each new cell contains one complete set of chromosomes (one from each homologous
pair.) - Cytokinesis occurs
13
Q
what is the product of Meiosis II
A
- 4 haploid daughter cells that are not genetically identical are formed
14
Q
What is an allele
A
- A variation of a gene
15
Q
How is variation brought about in genes
A
-The crossing over
- Independent assortment
- random fertilisation
16
Q
describe independent assortment
A
- The ability of any allele to find itself in the same cell as any other allele is called independent assortment
- During metaphase 1, the alignment of bivalents on the equator of the cell is very random.
- As the homologous chromosomes are pulled apart, the combination of alleles that ends up in the daughter cells depends on how they were aligned
17
Q
define genotype
A
- The alleles possessed by an organism
18
Q
Define phenotype
A
- These are the observable features of an organism; it is affected by genes and also the environment
19
Q
Define homozygous
A
- Having 2 identical alleles of a gene
20
Q
Define heterozygous
A
- Having 2 different alleles of a gene
21
Q
Dominant vs Recessive alleles
A
DOMINANT: An allele that has the same effect on the phenotype whether or not another allele is present
RECESSIVE: This allele only affects the phenotype if no dominant allele is present
22
Q
Monohybrid vs dihybrid inheritance
A
MONOHYBRID: Inheritance of 1 gene
DIHYBRID: Inheritance of 2 genes
23
Q
F1 generation Vs F2 generation
A
F1: This is the offspring resulting from the cross between individuals with a homozygous recessive and homozygous dominant
F2: The offspring resulting from a cross between two F1 individuals
24
Q
what is the main difference between the X and Y chromosome
A
- The Y chromosome is shorter and contains fewer genes compared to the X chromosome
25
What is a sex-linked gene
- A gene found on a region of a sex chromosome that is not present on the other sex chromosome
26
define a carrier
- An individual that possesses a particular allele as a single copy whose effect is masked by a dominant allele
27
State the genetic diagram structure for mono and di-hybrid inheritance
1- Parental phenotype
2- Parental genotype
3- Parental gametes
4- Punnett square
5- Ratio
28
What is a test cross
This involves crossing an organism with a dominant genotype/ phenotype with another organism showing a recessive genotype/phenotype
29
define epistasis
- The interaction of 2 genes at different loci; one gene may affect the expression of the other
30
what is an autosomal linkage
- The presence of 2 genes on the same autosome ( any chromosome other than a sex chromosome) so that they are inherited together and do not assort independently
31
state the Chi-squared (X squared) test formula
X squared = SUM (O - E) 2 divided by E
E- expected value
O- Observed value
32
Describe albinism
- The dark pigment is partially or totally missing from the eyes, skin and hair.
- In humans, it results in pale blue or pink irises in the eyes and pale skin.
- The condition is accompanied by poor vision, rapid, jerky movements of the eyes and a tendency to avoid bright light.
33
What is the melanin metabolic pathway
Tyrosine-> DOPA -> Dopaquinone -> Melanin
34
What results in albinism
- The TYR gene is found on the long arm of chromosome 11 and when there is a faulty recessive allele that results in albinism
- the recessive allele of the gene for the enzyme tyrosinase will result in the absence of tyrosinase and therefore tyrosine cannot be converted into DOPA and then dopaquinone
35
Describe sickle cell anaemia and how it caused
- The HBB gene is located in the B-globin polypeptide in chromosome 11.
- Most people have the normal allele however its abnormal form, the base sequence CTT is replaced by CAT due to a mutation.
- When combined with oxygen it does not affect the haemoglobin molecule however when there is a deficit in oxygen, the unusual B-globin is less likely to become soluble
- The red cells stick to each other and form a sickle shape. when this happens the cell becomes useless at transporting oxygen.
- As a result, they will suffer severe anaemia and may die
36
Describe haemophilia and how it occurs
- The F8 gene is found on the X chromosome of the non-homologous region. So it is sex-linked and males only will have 1 copy so cannot mask the effect.
- F8 gene contains the code for synthesising a protein called coagulation factor VIII. This protein plays an important role in the sequence of events during blood clotting.
- Abnormal alleles of this gene result in the production of abnormal forms of VII, less of it or none of it all. This means that blood clotting will not occur normally and excessive bleeding will occur even from a small injury.
