Genetics Flashcards
Explain the process of Down syndrome.
There are three sets of chromosomes of type 21, instead of two. This means a total of 47 chromosomes are present instead of the normal 46. The non disjunction may have happened during the formation of eggs or sperms. Down syndrome risk increases with age.
Explain how amniocentesis works.
Amniotic fluid is collected from the amniotic sac around the fetus. A sample of this is taken. This is done by a hypodermic needle inserted through the abdomen wall and uterus wall. Amniotic fluid is drawn out into a syringe. It contains fetal cells.
Explain how chorionic villus sampling works.
Cells are removed from the fetal tissues in the placenta called chorionic villus. A hypodermic needle is inserted through the abdomen wall and uterus wall and is used to obtain fetal cells.
What is karyotping
In both amniocentesis and chorionic villus sampling, the fetal cells are then incubated by chemicals to stimulate mitosis. Another chemical then stops the mitosis at metaphase, because this is when the chromosomes are the most visible. A fluid is used to burst the cell and the chromosomes spread out. The burst cells are examined under the microscope. A photograph is taken of the chromosomes. They are then cut out and arranged into pairs based on structure and size. This is karyotping.
Define genotype.
It is the alleles possessed by a gene.
Define phenotype.
The characteristics of an organism.
Define locus.
The particular position on a homologous chromosome of the gene.
Define homozygous.
Having two identical alleles of a gene.
Homozygote: all gametes have the same allele.
Define heterozygous.
Having two different alleles of a gene
Half of the gametes of a heterozygote have one of the alleles and the other half has the other allele.
Define co dominant allele.
An allele that has the same effect on the phenotype in a heterozygous individual as in a homozygous individual.
Define recessive allele.
An allele that has an effect only on the phenotype of homozygous individuals. In heterozygous, this allele is hidden by the dominant allele.
What is a carrier?
A carrier is an individual Who has a recessive allele which causes a genetic disease for an individual who is homozygous for this allele.
What is test crossing?
In a test cross, an individual that might be heterozygous is crossed with an individual that is homozygous recessive.
What are codons ant alleles?
Alleles that both affect the phenotype when present In a heterozygote.
What is non disjunction?
When the chromosomes fail to separate properly during a Anaphase 1 or anaphase 2.. Which leads to the production of gametes with too many or too few chromosomes. Ones with too few die. But ones with many survive. If the one with too many is fertilized, then the zygote has three chromosomes of one type instead of two.
