Chapter 9-11 Flashcards
Genetic counselling
provision of expert advice to prospective and actual parents about risks of occurrence or recurrence of inherited disorders
Genes determine our…
characteristics (phenotypes)
Genes are passed on from…
generation to generation
In our body we have how many sets of genes
double set, one from mother, one from father
Gamete
a haploid cell, that is able to unite with a gamete of the opposite sex to form a zygote
Haploid
a cell that has one copy of each specific chromosome
Cell cycle
is a set of events that occur cyclically that lead to the repeated replication of the eukaryotic cell
Cell cycle phases
G0 (resting), G1 (growth 1), S (synthesis), G2 (growth 2), M (mitosis/meiosis + cytokinesis)
What happens in S
DNA is duplicated as a result of the chromosomes duplicating
Important thing about cell cycle
only dividing cells are in the cell cycle, others are in G0
Meiosis
process of nuclear division that results in the production of new haploid cells
Mitosis
the process of nuclear division resulting in giving rise to two identical daughter cells.
Binary fission (where, results in, asexual or sexual)
where: prokaryotic cells
results in: exact copies of the cells (assuming there are no mutations)
is it asexual/sexual: asexual
Binary fission process
- DNA replication occurs, the single circular chromosomes relocates into two circular chromosomes (Presumably plasmids and ribosomes replicate)
- the twin chromosomes attach to opposite poles of the cell membrane
the cell begins to elongate, dragging the chromosomes to opposite ends - the cell membrane and walk invaginated upon itself
- the parent cell splits into two daughter cells as the cell membrane and wall separates the two new parent cells
Sexual cell reproduction involves
the fusion of gametes
Regulator genes
genes that produce proteins that control the action of other genes and these actions determine whether other genes are active (‘on’) or not (‘off’) and, if active, the rate at which their products are made.
Two ways that regulator gene proteins can act
DNA-binding proteins, signalling proteins
DNA-binding proteins
bind to regions of nuclear DNA near genes and directly switch these genes on or off (net positive charge)
Signalling proteins
bind to receptors on the membrane of cells in their target tissue and trigger a series of intercellular reactions that switch genes on or off
Human genome project
international project directed at the identification of the sequence of the more than three billion bases in the human genome.
Aim of human genome project
store the sequences in a data base to create a map of all the human genes.
Results caused by human genome project (5)
insights into diagnosis, treatment, prevention, human biology, evolution
The nature of genetic code
the genetic code consists of triplet base sequences, code is non-overlapping (e.g. 12 bases = only 4 triplets), said to be universal (virtually same in plants/animals/bacteria), is redundant (more than one triplet codes for same thing), information encoded in DNA is instructions to assemble polypeptides from amino acids, includes start and stop codons
Start codon
TAC
Number of stop codons
3
Stop codons
ATT, ATC, ACT
Genetic code
non-overlapping triplet code consisting of groups of three bases. The sequence of nucleotides, coded in triplets (codons) along the mRNA, which determines the sequence of amino acids in protein synthesis.
DNA sequence definition
relative order of base pairs, whether in a fragment of DNA, a gene, chromosome or an entire genome.
Gene
the fundamental physical and functional unit of heredity made of DNA. A gene is an ordered sequence of nucleotides located in a particular position on a particular chromosome that encodes a specific functional product
Gene expression
The process by which a gene’s coded information is converted into the structures present and operating in the cell. Expressed genes include those that are transcribed into mRNA and then translated into protein and those that are transcribed into RNA but not translated into protein (e.g., transfer and ribosomal RNAs).
Introns
The DNA base sequences interrupting the protein-coding sequences of a gene; these sequences are transcribed into RNA but are cut out of the message before it is translated into protein.
Exons
The protein-coding DNA sequences of a gene
Transcription
The synthesis of an RNA copy from a sequence of DNA (a gene); the first step in gene expression.
Translation
The process in which the genetic code carried by mRNA directs the synthesis of proteins from amino acids.
tRNA
A class of RNA having structures with triplet nucleotide sequences that are complementary to the triplet nucleotide coding sequences of mRNA.
Role of tRNA
to bond with amino acids and transfer them to the ribosomes, where proteins are assembled according to the genetic code carried by mRNA.
Promoter
a site on DNA to which RNA polymerase will bind and initiate transcription.
Polymerase (DNA/RNA)
Enzymes that catalyse the synthesis of nucleic acids on preexisting nucleic acid templates, assembling RNA from ribonucleotides or DNA from deoxyribonucleotides.
Primer
Short preexisting polynucleotide chain to which new deoxyribonucleotides can be added by DNA polymerase.
DNA replication
The use of existing DNA as a template for the synthesis of new DNA strands. In humans and other eukaryotes, replication occurs in the cell nucleus.
