Chapter 2.2 Flashcards
(43 cards)
What is the synaptonemal complex?
The synaptonemal complex is a group of proteins that holds the two homologous chromosomes together in the tetrad.
What does it mean to say genes are linked?
Crossing over is a geographical phenomenon. That is to say, when crossing over occurs, a variable region of DNA at and surrounding the chiasma will cross over. This means that, the closer that genes are to one another, the better chance that they will either both be left on a chromosome or they will both cross over to the other chromosome. Either way, because of their proximity on the chromosome, they will travel together, and are therefore linked.
How does recombination unlink linked genes?
It is statistically unlikely to happen, but sometimes the region of DNA that gets swapped includes one gene but does not include another gene that is close by. The close by gene will usually be included in the cross over, but sometimes it will fall just outside of the range of crossing over. This seperates the linked genes, thereby unlinking them.
What is Mendel’s Second Law of classical genetics?
Mendel’s Second Law, the law of independent assortment, says that the inheritance of one allele of one gene has no affect on the inheritance of another allele of a different gene. For example, the second law states that, if there are two alleles for different genes, let’s say blue for eyes and blonde for hair, these two alleles will independently assort. So, if you get the allele for blue eyes, it has no affect on whether or not you get the allele for blond hair.
Is Mendel’s second law of genetics accurate?
Kind of. Unlinked genes independently assort and crossing over can even make it possible to independently assort linked genes; but the fact of the matter is that genes that are close to one another on the chromosome are more likely to be inherited together (not independent of one another like the second law claims.)
What happens in Metaphase I of Meiosis and how is it different than mitosis?
In metaphase 1, Tetrads attach to the spindle apparatus at their kinetochores and align at the center of the cell.
Key difference: In mitosis each chromosome is aligned directly over the plate with two sprindle fibers (one on each side, 2 chromatids wide on plate) whereas in meiosis homologous chromosomes are lined up with one spindle (4 chromatids wide, 2 on each side of equitorial plate, No centromeres directly over plate in meiosis)
How is the way the chromosomes are split different in Anaphase 1 of Meiosis when compared to Anaphase of Mitosis?
In Anaphase of Mitosis, the chromosomes are split according to their sister chromatids, and therefore each cell gets 2 single stranded copies of each chromosome.
In Anaphase 1 of Meiosis, the chromosomes are split according to their homologs, and therefore each cell gets 1 double stranded copy of each chromosome.
What happens in Anaphase I of Meiosis and how is it different than Anaphase of Mitosis?
In Anaphase 1 of Meiosis, the chromosomes are pulled to opposite sides of the cell, just like in Anapase of Mitosis. The only difference is that Anaphase 1 of Meiosis results in a decrease in ploidy in the daughter cell where as Anaphase of Mitosis does not.
What is disjunction?
Disjunction is the term used to refer to the separation of homologous chromosomes in Meiosis.
What is non-disjunction?
Non-disjunction is when the homologous chromosomes fail to seperate correctly. This results in inappropriate numbers of chromosomes in daughter cells.
What is Mendel’s first law of genetics?
Mendel’s first law of genetics is the law of segregation. It states that every individual organism contains two alleles for each trait, and that these alleles segregate during meiosis so that each gamete only receives one allele. The result is that, after two gametes combine, the offspring will have two alleles, one from each parent.
What stage of Meiosis is responsible for Mendel’s first law of genetics?
The disjunction of chromosomes in Anaphase 1 of Meiosis results in the separation of homologous chromosomes (upon which the two different alleles will be found) and therefore is responsible for Mendel’s first law of genetics.
What stage of Meiosis is responsible for Mendel’s second law of genetics?
For genes on the same chromosome, Crossing over in Prophase I allows genetic information to be traded between homologous chromosomes, which allows for the unlinking of linked genes and the independent assortment that Mendel’s second law of genetics describes.
For genes on different chromosomes, random alignment during metaphase results independent assortment
What is segregation in the context of a reproducing cell?
Segregation is another term that refers to the separation of homologous chromosomes.
What happens in Telophase I of Meiosis and how is it different from Telophase I of Mitosis?
Telophase I of Meiosis is basically identical to Telophase of Mitosis. The nuclear envelope reforms, the spindle retracts, etc.
What is interkinesis?
Interkinesis is a short rest period that cells can undergo after the first round of cytokinesis in Meiosis. During this period the chromosomes partially uncoil.
What is Cytokinesis?
Cytokinesis is when a microfilament ring in the center of the cell contracts to form a cleavage furrow and eventually split the cell in two.
What is a cleavage furrow?
Cleavage furrow is the name of the pinched in spot where the microfilament ring contracts in order to cause cytokinesis of the cell.
What happens in Meiosis II?
All four steps of Meiosis II are basically identical to Mitosis. In this second round of division, the sister chromatids separate, just like in Mitosis. The result is two cells with one double stranded copy of each chromosome turn in to four cells with one single stranded copy of each chromosome. I.e, 4 haploid cells.
How is biological sex determined?
Biological sex is determined by the 23rd pair of chromosomes, the sex chromosomes. If you have two X copies of a sex chromosome, you will be born a woman. If you have an X and a Y copy of a sex chromosome, you will be born a man.
How does the Y copy of the sex chromosome compare to the X copy of the sex chromosome?
Compared to the X chromosome, the Y chromosome is small and does not contain much coding information. Because of this, males rely on the X chromosome to provide most of the DNA for the non sex related information on the sex chromosomes.
What is a carrier in the context of genetics?
A carrier, in genetics, is someone who has one copy of a recessive allele, and can therefore pass a recessive phenotype to their children without having that phenotype themselves.
In a developing embryo, what can the primitive gonads eventually develop into?
The primitive gonads will develop into Testes if there is a Y chromosome or Ovaries if there are only X chromosomes.
What are the two functional components of the Testes?
- Seminiferous Tubules
- Interstitial cells (of Leydig)
