Genetics (Biology) Flashcards
Describe the chromosomal arms and regions.
There is a long arm and short arm, a centromere in the length of the chromosome and telomeres at the tips.
Define the karyotype.
The complete set of metaphasic chromosomes in a cell of a species.
Define the karyotype.
The complete set of metaphase chromosomes in a cell of a species.
How is a karyotype prepared in order to study it?
Mitosis needs to be induced in those cells. After collecting the cells, they are put in vitro in culture. Once some time has passed, this process is stopped with another type of molecule called the mitotic blocker. Consequently there are now many cells which have entered mitosis.
Then they undergo many processes and different rounds of centrifuge, before being stained to be studied under a microscope.
Describe a technique for banding a metaphase chromosome.
G banding using Giemsa dye, the number of bands are different in metaphase vs prophase, as well as specific for the species.
Although the chromosomal number is not enough as there are several different species that share the same number of chromosomes.
What is heteromorphism?
Sex chromosomes are different, they have different shapes and also contains sets of genes which are almost completely different.
What are PARs regions?
X and Y chromosomes have some regions called PARs which contain the same sets of genes.
These regions, being homologous, behave as autosomal chromosomes. For instance they can cross over during meiosis.
Describe genetic mosaicism.
If a mutation occurs after fertilisation during embryonic development, this is a postzygotic mutation. In this case
Describe genetic mosaicism.
If a mutation occurs after fertilisation during embryonic development, this is a postzygotic mutation. In this case only the cells derived from the mutated cells will have this mutation.
As a result the organism affected by this will have some parts of the body affected and others not.
What is a genotype?
A mixture of factors, a function of genes and their product and environmental influences.
What is a phenotype?
The appearance of a physical characteristic. This is not something that can necessarily be seen, but something that can be measured.
What is a character?
A characteristic that can be measured or seen which is inherited
What is a trait?
One of the variant forms of a character, e.g. while or purple flower.
What is an allele?
The genotype counterparts of a trait.
Describe the method of Mendel’s initial experiment.
He crossed the parental pea generation by removing the stamen from purple flowers and transferring sperm bearing pollen from the stamens of white flowers to the carpel of purple flowers.
After their seeds were plantes, this produced the hybrid F1 generation, which were all purple flowers.
He then crossed the F1 generation using the same method to produce the F2 generation, this results in a mix of purple and white flowers in a 3:1 ratio.
What is Mendel’s law of segregation?
The 2 members of a gene couple (2 alleles) segregate during the formation of gametes.
Describe the test-cross experiment in determining genotype.
Cross a dominant phenotype (unknow genotype) PP with a recessive phenotype pp.
If the resulting generation shows all dominant phenotypes, then the unknow genotype was PP.
If the result is half dominant and recessive phenotypes, then the unknow was Pp.
What does X-linked mutations affect?
Affects genes located on the x chromosome. The male to male transmission is possible and males are more frequently affected. Thus, males and females have different possibilities of inheriting the mutated gene.
What is autosomal dominant?
For the allele to be expressed, only one copy of the relative gene is present.
What is autosomal recessive?
Where 2 copies of the allele is needed to be affected.
Where is the SRY gene? What does it do?
The SRY gene on the Y chromosome codes for the development of testes.
The SRY gene is present on the short arm of the Y chromosome.
How does the SRY gene carry out its function?
The SRY gene encodes for protein TDF, a soluble factor which induces the formation of the medulla of the embryonic gonads to become the testis.
Describe how sex-linked genes are involved in genetic diseases in humans.
The X chromosome usually carries genes for diseases, as its larger.
A male is more likely to be affected by X-linked trait as females carry 2 X chromosomes, therefore the dominant allele is expressed.
While males only have 1 X chromosome, therefore any conditions linked to the X chromosome will be expressed.
Describe the condition hemophilia.
Hemophilia is the absence of coagulation factors, it can be either hemophilia A or B. Clotting requires a series of steps, if one is missing, blood cannot clot which is extremely dangerous.
This is an example of a X-linked condition.
Describe the condition X-linked hypophosphatemia (XLH).
X-linked dominant.
X-linked hypophosphatemia (XLH) is due to the mutation of the PHEX gene. This encodes Phosphate-regulating neutral Endopeptidase.
This mutation causes abnormalities in the joints, bones and teeth.
What happens if the X-linked allele is dominant?
A father with this condition can never transmit to a son, but can always transmit to a daughter.
What is incomplete dominance?
The phenotype of the F1 generation is between the phenotypes of the parental varieties.
What is complete dominance?
Occurs when phenotype of the heterozygote and dominant homozygote are identical.
When one allele is completely dominant over the other,
What is codominance?
2 dominant alleles that can affect the phenotype in separate distinguishable ways, they are both expressed.
What is epistasis?
One gene interferes with another gene’s expression.