Karyotypes
graphic display of the complete set of chromosomes from a cell of a particular organism.
Ideogram
stylised representation of a haploid set of chromosomes arranged in order of decreasing size.
Autosomal chromosomes
homologous pairs that does not differ between the sexes
Autosomes can be distinguished by (3)
relative size, position on centromere, patterns of light and dark bands with special staining techniques
Sex chromosomes
determine the sex of the organism
Somatic cells (colloquial)
body cells
Mitosis
nuclear division of a somatic cell resulting in two identical daughter cells
Stages of Mitosis
(I) PMAT
Stages of Meiosis
(interphase i), prophase i, metaphase i, anaphase i, telophase i, cytokinesis i, prophase ii, metaphase ii, anaphase ii, telophase ii, cytokinesis ii
Interphase
G1, S, G2
Prophase
chromatin shortens and thickens into small compact chromosomes, spindle forms the centrosomes around the nucleus and approaches the nucleus, nuclear membrane breaks down
Metaphase
chromosomes align in a plane along the middle of the nucleus, the spindle attaches to the centromeres of the chromosome
Anaphase
spindle contracts, separating each double stranded chromosome into two single stranded chromosomes, and the single stranded chromosomes migrate to opposite poles of the cell, attached to the spindle
Telophase
the chromosomes uncoil and become less compact (decondense), two nuclear membranes reform
Cytokinesis
cytoplasm splits to identical daughter cells
When does crossing over occur
occurs in prophase i of meiosis
Aneuploidy
not the right number of chromosomes
Polyploidy
whole set of chromosomes fail to disjunct
Congenital disorders caused by…
mistakes in chromosome numbers and chromosomes abnormalities
Non-disjunction definition
when an error occurs in separation of chromosomes
Non-disjunction in 1st stage affects…
all 4 cells
Non-disjunction in 2nd stage affects…
2 only
Gonads
organs where gametes are formed
Germline cells
cells that give rise to gametes
How is zygote formed
nucleus of sperm fuses to nucleus of egg
What are the only cells to cross the genetic gap
gametes; all other cells die when the cell dies
Somatic cells definition
cells of the body that are diploid
How is DNA transmitted across generations
through gametes
Chromosomes
thread-like structures composed of DNA and protein
Chromosomes are only visible (under a microscope) during…
meiosis and mitosis
Chromosome map
drawing of a chromosome showing the gene loci
Structure of chromosome
- has a centromere in the centre of the chromosomes
- kinetochore
- has a telomere at ends
The centromere has ….
constriction
Kinetochore (3)
surrounds the centromere, made of protein, forms the attachment points for spindle fibres necessary for movement
Telomere
DNA made up of thousands of repeats of sequences of base pairs
Telomere role - prevent chromosomes sticking together and they enable complete replication of chromosomes to occur.
Human telomere sequence
TTAGGG
Chromatids
two strands replicated chromosome which are joined together by a single centromere
Centromere
constricted part of the chromosome that contains the region where spindle fibres attach during meiosis and mitosis.
Loci/locus
the position of a gene on a chromosome
Linked genes are
on the same chromosome
Linkage groups are
refers to chromosomes, usually equal to haploid number of chromosomes.
Homologous chromosomes
a pair of chromosomes containing the same linear gene sequences, each derived from one parent. (but different alleles)
The larger the chromosome…
the more genes located on it
Chromosome mutations
include gross structural alterations of chromosomes, changes in numbers of chromosomes
Gross structural alterations of chromosomes
includes translocation, inversions, duplication/deletion of sections of the chromosome
Translocation
a section of one chromosome attaches to the end of another chromosome.
Inversions
single chromosome undergoes breakage and a segment of the chromosome is reversed end to end (do not cause abnormalities in carriers as long as it is balanced with no extra/missing info)
Changes in number or chromosomes is caused by
non-disjunction
Non-disjunction causes…
aneuploidy and polyploidy organisms
Aneuploidy
abnormal number of chromosomes
Examples of aneuploidy
abnormal number of chromosomes
Polyploidy
whole sets of chromosomes do not separate during meiosis
Karyotypes
graphic display of the complete set of chromosomes from a cell of a particular organism.
Autosomal chromosomes
homologous pairs that does not differ between the sexes
Genome
the full set of genes of an individual
Alleles
alternative forms/variants of a particular gene that controls one function
Genotype
refers to both the double set of genetic instructions present in a diploid organism and to the genetic makeup of an organism at one particular gene locus
Phenotype
expression of an organism’s genotype in its structural, biochemical and physiological characteristics
Heterozygote
the presence of different alleles at one or more loci on homologous chromosomes
Homozygote
an individual with both identical alleles (versions of a single gene) at one locus (position).
Polygenes
many genes that work together to produce a trait.
