13 Meiosis & sexual life cycles Flashcards
Define heredity, variation & genetics
Heredity is the transmission of genetic information from one generation to the next
Variation is the difference in genetic info from one gen to the next
Genetics is study of heredity and hereditary variation
What is a gene? What are the animal and plant cells that transmit them called? What are the ones that don’t called?
A gene is a hereditary unit, it is transmitted through gametes, as opposed to somatic cells
Differentiate between asexual and sexual reproduction.
Asexual reproduction brings about offspring that are exact genetic copies of their parents, or a clone. It only needs one parent who passes all of its genes without any gamete fusion.
Sexual requires two parents who, through gamete fusion, produce an offspring with a unique genetic combination inherited from both, giving rise to genetic variation
What is a life cycle?
It is the sequence of the reproduction activity of an organism, from its conception to the production of its own offspring
What is a karyotype? How can it be prepared?
A karyotype is a display of chromosomes in pairs starting from the longest.
It is prepared by isolating somatic cells, stimulated to undergo mitosis, and grown in culture for a few days. They are arrested at metaphase, in their most highly condensed form, are stained and a photo is captured. The computer then arranges them into pairs.
What are homologuous chromosomes or homolgues?
Homologues are two chromosomes that have the same length, centromere position, and staining pattern, and thus carry genes that control the same inherited character
What is an important exception to the general pattern of homologous in human somatic cells ? What do they determine?
The sex chroms. In humans, females have a homologous pair of X chroms while males have 1 X and 1 Y with only small parts of each that are homologous.
They determine an organism’s sex.
What is a diploid cell? What is its number of chroms abbreviated as? What does the n represent?
A cell that has two chrom sets, one maternal and one paternal. Its diploid number of chromosomes is abbreviated as 2n where n represents the number of chroms in a single set.
Are gametes diploid cells? Why or why not?
They’re not, they’re haploid because they have a single set of chromosomes
When does a human life cycle begin? What does it result in?
During the union of gametes or fertilization: when a haploid sperm fuses with the haploid egg.
This results in a fertilized egg or zygote.
What are the only cells in the human body that are not produced through mitosis of the zygote? How then are they produced? What is the purpose of this?
The gametes, or the reproductive cells. They develop from specialized germ cells in the gonads (the ovaries or the testes).
What helps gametes to remain haploid cells, and stops two gametes from forming a zygote with twice the number of chroms, or 92?
The process of cell division, meiosis.
Explain three types of sexual life cycles, and note the common feature in all three.
- Animals: gametes are the only haploid cells and are unicellular
- plants and some algae: alternation of generations
- Most fungi and protists: meiosis produces haploid cells that then divide through mitosis
Explain the process of alternation of generation in plants and algae.
Life cycle of plants and some algae; both diploid and haploid stages are multicellular. The multicellular diploid stage is called sporophyte. It undergoes meiosis and produces a spore, which in turn divides mitotically. This produces a gametophyte, the multicellular haploid stage.
The cells of this gametophyte give rise to haploid gametes, which fuse to result in a diploid zygote.
To sum it up, the sporophyte generation produces a gametophyte, and the gametophyte generation produces the next sporophyte.
What is an allele?
Different variation of a gene
Compare mitosis and meiosis in terms of DNA replication, number of divisions, and synapsis of chroms
DNA replication occurs in interphase (S) before mitosis begins; occurs in interphase before meiosis I begins
Number of divisions: only one in mitosis with PMAT phases; two in meiosis each with their won PMAT phases
Synapsis of chroms: does not occur in mitosis; occurs during prophase I as crossing over takes place
Compare mitosis and meiosis in terms of number of daughter cells, genetic composition and role in the human body
Number of daughter cells: two diploid cells that are genetically identical to parent cell in mitosis; four haploid cells each with own unique genetic composition in meiosis
Role: Mitosis’ role is growth, repair and development; while meiosis’ role is producing gametes and introducing genetic variability
List the three events that are unique to meiosis
Synapsis and crossing over; homologuous pairs at the metaphase plate compared to the individual chroms in mitosis; duplicated chrmosomes remain attached whereas in mitosis sister chromatids seperate
Explain independent assortment of chromosomes
the first meiotic division results in in each homologue pair sorting its maternal & paternal homolgues independently of each other because they are positioned independently of other pairs during metaphse. The number of possible combinations of chroms in the resulting gametes is 2 to the power of n.
