MGD Session 4 Flashcards
What are the five stages of the cell cycle?
G1 (Prepatation for Replication) S (DNA Replication) G2 (Preparation for Division) Mitosis (Division of the cell) Cytokinesis (Division of the cytoplasm)
What enzyme catalyses DNA replication?
DNA Polymerase
What reaction exactly does DNA polymerase catalyse?
(dNMP)n + dNTP –> (dNMP)n+1 + PPi
In which direction is chain growth of a DNA strand?
5’ to 3’
What are the three stages of DNA replication in both eukaryotes and prokaryotes?
Initiation, Elongation, Termination
Explain the initiation stage of DNA replication.
The origin of replication is recognised. Helicase unravels the DNA double helix and specific proteins are required to interact with the DNA and the polymerase. Primase is required to initiate the replication.
Why is primase required?
Because polymerase can only extend from a 3’ end, it cannot create a new strand
Explain the elongation stage of DNA replication
The leading strand is replicated from 5’ to 3’. The lagging strand is replicated discontinuously in fragments which are then joined.
What joins the fragments together?
DNA Ligase (from OH group to phosphate group)
What is the name of the fragments created by replication of the lagging strand?
Okazaki fragments
Explain the termination stage of DNA replication.
Replication takes place from both ends of the DNA strands. Therefore there are two leading strands and two lagging strands. When they meet, DNA ligase joins the end of the leading strand to the start of the lagging strand.
What does semi conservative replication mean?
That one strand of the parent DNA is conserved in each daughter cell when replication takes place.
What is meant by metacentric?
The centromere is in the centre of the chromosome
What is meant by submetacentric?
The centromere is just higher or lower than the centre of the chromosome
What is meant by acrocentric?
The centromere is close to the end of the chromosome
What is meant by telocentric?
The centromere is at the end of the chromosome (not present in humans)
Name the four kinds of dNTP.
dATP, dCTP, dTTP and dGTP
How many mitotic rounds take place during development?
Approximately 50
What does DNA helicase do?
With the energy from ATP it unwinds the DNA helix to allow DNA replication.
List the 5 stages of mitosis.
Prophase Prometaphase Metaphase Anaphase Telophase
What is a haploid cell?
A cell that only contains one set of 23 chromosomes. i.e. human gametes
Explain the difference between mitosis and meiosis.
In mitosis, the cell undergoes one round of replication and one round of division. In meiosis, the cell undergoes one round of replication and two rounds of division.
What happens in prophase?
Chromosomes condense
What happens in prometaphase?
hromosomes condense and spindle fibres attach to chromosomes
What happens in metaphase?
Chromosomes align
What happens in anaphase?
Centromeres divide and sister chromatids move to opposite poles.
What happens in telophase?
Spindle fibres disappear, nuclear membrane reforms and chromosomes condense.
What happens in cytokinesis?
Cytoplasm divides
How does meiosis generate genetic diversity? (2 ways)
Independent assortment of chromosomes
Crossing-over
In spermatogenesis, how many sperms are produced from one spermatogonium?
4 sperms.
How long does spermatogenesis take?
Roughly 48 days
In oogenesis, how many eggs are produced from one oogonium?
1 egg and 3 polar bodies
How long does oogenesis take?
12-50 years
When does crossing over occur?
In meiosis I when the homologous chromosomes are divided.
What is a genotype?
The genetic makeup of an individual
What is a phenotype?
All observable characteristic of an individual or the expressed trait as a result of the genetic makeup.
What 5 environmental factors can have an influence on the genotype/phenotype?
Radiation Mutagens Chemicals that affect cell growth Diet Lifestyle
What is a gene?
A unit of heredity, a length of DNA on a chromosome that contains the code for a protein.
What is an allele?
An alternative form of a gene. Each individual has two alleles for every gene which can be the same or different.
What does homozygous mean?
The two alleles of a gene are the same
What does heterozygous mean?
Two alleles of a gene are different
What does hemizygous mean?
There is only one allele of the gene (i.e. the X chromosome in males)
Define autosomal dominant and give an example of an autosomal dominant condition.
When the gene is located on an autosome and you only have to be heterozygous to be affected. Usually affects someone in every generation. e.g. Marfan’s
Define autosomal recessive and give an example of an autosomal recessive condition.
Where the gene is located on an autosome but you have to be homozygous for the diseased allele to be affected e.g. cystic fibrosis
What is sex-linked inheritance?
Where the gene is located on a sex chromosome (X or Y)
What is dominance?
When the trait occurs in homo and heterozygotes.
What is meant by a ‘recessive’ allele?
Where the allele has to be present in homozygous form to be present in the phenotype.
What is codominance?
Where both alleles are expressed in the phenotype.
What is complementation?
When more than one gene is responsible for the phenotype.
What is linkage?
When genes are close together on the same chromosome.
How can two linked alleles be separated during meiosis?
Via crossing over and recombination
How are the following types of people represented on a pedigree diagram?
a) normal male
b) affected male
c) normal female
d) affected female
a) White square
b) Shaded square
c) White circle
d) Shaded circle
How are the following types of people represented on a pedigree diagram?
a) carrier male
b) carrier female
c) person of unknown sex
d) deceased male/female
a) half shaded square or square with a dot
b) half shaded circle or circle with a dot
c) diamond
d) square / circle with a diagonal line through
What is a genetic map?
The arrangement and distance between genes on a chromosome deduced from studies of recombination
When genes are closer together on a chromosome, is recombination more or less likely?
Less likely
How do you calculate recombination frequency?
Divide the number of recombinant offspring by the number of offspring equal or lower down on the pedigree diagram who’s genotypes we are sure about.