Polygenes cause… (type of variation)
continuous variation
Continuous variation
results in characteristics which exhibit a continuos range of traits (phenotypes) across a population.
Examples of continuous variation
height, skin colour, eye colour.
Discontinuous variation
in a population occurs when members of a population can be grouped into a few discrete and non-overlapping classes with regard to expression of a trait
Example of discontinuous variation
number of fingers
Monomorphic population
all members have identical phenotypic trait
Polymorphic population
members have several variants of particular trait
Mutation
permanent change in the genetic material (or DNA sequence).
Important to remember about mutation
spontaneous events
Environment effect of genes can be either..
either internal or external
Examples of environment effect on genes (2)
chemicals in external environment cause birth defects/alter appearance, absence of chemical in body - trait not expressed e.t.c.
Test cross
a cross between an organism of interest (that exhibits the dominant trait) and an organism with a known recessive phenotype, in order to determine the genotype of a particular trait in the organism of interest, or if two genes are linked.
Pedigree
a “family tree” that shows the frequency and occurrence of particular phenotypes (hence alleles) over many generations
Symbol for male
square
Symbol for female
circle
Symbol for twins identical vs fraternal
identical has line through middle, fraternal has no line
Identify if recessive
skips generation, both parents have it then all children have it
Identify if sex-linked dominant pedigree
father = all daughters, if a son = mother must have
Identify if sex-linked recessive
father has = all daughter, mother has = all sons
Sex-linked trait
an allele (gene) that is found on the sex chromosomes (usually X)
Hemizygous
for sex-linked trait: carrier, normal, affected
Important to note for sex-linked phenotype
List gender + phenotype
Lethal allele
the homozygous genotype is lethal
How to know if gene is linked or not
if phenotypic ratio varies from the expected, it is linked
Down’s syndrome
extra copy of the 21 chromosome
WZ/ZZ in what animals
some birds, some snakes (tiger), monitor lizards (goannas), amphibians (frog),
Egg production in females called
Oögenesis
Oögenesis how many eggs produced each stage
two then only one, two then only one
Sperm production in males called
Spermatogenesis
Spermatogenesis how many eggs produced in each stage
2, so four in total at end
Asexual reproduction
production of genetically identical offspring from one parental organism only.
Sexual reproduction
method of producing offspring that involves a genetic contribution (usually) from two parents, typically the fusion of a haploid egg and a haploid sperm to form a diploid zygote.
Recombination
process of generating new combinations of alleles of various genes both by crossing over and by independent assortment during meiosis.
Number of genes in each cell
21,000
Mitochondrial genes
genes located in the DNA of mitochondria and transmitted in a matrilineal manner
Multiple alleles
refers to three or more alleles of a specific gene
Heterozygous
a cell/organism whose genotype for a particular gene comprises two different alleles
Homozygous
cell/organism whose genotype for a particular gene comprises of two identical alleles
Dominant
refers to a trait that is expressed in the heterozygous condition
Recessive
refers to a trait that is only expressed in the homozygous form i.e. is not expressed in the heterozygous form.
Sex-linked trait
refers to a trait which is controlled by a gene with its locus on a sex-chromosome
Two types of sex-linked traits
x linked and y linked
How to find out which trait is dominant
the phenotype of the heterzygote
X-inactivation
random switching off of one gene of the two X-chromosomes present in somatic cells of mammalian females
When does x-inactivation occur
during early embryonic development.
Carrier
heterzygote that has the allele for the recessive trait but does not express the trait
Co-dominance
relationship between two alleles of a gene, where the alleles are equally dominant, such that a heterozygous organism shows the expression of both alleles in its phenotype.
Difference between co-dominance and incomplete dominance red/white flower
co-dominance would be red and white dots, incomplete dominance is pink flower
The genotype + environment forms
the phenotype
Why test crosses are used
to identify if organism showing a dominant trait is homozygous or heterozygous, establish linkage relationships
To work out if a trait is dominant homozygous minimum organisms to be born
16
Ways linked genes are represented
A b () a B, Ab/aB, A b (=) a B
Test to work out if gene is linked
cross two heterozygotes
If the gene is linked for heterozygous test, the ratio will be
9:3:3:1
If it is not linked, the ratio for heterozygous test will be
1:1:1:1
Gene assortment
independent distribution of unlinked genes to gametes as a result of the independent movement of non-homologous chromosomes carrying those genes to opposite poles during meiosis.
Distance between loci formula
100*number of recombinant offspring/total number of offspring
What did Mendel study
inheritance of variation in the traits
What lead to Mendel’s success
one trait at a time, known history of parents, recording parentage, counting offspring
What do large numbers of offspring allow (3)
egularities to be recognised and valid averages to be identified, to ‘ascertain their statistical relations’
Mendel’s discoveries (7)
each trait controlled by a pair of inherited factors (alleles). For each trait individual plants had two factors that could be identical or different, plants with identical factors were referred to as pure breeding and plants with different factors were called hybrids. Each factor was a discrete particle and retained its identity across generations. Recessive and Dominant. One factor per gamete. Genes behaved independently. The results were the same regardless of plant was used as male/female.