37
Describe Huntington's disease and how its causes
- The gene HTT is positioned on chromosome 4 and it codes for the production of a protein called huntingtin. The protein has been found to develop neurones in the brain.
- For some, the nucleotide sequence of this gene contains a large number of repeated CAG triplets. However, the number of repeats is over 40 or between 36-39 (the disease sometimes develops or does not) then neurone development is abnormal and the disease is developed
- This disease is usually developed as a person gets older and they begin to lose their ability to control movement and walking, talking and thinking clearly.
- The faulty allele is dominant and there is a 1in 2 chance that they will inherit this condition from a parent with the allele.
38
Describe the Le gene in stem elongation
- The dominant form of the allele Le allows plants to grow tall but plants that have homozygous recessive allele (lele) then they are short.
They are tall because the dominant allele regulates the synthesis of the last enzyme in a pathway that produces an active form of gibberellin.
- The reason why they are short is because the recessive allele has one nucleotide that differs from the normal allele which codes for alanine instead of threonine at the primary structure of the last enzyme. This makes it non-functional and they do not have active gibberellin.
39
when is a gene said to be expressed
- Once it has been transcribed to mRNA and then mRNA is translated to produce a protein
40
what is an operon
- An operon is a group of genes that are controlled together by the same regulatory system
41
what does the lac operon consist of
- promoter for structural genes
- operator
- structural genes
42
In the Lac operon, what are the 3 structural genes
lacZ: codes for beta-galactosidase
lacY: codes for permease (allows lactose to enter the cell )
lacA: Codes for transacetylase
43
State the sequence of events when there is NO lactose in the medium
- The regulatory gene codes for a protein called a repressor
- The repressor will bind to the operator region, close to the gene for Beta galactosidase
- because the repressor is attached to the operator, RNA polymerase cannot bind to DNA at the promoter region and so no transcription leading to no translation.
44
State the sequence of events that occur when lactose is present in the medium
- Lactose enters the bacterium
- It then binds to the repressor protein, distorting its shape and preventing it from binding to DNA at the operator site.
- Transcription is no longer inhibited and messenger RNA is produced from the 3 structural genes.
- The bacterium can now absorb and break down lactose
45
describe an Inducible enzyme
- This is an enzyme that is only synthesised when its substrate is present e.g B-galactosidase
- The presence of the substrate induces the transcription of the gene for the enzyme
- The binding of the effector molecule (lactose) to the repressor prevents the repressor from binding to the operator, the repressor is released and transcription proceeds.
46
Describe a repressible enzyme
is an enzyme whose synthesis can be inhibited (or repressed) by the presence of a specific molecule, typically the end product of its metabolic pathway.
47
what is a transcription factor
- This is a protein that binds to DNA and affects whether or not a gene is transcribed
48
state 4 examples of the effects of transcription factors
- general transcription factors are necessary for transcription to occur and form part of the protein complex
- A transcription factor is responsible for the determination of sex in mammals
- Many hormones such as testosterone have their effect through transcription factors
- Transcription factors allow responses to environmental stimuli such as switching on the correct genes to respond to high environmental temperatures
49
Describe how gibberellin activates the transcription of the amylase gene.
- PIF is bound to a DELLA protein (Repressor molecule that inhibits transcription)
- Gibberellin bonds with a receptor and an enzyme. This initiates the destruction of the DELLA protein.
- PIF can now bind with the promoter and transcription can be initiated
Biology
flashcards
Decks in class (20)
# Cards
-
Chapter 1- Cells , Microscopy39
-
Chapter 3- Enzymes31
-
Chapter 2-Biological molecules63
-
Chapter 4- Cell Membrane48
-
Chapter 5- Mitotic cell cycle28
-
Chapter 6- Nucleic Acid37
-
Chapter 7- Transport in plants25
-
Chapter 8- Transport in Mammals56
-
Chapter 9-Gas exchange24
-
Chapter 10-Infectious diseases37
-
Chapter 11- Immunity45
-
Paper 3- Practical18
-
Chapter 12- Energy and Respiration30
-
Chapter 13- Photosynthesis20
-
Chapter 14- Homeostasis52
-
Chapter 15- Control and Coordination44
-
Chapter 16- Inheritance49
-
Chapter 17- Selection and Evolution37
-
Chapter 18- Classification, biodiversity and conservation44
-
Chapter 19- Genetic Technology52
