Campbell and Reece 8th edition Cell Biology

[Stephen1993]

hello again

this is about mitosis and meiosis
what does "synapsis of homologous chromosomes" mean?
does not occur in mitosis and
occurs during prophase I along with crossing over between non-sister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion for meiosis

thank you

 

[bobze]

hello again

this is about mitosis and meiosis
what does "synapsis of homologous chromosomes" mean?
does not occur in mitosis and
occurs during prophase I along with crossing over between non-sister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion for meiosis

thank you

http://lmgtfy.com/?q=synapsis+of+homologous+chromosomes"

 

[Stephen1993]

thank you for that

Pg 297)
“As a consequence of the independent assortment of chromosomes during meiosis, each of us produces a collection of gametes differing greatly in their combinations of the chromosomes we inherited from our two parents. Figure 13.11 suggests that each individual chromosome in a gamete is exclusively maternal or paternal in origin. In fact, this is not the case, because crossing over produces recombinant chromosomes, individual chromosomes that carry genes (DNA) derived from two different parents (Figure 13.12).”
What does “Figure 13.11 suggests that each individual chromosome in a gamete is exclusively maternal or paternal in origin.” mean?

thank you

 

[atyy]

thank you for that

Pg 297)
“As a consequence of the independent assortment of chromosomes during meiosis, each of us produces a collection of gametes differing greatly in their combinations of the chromosomes we inherited from our two parents. Figure 13.11 suggests that each individual chromosome in a gamete is exclusively maternal or paternal in origin. In fact, this is not the case, because crossing over produces recombinant chromosomes, individual chromosomes that carry genes (DNA) derived from two different parents (Figure 13.12).”
What does “Figure 13.11 suggests that each individual chromosome in a gamete is exclusively maternal or paternal in origin.” mean?

thank you

A typical man's skin cells ,kidney cells, etc. have n pairs of chromosomes. In each pair of chromosomes, one is entirely from his mother, and one is entirely from his father.

When he makes sperm, each sperm contains n chromosomes. However, each of the n chromosomes in the sperm are not simply one of each of the n pairs, ie. each chromosome is not entirely from the man's father or entirely from his mother. This is because of homologous recombination during meiosis, in which homologous chromosomes pair up and exchange material, so that the resulting chromosomes each contain a mix of material from the man's father and mother. (Actually it's more complicated than this, during homologous recombination, "crossing over" happens with only one chromatid of each chromosome during meiosis.)

In http://highered.mcgraw-hill.com/olc.../120074/bio16.swf::Unique Features of Meiosis , we start off with two pairs of chromosomes (one long pair, and one short pair). In each pair, one chromosome is purple and one is blue, indicating that the chromosome is entirely from one of the man's parents. During homologous recombination, one chromatid in each pair becomes a mix of blue and purple, indicating that it is now a mix of genetic material from the man's father and mother.

 

[Stephen1993]

thank you for that

“Errors in meiosis or damaging agents such as radiation can cause breakage ofa chromosome, which can lead to four types of changes in chromosome structure (Figure 15.15). A deletion occurs when a chromosomal fragment is lost. The affected chromosome is then missing certain genes. (If the centromere is deleted, the entire chromosome will be lost.)”
what does the last sentence in the brackets mean?

thank you

 

[atyy]

thank you for that

“Errors in meiosis or damaging agents such as radiation can cause breakage ofa chromosome, which can lead to four types of changes in chromosome structure (Figure 15.15). A deletion occurs when a chromosomal fragment is lost. The affected chromosome is then missing certain genes. (If the centromere is deleted, the entire chromosome will be lost.)”
what does the last sentence in the brackets mean?

thank you

The centromere is what attaches the chromosome to the spindle. The spindle pulls the chromosome to the poles. If the centromere is deleted, the chromosome cannot attach to the spindle, and will not be pulled towards the pole. One of the 4 daughter cells will have one chromosome too few, and another will have one chromosome too many.

http://highered.mcgraw-hill.com/olc...072437316/120074/bio19.swf::Stages of Meiosis

 

[Stephen1993]

thank you for that

because the centromere attaches the chromatids together then if the centromere is deleted then the spindle cord/fibre can't pull the whole replicated chromosome but only pulls one of the chromatids?
or is the spindle fibre attach to the centromere which means that if the centromere is deleted then the whole replicated chromosome cannot be pulled?

thank you

 

[mishrashubham]

thank you for that

because the centromere attaches the chromatids together then if the centromere is deleted then the spindle cord/fibre can't pull the whole replicated chromosome but only pulls one of the chromatids?
or is the spindle fibre attach to the centromere which means that if the centromere is deleted then the whole replicated chromosome cannot be pulled?

thank you

Read what he wrote carefully again.

The centromere is what attaches the chromosome to the spindle. The spindle pulls the chromosome to the poles. If the centromere is deleted, the chromosome cannot attach to the spindle, and will not be pulled towards the pole. One of the 4 daughter cells will have one chromosome too few, and another will have one chromosome too many.

http://highered.mcgraw-hill.com/olc...072437316/120074/bio19.swf::Stages of Meiosis

 

[atyy]

Actually, I never studied this part very properly, so I'm not sure how many shades of centromere deletion can occur, or what other subtleties there may be.

 

[Stephen1993]

sorry about then

“A diploid embryo that is homozygous for a large deletion (or has a single Xchromosome with a large deletion, in a male) is usually missing a number ofessential genes, a condition that is ordinarily lethal.”
What does “A diploid embryo that is homozygous for a large deletion” mean?

thank you

 

[mishrashubham]

sorry about then

“A diploid embryo that is homozygous for a large deletion (or has a single Xchromosome with a large deletion, in a male) is usually missing a number ofessential genes, a condition that is ordinarily lethal.”
What does “A diploid embryo that is homozygous for a large deletion” mean?

thank you

These are pretty basic terms. You should try to look them up yourself on the internet first. BTW you should be well aware of these terms if you are studying university level biology.


Anyways; what the text is trying to say is that if a diploid embryo i.e. having a pair of each chromosome, is homozygous for a large deletion i.e. the deletion of a specific portion exists in both of the chromosomes of a homologous pair, it would not possesses any of the genes which were deleted and hence would face the consequences if they turn out to be essential. In case of males, they cannot rely on the other X chromosome if one suffers a deletion since they have only one X chromosomes.