Transforming factor
substance that had the ability to change the genetic character of bacteria that was later identified as being DNA?
Dissociation
separation of double-stranded DNA molecule into its single strands, which occurs when the hydrogen bonds stabilising the two strands are broken.
Re-association
re-pairing of single strands of DNA during cooling after the two strands of a DNA double helix have been dissociated by heating.
Hybridisation
pairing between single-stranded complementary DNA segments from organisms from the same or even different species.
Genome
the full set of genes carried by an individual (or cell)
Gene sequencing
identification of the order or sequence of bases along the DNA of a specific gene
Decoded
refers to the translation of genetic information held in DNA into amino acids
Encoded
refers to the holding of genetic information in DNA in coded form as a base sequence.
Genomics
study of genomes
Proteome
full set of proteins produced by a single cell or organism
Single nucleotide polymorphism
when one base sequence varies.
Opening reading frames
reading frames (codes) that can be transcribed
Name of genes that result in proteins
protein-encoding genes
Gene duplication
where a second copy if the DNA sequence of a gene appears in a genome.
Gene action
processes of transcription and translation of a gene into a gene product.
Transcription steps
- RNA polymerase attaches to a specific promotor sequence of DNA in the upstream region of the template strand. The double-stranded DNA of the strand unwinds and exposes the bases of the template strand.
- The base sequence of the DNA template guides the building of a complementary copy of the mRNA sequence. The RNA polymers enzyme moves along the DNA template in a 3’ to 5’ direction and, as it moves, complementary nucleotides are brought into place, and, one by one, are mined to form an RNA chain.
- After the RNA polymerase moves past the coding region and into the down-stream region of the gene, transcription stops and the mRNA molecule is released from the template. The result of this process is a single stranded molecule of pre mRNA.
What happens after transcription
pre-mRNA is modified into mRNA
What is modification of pre-mRNA called
post-transcription modification
What happens in post-transcription modification
introns are cut out, poly-A tail added to 3’ end and a methyl cap is added to 3’ end
How are introns spliced
spliceosomes
Where does translation occur
ribosomes (cytoplasm)
How are amino acids bought to mRNA
tRNA
tRNA structure
tRNA consists of a strand of 76 nucleotides coiled and pairs with themselves. At one end of the tRNA molecule there are three bases that make up an anticodon, at the other end is a region that attaches to one specific amino acid
What does amino acyl tRNA synthetase do
catalyses the linking of each amino acid to its specific tRNA carrier.
Codon
sequences of 3 bases
DNA is a… model
semi-conservative model
Some genes are active only
in specific tissues
Pre mRNA also known as
primary transcript
Two steps in gene expression
transcription, translation
RNA polymerase role
unwind DNA and synthesise an RNA strand complementary to the 3’-5’ direction of the gene
G1 phase
cell grows in size, duplicating its organelles, synthesised proteins required for S phase
G2 phase
grows in size again, and synthesising proteins for M
M
mitosis/meiosis
DNA replication
- DNA helicase unwinds DNA
- primer is synthesised by RNA/DNA primes
- DNA polymerase synthesises a new DNA strand starting from the primers (5’-3’) small segments backwards (Okazaki fragments)
- leading strand? lagging strand?
- DNA ligase join fragments in each strand to form DNA strand
Silent mutations
no change in amino acid sequences
Missense mutations
replacement of one amino acid with another
Nonsense mutations
mutated into a stop codon
Gene amplifications
segments of DNA are repeated again
Prophase 1
chromatin shortens and thickens into small and compact chromosomes, the spindle forms the centrosomes around the cycles and approaches the nucleus, the chromosomes line up in their homologous chromosomes and cross over, the nuclear membrane breaks down
Metaphase 1
spindle fibres attach to the centromeres of each homologous chromosome, the tetrads line up in a plane in the middle of the cell
Anaphase 1
the spindle contracts, separating each tetrad back into the double stranded chromosomes, and the double stranded chromosomes migrate to opposite poles of the cell attached to the spindle
Telophase 1
chromosomes uncoil and become less compact, two nuclear membranes reform,
Meiosis 2 stages are the same as…
mitosis 1 stages
Identical twins are also known as
monozygotic twins
Genotypic ratio
expected ratio of offspring with each possible genotype
Phenotypic ratio
expected ratio off offspring with each possible phenotype
Difference between prokaryote and eukaryotes chromosomes
Prokaryotes are circular, eukaryotes are linear
Prokaryotes don’t have introns
Prokaryotes lack histones
