Genetics
IB Biology Genetics
IB Biology Genetics
Kartei Details
| Karten | 50 |
|---|---|
| Sprache | English |
| Kategorie | Biologie |
| Stufe | Andere |
| Erstellt / Aktualisiert | 11.03.2013 / 18.05.2018 |
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What are eukaryote chromosomes made of?
DNA and Proteins
What are the chromosome facts?
1. The number of chromosomes per species is fixed
2. The shape of a chromosome is characteristic
3. The chromosomes of a cell occur in homologous pairs
4. Chromosomes hold the hereditary factors - genes
5. Chromosomes copy themselves
What is a gene?
A heritable factor that controls a specific characteristic
What is an allele?
One specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene
What is a genome?
The whole of the genetic information of an organism
What is a homologous chromosome?
Chromosomes that occur in diploid cells, comtaining the same sequence of genes, but have come from different parents
What is a sister chromatid?
During interphase the DNA is replicated so a chromosome will have two identical sister chromatids when it enters cell division
How do mutations occur, and how can the chance of occurrence be increased?
Mutations occur randomly, but the chance of occurrance can be increased by mutagens e.g. radiation, uv light and poisons
What do mutations affect?
Transcription and translation
List two common mutation examples
Substitution of bases
Base insertion and deletion causing frameshifts
What is the most common genetic disease and what does it do?
Sickle-cell anemia causes the haemoglobin molecules to stick together when in tissues of low oxygen concentration, which can lead to the blocking of capillaries
What type of process is meiosis?
Reduction division
In meiosis, what is the nucleus at the beginning and at the end?
Diploid nucleus (2n) --> haploid nucleus (n)
How many divisions does meiosis consist of?
What happenes to the parent cell during meiosis?
The one diploid parent cell divides into four genetically distinct haploid daughter cells
What occurs prior to meiosis?
Interphase
How much of meiotic division time is prophase one?
90%
In meiosis what happenes first during prophase one?
Chromosomes condense
Nuclear membrane breaks down
Nucleoli disappear
Spindle apparatus appears
In meiosis during prophase one, what happenes when the chromatids appear?
Homologous chromosomes come together and pair to form a BIVALENT
In meiosis during prophase one, how many chromatids does the bivalent have?
4 chromatids (2 from each chromosome)
In meiosis during late prophase one, what happenes to the bivalents
Their chromatids exchange segments in a process called crossing over
What is the place on the chromatids called where the crossing over takes place?
Chiasma
In meiosis what occurs at the very end of prophase one?
The paired chromosomes are moved by microtubules in the spindle apparatus toward the equator of the cell
In meiosis what is the first thing to happen in metaphase one?
Homologous chromosomes line up side by side on the equator
In meiosis during metaphase one, what happens after the homologous chromosomes have aligned at the equator of the cell?
Microtubules attach to the centromeres and pull them toward the poles
This is independent assortment (random orientation)
In meiosis what happens during anaphase one?
Homologous chromosomes seperate and move towards opposite poles
In meiosis what happens during telophase one?
Nuclear envelopes form and the cell starts to cleave
In meiosis what happenes at the end of the first division?
Cytokinesis
In meiosis what happens during prophase two?
Chromosomes condense
Spindle apparatus forms
Chromosomes move to the equator
In meiosis what happens during metaphase two?
Chromosomes line up at the equator and centromere divides into two
In meiosis what happens during anaphase two?
Sister chromatids are seperated and moved to opposite poles
In meiosis what happens in telophase two?
Complete haploid set of chromosomes at each pole; encapsulated in nuclear membrane
Nucleoli reform and cytokinesis occurs
What is non-disjunction?
When there is an error during meiosis, specifically at anaphase when homologous chromosomes don't seperate evenly
What is the problem caused by non-disjunction?
If a gamete is then involved in fertilisation the resultant individual has either 45 or 47 chromosomes, leading to a range of disorders
What is the cause of down syndrome?
3 chromosome 21's instead of 2
What are the effects of down syndrome?
Hearing loss
Visual disorders
mental and growth retardation
What is done to prevent down syndrome?
It is being tested for in expectant mothers
How is down syndrome tested for?
A maternal bood test records HCG (Human Chorionic Gonadotropin) and AFP (Alpha-fetoprotein) levels, chemicals released during pregnancy
A lower level of AFP and doubled level of HCG indicates a high chance of down syndrome
Further tests would then be carried out
How can chromosome abnormalities be confirmed?
Through a karyotype; an organised image of chromosomes at metaphase
Where can samples for a karyotype be taken from?
The amniotic fluid or placenta
