MGD Session 4 Inheritance of Genes Flashcards
What enzymes are involved in the process of DNA replication?
DNA polymerase, DNA helicase and primase
What reaction does DNA polymerase catalyse, and give description of main reactants and products
Name four dNTPs
DNA polymerase catalyses the reaction (dNMP)n + dNTP (dNMP)n+1 + PPi
(dNMP)n = DNA chain, n number of nucleotide
dNTP = any or all nucleotides, represented by N
PPi = Inorganic phosphate released
deoxyadenosine triphosphate (dATP), deoxyguanosine triphosphate (dGTP), deoxycytidine triphosphate (dCTP), deoxythymidine triphosphate (dTTP)
What provides the energy for the DNA polymerase reaction?
reaction driven by phosphate hydrolysis. Two phsophates lost from dNTP, which provides energy for polymerisation.
What are the three steps of DNA replication?
Initiation, Elongation and Termination
What occurs in the first step of DNA replication?
Point of origin determined, which differs depending on sequence.
Helicase unravels the DNA double helix
Primase adds primer to leading strand – kick starts reaction
Why is primase necessary to start the DNA polymerase chain reaction?
because DNA polymerase can only extend from 3’ ends of pre-existing chains to 5’
Why can DNA polymerase only extend from 3’-5’ and not vice versa?
Because of the shape of its active site
What group is attached to the 5’ carbon in a nucleotide?
Phosphate, 3’ is OH
What occurs in elongation?
Leading strand is replicated from 5’ –> 3’ as normal. However the lagging strand is replicated discontinuously in Okazaki fragments. These fragments are then joined by DNA ligase from OH group to Phosphate group covalently.
Why are Okazaki fragments formed?
DNA polymerase only works in 5’-3’ direction. Has to go “backwards” when forming lag strand, so discontinuous. Polymerase works a little bit at a time, moving to different sections once helicase opened up more DNA. insufficent time for continous replication on lag strand, so discontinuous,
What are the four sections of cell division?
G1 (cell growth), Synthesis (DNA replication), G2 (production of proteins necesary for division) and Mitosis
How many mitotic rounds during development?
50
What type of cells divide by mitosis?
Somatic
Where is the checkpoint in the cell cycle? What is its purpose?
Also, what happens in G1
At the start of g1, goes to g0 and causes cell cycle arrest.
Cellular contents, exculding the chromosomes, are duplicated
What must a cell do before it can physically divide?
Duplicate each of the 46 chromosomes during S phase
What is formed when a chromosone divides?
two identical sister chromatids that are touching in a structure called the centromere.
At what stage in cell cycle is DNA duplication checked and repaired?
G2
What happens in prophase?
Chromosones condense
Nuclear membrane disappearing
Spindle fibres appear
What happens in prometaphase?
Spindle fibres attach to chromosones
Chromosones condense
What happens in metaphase?
Chromosones align
What happens in Anaphase?
Centromeres divide
Sister chromatids move to opposite poles
What happens in Telophase?
Cleavage occurs
Nuclear membrane reforms
Chromosones condense
Spindle fibres disappear
What are the two types of meiosis?
Spermatogeneis and Oogenesis
How does meiosis create genetic diversity?
independent assortment of chromosomes (during meiosis I) and crossing-over.
How does the process of meiosis differ from the process of mitosis?
In meiosis I, rather than the chromosomes lining up along the equator and the chromatids splitting apart like in mitosis, the chromosomes (duplicated from S phase) line up with their homologous pairs. This is when crossing over occurs:
How many chromosomes in a gamete?
n (2n being standard), so known as haploid.
What is the length of spermatogenesis?
48 days
What is the length of oogenesis?
12-50 years
Define genotype
The genetic make-up of an individual (either as a whole or one specific genetic locus)
Define phenotype
All observable characteristics of an individual or the expressed trait as a result of the genetic make-up of one (or more) specific genetic locus (loci).
Give five environmental factors which affect both phenotype and genotype
Radiation Mutagens Chemicals that can affect cell growth Diet Life-style
Define gene
A unit of heredity; a length of DNA on a chromosome that contains the code for a protein
Define allele
An alternative form of a gene; each individual has two alleles for every gene, which can either be the same or different. Many different alleles in population.
What is autosomal inheritance?
When the gene in question is located on an autosome (not a sex chromosome)
What is the usual type of genotype for autosomal dominant person?
Heterozygous, rarely found in homozygous state as aborts fetus.
Name a genetic disease which is autosomal dominant
Familial hypercholesterolemia
If two heterozygote carriers of an autosomal recessive allele have a child, what is the chance it will be affected?
25%
Name a genetic disease which is autosomal recessive
Cystic fibrosis, Albinism
What is sex linked inheritance?
When the gene in question is located on a sex chromosome
Give example of x-linked recessive disease
Haemophilla, Duchenne muscular dystrophy
What is Y linked inheritance?
when the gene in question is located on the Y-chromosome and inherited directly from father to son.
Homozygous
two alleles of a gene are the same
Heterozygous
two alleles of a gene are different
Hemizygous
Only one allele of a gene on the X chromosone (males only)
Dominance
A phenotypic trait is dominant when it occurs in both homo and heterozygotes.
Recessive
A phenotypic trait is recessive when it occurs only in homozygotes.
Co-dominance
When both alleles are expressed in the phenotype of heterozygotes
E.g. AB Blood type
Complementation
More than one gene is responsible for phenotype.
Therefore a child of two recessive parents can be unaffected if parents have different defective genes (inherits healthy genes)
E.g. Albinism
Three enzymes responsible for expression of trait
What are linked genes?
Two genes close together on the same chromosome, will not show independent assortment.
How can linked alleles be separated during mitosis?
By the process of crossing over and recombination
What is recombination frequency dependent on?
distance between genes.
Genes close together are…
tightly linked
What does 1 map unit equal?
1% recombination
When is genetic mapping more accurate?
When genes are close together
