Chapter 9 Flashcards
What do the offspring of asexual reproduction receive?
All offspring inherit the same number and kinds of genes of its parents.
What are Genes?
Sequences of DNA that encode heritable information about traits.
What is a Clone?
A genetically identical copy of the parent, barring mutations all offspring of asexual reproduction are clones.
What is an Allele?
Each unique molecular form of the same gene.
What are Gametes?
The mature reproductive cells formed by the meiosis of germ cells.
What is a Zygote?
The first cell of a new individual.
What does it mean if a cell has a diploid number?
It means that it has a pair of each type of chromosome.
What are Homologous Chromosomes?
A pair of chromosomes that have the same length, shape, and assortment of genes. They appear zipped together during meiosis.
True or False: In Meiosis, the cells go through two cell cycles.
True, though it only goes through interphase.
What happens in Prophase 1?
Chromosomes were duplicated earlier, in interphase. Now they start to condense. Each pairs with its homologue and swapssegments with it. New microtubules are forming a bipolar spindle. One of the two centrosomes moves to the opposite side of the nuclear envelope, which begins to break up.
What happens in Metaphase 1?
Prior to metaphase I, one set of microtubules had tethered one chromosome of each type to one spindle pole and another set tethered its homologue to the other spindle pole. A tug-of war between the two sets has now aligned the chromosomes midway between the two spindle poles.
What happens in Anaphase 1?
One of each duplicated chromosome, maternal or paternal, moves to a spindle pole; its homologue moves to the opposite pole. Motor proteins that interact with microtubules bring about the movement.
What happens in Telophase 1?
One of each type of chromosome has arrived at a spindle pole. In most species, the cytoplasm divides at this time. All of the chromosomes are still duplicated.
What happens in Prophase 2?
In each cell, one of two centrioles moves to the opposite side of the cell, and a new bipolar spindle forms. Some spindle microtubules harness one chromatid of each chromosome to a spindle pole; other microtubules harness its sister chromatid to the other pole.
What happens in Metaphase 2?
By now, microtubules from both spindle poles have finished a tug-of-war. They have aligned all of the still-duplicated chromosomes midwaybetween the poles.
What happens in Anaphase 2?
The sister chromatids of each chromosome move apart and are now individual, unduplicated chromosomes. Microtubules pull them toward opposite spindle poles as other microtubules push the poles apart. A parcel of one of each type of chromosome will end up near each pole.
What happens in Telophase 2?
A new nuclear envelope encloses each parcel of chromosomes, so there are now four nuclei. The cytoplasm divides. Each of the daughter cells now has a haploid number (n) of unduplicated chromosomes.
What does ‘Crossing Over’ mean?
A process by which a chromosome and its homologous partner exchange corresponding segments.
True or False: Crossing over between a pair of homologous chromosomesputs novel combinations of alleles in both, which results innovel variations in forms of traits among offspring.
True. Gene swapping would be pointless if each type of gene never varied.
How many possibilities of combinations are there between human sperm and eggs for maternal and paternal chromosomes?
8,388,608 (2^23) combinations.
What is a Sporophyte?
A diploid multicelled body found in most plant life cycles. Spores form in part of it.
What is Gametophyte?
A multicelled haploid body inside which one or more gametes form.
True or False: In animals, haploid germ cells give rise to gametes.
False, in animals diploid cells give rise to gametes.
What is Fertilization (in relation to sexual reproduction)?
The fusion of the haploid nuclei of two gametes.
Why does meiosis precede fertilization?
Because if it did not then the chromosome number would double every generation, which would change the individual’s hereditary information.
Sexual or Asexual Reproduction: Meiosis, gamete formation, and fertilization.
Sexual reproduction.
Why do meiosis and fertilization shuffle parental alleles?
So offspring inherit new combinations of alleles.
Does meiosis half the parental chromosome number?
Yes, then the fusion of two gamete nuclei during fertilization restore the parental chromosome number in the zygote.
What three events give rise to novel combinations of alleles?
- Crossing over to prophase 12. The random alignment of maternal and paternal chromosomes at metaphase 13. The chance meeting of gametes at fertilization
