C- Topic 3 Flashcards
Which methods enable cells to be controlled for pre-natal diagnosis of chromosomal abnormalities?
- Chorionic villus sampling
2. Amniocentesis
What are plasmids?
Small loops of naked DNA
That can be passed from 1 bacteria to another via the pilli
This is how antibiotic resistance occurs
Where can plasmids be found?
Présent in most prokaryotes
Eukaryotes do not have plasmids
What are karyograms used for?
To determine sex and to diagnose conditions caused by chromosomal abnormalities
What is genotype?
The combination of all the alleles in an organism
Define phenotype
The characteristics of an organism determined by their genotype
Define dominant alleles
The phenotype observed is the same when present in a homozygous or heterozygous state
Define recessive allele
It’s presence masked by a dominant allele. The phenotype of a recessive allele is only observed in a homologous state
Define homozygous
Both alleles of the gene are the same
Define heterozygous
Both alleles of the gene are different
What is a genetic disease?
A genetic disease is caused by a gene mutation
What are sex linked genes?
Sex linked genes are those present on the sex chromosomes
Thé X chromosome is much larger so some are only located on the X chromosome
Therefore only males have only allele of these genes
Only females can be heterozygous
Due to this, the pattern of inheritance of sex-linked genes is different in males and females
What are 2 examples of sex linked diseases?
Haemophilia
Colorblindness
Diploid cells contain two (1) of each gene because chromosomes are present in (2) pairs. During the process of meiosis, the two alleles of each gene become separated into different (3). Gametes are (4); they only contain (5) allele of each gene. If a homologous cell undergoes meiosis, the four gametes will be (6). If a heterozygous cell undergoes meiosis, (7) gametes will contain the dominant allele and (8) will contain the recessive allele.
1 - alleles 2- homologous 3 - gametes 4 - haploid 5 - one 6 - same 7 - half 8 - half
Outline the human genome project
- The order of base pairs in DNA fragments can be determined by a technique called DNA sequencing
- Improvements in sequencing technology allowed more DNA sequence to be determined faster & cheaper
- Bioformatics software was also developed to join overlapping fragments of DNA sequence together
- an ambitious project to sequence the entire human genomes started in the 1990’s
- the project included collaboration between scientists from several countries & it was completed in 2003
- the human genome compromises about 3.2 billion base pairs
- further improvements in sequencing speed and reduced costs, have enabled the genomes of thousands of other organisms to be sequenced
Which other factor promotes genetic variation in organisms that have a sexual life cycle?
random fertilisation
Most species of eukaryotic organisms have a number of (1) chromosomes. For example, humans have (2) different chromosomes. The different chromosomes contain different (3).
1 - different
2 - 23
3 - genes
What is the relationship between a mothers age and the chances of having a child w Down syndrome?
- as a mothers age increases, so does the chance of having a child w down syndrome
- there is very little risk up to 30 years old
What is sickle cell anaemia an example of?
Sickle cell anaemia is an example of a disease caused by a single base substitution mutation
Why is the sickle cell shape a major implication?
- sickle cells may form clots within the capillaries, blocking blood supply to vital organs and causing myriad health issues
- sickle cells are also destroyed more rapidly than normal cells, leading to a low red blood cell count (anaemia)
Gene definition
a heritable factor that controls or influences a specific characteristic, consisting of a length of DNA occupying a particular position on a chromosome (locus)
Alleles definition
different forms of a specific gene
Gene locus definition
specific position of a gene on a chromosome
- alleles of a gene are found at the same locus but have different DNA base sequences
Do all members of a species have the same number of chromosomes?
Yes
all members of a species have the same number of chromosomes - each w the same number of genes in the same loci
Number of genes vary between species
What is a genome?
- the entire genetic material of an organism
- consists of DNA, RNA or RNA viruses & includes both the genes & the non-coding sequences
What type of mutation is sickle cell disease?
a single base-substitution mutation
what causes sickle cell disease?
a single base-substitution, a change to the base sequence of mRNA transcribed from it & a change to the sequence of a polypeptide in haemoglobin
what is a gene mutation?
a permanent change in the base sequence of DNA
Do all mutations cause disease?
No, but some do
What is a genetic disease?
When a gene is wrongly expressed
What is base-substitution mutation?
when 1 base is substituted for another
- this may or may not or may not result in the change of a single amino acid in the polypeptide
What is a silent mutation?
the change in base has no effect on the amino acid produced
What is a missense mutation?
change in base sequence has caused 1 different amino acid to be produced
What is a non-sense mutation?
the change in base sequence that has caused a STOP codon to be produced, so the polypeptide produced is shortened
- e.g cystic fibrosis
What is malaria?
- a parasitic disease caused by a plasmodium cell
- it is carried by mosquitos & invades normal red blood cells
Where is sickle cell disease more prevalent?
where malaria is endemic
When does natural selection occur?
when there is variation within a species(as a result of a mutation)
- if individual is benefitted by the mutation, it has greater reproductive success, thus passing on the mutation
difference of karyotype and karyogram
A karyogram is A diagram or photograph of the chromosomes present in a nucleus (of a eukaryote cell) arranged in homologous pairs of decreasing length
A karyotype is A property of the cell described by the number and type of chromosomes present in the nucleus (of a eukaryote cell)
Explain why meiosis is described as a reduction division.
because it reduces the number of chromosomes from 46 chromosomes or 2n to 23 chromosomes or n (n describes a single chromosome set).
Disjunction
the separation of homologous pairs of chromosomes following meiotic synapsis
What are the 2 types of DNA that prokaryotes have?
- single chromosome
- plasmids
When is the copy of the chromosome made in prokaryotes?
before binary fission
Who is John Carin?
the dude who produced images of DNA molecules from E.coli by autoradiography
How are nucleosomes formed?
by the wrapping of DNA around histone proteins
How many pairs of chromosomes do humans have?
23 pairs
How can chromosomes vary?
by length
- the number of base pairs in the DNA molecule
by position of the centromere
location
- genes occur at a specific locus, it is always found at the same position on the same chromosome
- locus & genes possessed vary between species
Is chromosome number an important characteristic of a species?
Yes
- organisms w different numbers of chromosomes are unlikely to interbreed successfully
- reflects the complexity of an organism
- chromosome number -> N number
Which type of nuclei are less susceptible to diseases?
Diploid nuclei
Why are diploid nuclei less susceptible to diseases?
bc they have 2 copies of a gene, which means the organisms is more likely to possess at least 1 healthy copy
What is a zygote?
a fertilised egg cell
What type of nuclei do gametes have?
haploid nuclei
What is the diploid number of chromosomes in each human cell?
46
What is the haploid number of chromosomes in each human cell?
23
How many diploid chromosomes in Oryza sativa (asian rice)?
24
How many diploid chromosomes in Parascaris equoru (roundworm)?
2
How many diploid chromosomes in Canis familiarise (dog)?
78
How many diploid chromosomes in pan troglodytes (gorilla)?
48
are somatic cell nuclei haploid or diploid?
diploid (2n)
what do somatic have?
homologous pair of each chromosomes
- 1 pair is parental - inherited from the father
- 1 is maternal - inherited from the mother