Explain crossing over
Mechanism that produces recombination chroms or individual chroms that carry genes derived from both parents
List three mechanisms that contribute to genetic vairation
Independent assortment
Crossing over
Random fertilization
Explain random fertilization
The fusion of a female gamete and a male gamete will produce a zygote with any of the 2 to the 26 diploid combinatios (2^23 * 2^23)
What is a gamete?
What are somatic cells? What is a locus (pl. loci)?
A gamete is a reproductive cell that transmit genes from one generation to the next. Somatic cells are any cells besides gametes that have 46 chroms or 2n. A locus is a specific location on a gene.
What are autosomes?
They are any other chromsomes in the cell beside the sex chroms.
Differentiate between sister chromatids and nonsister chromatids in terms of production and roles
Sister chromatids are two copies of the same chromatid having the same gene/alleles. They are produced during S phase of interphase and are used in cell division for things like devleopment, growth
Nonsister chromatid pair carry one strand from the mother and one from the father carry genes controlling the same character. They are produced during metaphase of meisois and are used for reproduction o
What takes place before prophase I to the chromosomes?
Chomosmes condense, Homologues pair loosely so that they are aligned gene by gene. Paired homologues connect again by protein called the synaptonemal complex, they are now in synapsis.
Corssing over takes place beginning from the formation of the synaptonemal complex and is completed while they are in synapsis
What is a chiasmata?
Site of crossing over. It is an X-shaped region in each homologous pair in which they remain in contact at the point where the crossover has occured. This happens due to the cohesion of the two original sister chromatids that still holds them together
What happens during prophase I to chromosomes, the microtubules, and nucleur envelope
Prophase I: synapsis ends, chromsomes in each pair move apart slightly but have chiasmatas now. Centrosome movement, spindle formation, and nuclear envelope breakdown take place. Microtuubles from each pole attach to kinetochores and homolgoues move toward metaphase plate
What happens during prophase II?
A spindle apparatus forms and chroms move toward metaphase plate
What happeins during metaphase I to kinetochores and microtubules?
Pairs of homologues are now arranged at the metaphase plate. Both chromatids of each homologue is attached to kinetochore microtubule from one pole and those from the other homologue are attached to opposite pole
What happens during anaphase I to homologues and cohesive proteins?
Proteins that cause sister chromatid cohesion breakdown along the arms only. Homologues seperate and move toward opposite poles as a chromatid unit guided by the spindle apparatus. Cohesion presists along centromere
What happens during telophase I and cytokenesis?
At this point, each half of the cell has a complete haploid set. Each chromosome is made of two sister chroamtids and one or both chromatids contain a region of nonsister chromatid DNA. A cleavage furrow/cell plate forms
Describe the purpose of meiosis II.
It is another round of cell division in each of the two haploid cells formed through meiosis I where sister chromatids finally separate. The result is four haploid daughter cells containing unduplicated chromsomes
What happens during metaphase II to the kinetochores and chroms.
Chroms are now along metaphase plate but the two sister chromaitds are not identical. The kinetochores from each sister chromatid is attached to microtubule extending to pole
What happens during anaphase II to centromeres and chromatids
Proteins holding chromatids together at centromere breakdown. the chromatids move toward opposite poles as indivdual chromosomes
What happens during telophase II and cytokenesis?
Nuclei form, chroms begin decondensing and cytokenesis occurs. The four resulting cells are each genetically distinct from one another
Is XY sex chrom male or female? What about XX?
Females have a homologuous pair of X chroms (XX) while males have 1 X and 1 Y that are only partly homologous
Explain the variety of life cycle in animals. Discuss the production of gametes and when mitosis occurs
In animals, gametes are the only haploid cells. Germ cells undergo meiosis as they turn to gametes, and remain unicellular. After fertilization takes place and a zygote forms, mitosis takes place to produce a diploid organism
Explain the type of life cycle most fungi and protists have. Start from the gamete fusion.
In these organisms, after two gametes form a diploid zygote, meiosis takes place. However, it gives rise to haploid cells that then divide to produce unicellular or multicellular adults. Therefore, the only diploid stage in this type of life cycle is the unicellular zygote
What are recombinant chromosomes?
They are indivdual chromsomes that carry genes from both parents
What is the original source of genetic variation?
A mutation
How is meiosis II similiar to mitosis?
Sister chromatids seperate during anaphase
