13 Meiosis & sexual life cycles

Question 1

Define heredity, variation & genetics

Answer 1

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

Question 2

What is a gene? What are the animal and plant cells that transmit them called? What are the ones that don’t called?

Answer 2

A gene is a hereditary unit, it is transmitted through gametes, as opposed to somatic cells

Question 3

Differentiate between asexual and sexual reproduction.

Answer 3

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

Question 4

What is a life cycle?

Answer 4

It is the sequence of the reproduction activity of an organism, from its conception to the production of its own offspring

Question 5

What is a karyotype? How can it be prepared?

Answer 5

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.

Question 6

What are homologuous chromosomes or homolgues?

Answer 6

Homologues are two chromosomes that have the same length, centromere position, and staining pattern, and thus carry genes that control the same inherited character

Question 7

What is an important exception to the general pattern of homologous in human somatic cells ? What do they determine?

Answer 7

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.

Question 8

What is a diploid cell? What is its number of chroms abbreviated as? What does the n represent?

Answer 8

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.

Question 9

Are gametes diploid cells? Why or why not?

Answer 9

They’re not, they’re haploid because they have a single set of chromosomes

Question 10

When does a human life cycle begin? What does it result in?

Answer 10

During the union of gametes or fertilization: when a haploid sperm fuses with the haploid egg.
This results in a fertilized egg or zygote.

Question 11

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?

Answer 11

The gametes, or the reproductive cells. They develop from specialized germ cells in the gonads (the ovaries or the testes).

Question 12

What helps gametes to remain haploid cells, and stops two gametes from forming a zygote with twice the number of chroms, or 92?

Answer 12

The process of cell division, meiosis.

Question 13

Explain three types of sexual life cycles, and note the common feature in all three.

Answer 13

• 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

Question 14

Explain the process of alternation of generation in plants and algae.

Answer 14

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.

Question 15

What is an allele?

Answer 15

Different variation of a gene

Question 16

Compare mitosis and meiosis in terms of DNA replication, number of divisions, and synapsis of chroms

Answer 16

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

Question 17

Compare mitosis and meiosis in terms of number of daughter cells, genetic composition and role in the human body

Answer 17

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

Question 18

List the three events that are unique to meiosis

Answer 18

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

Question 19

Explain independent assortment of chromosomes

Answer 19

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.

Question 20

Explain crossing over

Answer 20

Mechanism that produces recombination chroms or individual chroms that carry genes derived from both parents

Question 21

List three mechanisms that contribute to genetic vairation

Answer 21

Independent assortment
Crossing over
Random fertilization

Question 22

Explain random fertilization

Answer 22

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)

Question 23

What is a gamete?

What are somatic cells? What is a locus (pl. loci)?

Answer 23

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.

Question 24

What are autosomes?

Answer 24

They are any other chromsomes in the cell beside the sex chroms.

Question 25

Differentiate between sister chromatids and nonsister chromatids in terms of production and roles

Answer 25

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

Question 26

What takes place before prophase I to the chromosomes?

Answer 26

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

Question 27

What is a chiasmata?

Answer 27

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

Question 28

What happens during prophase I to chromosomes, the microtubules, and nucleur envelope

Answer 28

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

Question 29

What happens during prophase II?

Answer 29

A spindle apparatus forms and chroms move toward metaphase plate

Question 30

What happeins during metaphase I to kinetochores and microtubules?

Answer 30

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

Question 31

What happens during anaphase I to homologues and cohesive proteins?

Answer 31

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

Question 32

What happens during telophase I and cytokenesis?

Answer 32

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

Question 33

Describe the purpose of meiosis II.

Answer 33

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

Question 34

What happens during metaphase II to the kinetochores and chroms.

Answer 34

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

Question 35

What happens during anaphase II to centromeres and chromatids

Answer 35

Proteins holding chromatids together at centromere breakdown. the chromatids move toward opposite poles as indivdual chromosomes

Question 36

What happens during telophase II and cytokenesis?

Answer 36

Nuclei form, chroms begin decondensing and cytokenesis occurs. The four resulting cells are each genetically distinct from one another

Question 37

Is XY sex chrom male or female? What about XX?

Answer 37

Females have a homologuous pair of X chroms (XX) while males have 1 X and 1 Y that are only partly homologous

Question 38

Explain the variety of life cycle in animals. Discuss the production of gametes and when mitosis occurs

Answer 38

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

Question 39

Explain the type of life cycle most fungi and protists have. Start from the gamete fusion.

Answer 39

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

Question 40

What are recombinant chromosomes?

Answer 40

They are indivdual chromsomes that carry genes from both parents

Question 41

What is the original source of genetic variation?

Answer 41

A mutation

Question 42

How is meiosis II similiar to mitosis?

Answer 42

Sister chromatids seperate during anaphase