Reproduction and cell division Flashcards
What is the locus of a gene?
The specific location of a gene on a chromosome
What is gene linkage?
The phenomenon seen where genes with similar loci are typically inherited together, since they’re unlikely to be separated during meiosis
What are two types of genetic linkage?
Autosomal linkage and sex linkage
What is autosomal linkage?
The inheritance of genes with similar loci on non-sex chromosomes together
What is sex linkage?
The inheritance of nearby genes together on the same sex chromosome. Expression of these genes is sex dependent
What is meiosis?
The process involved in the production of gametes which produces 4 genetically different haploid daughter cells
Name the stages in meiosis
Prohpase, metaphase, anaphase and telophase (there’s 2 of each)
What does the term haploid mean?
A cell which only has one set of unpaired chromosomes. This term is usually used to describe germ cells.
What does the term diploid mean?
A cell which only has a set of paired chromosomes. The term is usually used to describe somatic cells.
Describe prophase 1
The chromosomes condense, the nuclear envelope breaks down, the centrioles move to the poles of the cell and homologous pairs of chromosomes cross over
What are chiasmata?
The points where homologous chromosomes cross over in meiosis
Describe metaphase 1
The crossed over chromosomes align in the centre of the cell (at the metaphase plate)
Describe anaphase 1
The chromosomes are pulled apart by the spindle fibers
Describe telophase 1
The spindle fibers break down and nuclear envelopes begin to form around the separated sets of chromosomes
Describe prophase 2
The nuclear envelope breaks down, the chromosomes condense, the centrosomes move to opposite poles of the cell and the spindle fibers begin to form
Describe metaphase 2
The chromosomes align in the centre of the cell on the metaphase plate
Describe anaphase 2
The two sister chromatids making up each chromosome are pulled apart by the microtubules
Describe telophase 2
The nuclear envelope beings to reform, the chromosomes condense and the spindle fibers break down
How many daughter cells are formed in meiosis?
4
Which type of cell division produces diploid cells?
Mitosis
Which type of cell division produces haploid cells?
Meiosis
Describe 3 points in the process of meiosis where variation is produced
Prophase 1: chromosomes can cross over at different points.
Metaphase 1 and 2: chromosomes can line up either way around
What is the purpose of meiosis?
To produce gametes (sex cells)
Describe the structure of a mature sperm cell
Acrosome contains digestive enzymes which break down the zona pellucida of the egg. Flagellum for propulsion, many mitochondria for energy.
Describe how egg cells are adapted to their function
Haploid nucleus contains genetic material. Mitochondria produce energy for the developing embryo. Cytoplasm contains nutrients for the developing embryo. Cell membrane hardens after fertilization, preventing entry of other sperm ensuring the zygote is diploid.
Describe how sperm cells are adapted to their function
Haploid nucleus contains genetic information. Tail enables movement. Mitochondria provides energy for tail movement. Acrosome contains enzymes that digest the egg cell membrane
Describe the structure of egg cells
They have a haploid nucleus, the zone pellucida which surrounds the egg and initiates the acrosome reaction. The cytoplasm has cortical granules which prevent polyspermy and the follicle cells are involved in hormone production
Describe how egg cells are adapted to their function
They are large and contain lots of cytoplasm to support many cell divisions. They contain many nutrients to support cell division and growth. Zona pellucida to prevent polyspermy and they have a haploid nucleus which create s diploid zygote once fertilized by a sperm cell.
What is the acrosome reaction?
As a sperm cell approaches an oocyte, the acrosome
membrane fuses with the outer membrane of the sperm cell. This allows the contents of the acrosome to exit the sperm cell. The contents from the acrosome include digestive enzymes which are then able to break down the zona pellucida to allow for fertilisation
What is the cortical reaction?
The exocytosis of the contents of cortical vesicles which causes the hardening of the zona pellucida. This prevents multiple fertilization events.
Define pollination
The deposition of pollen onto a stigma from an anther
Name two types of pollination
Cross-pollination and self-pollination
What is cross-pollination?
A type of pollination in which pollen is transferred from an anther of one plant to a stigma of a different plant
What is self-pollination?
When pollen is transferred from an anther of a plant to a stigma of the same plant.
Where does double fertilization occur?
Embryo sac of ovule
How do the male nuclei reach the embryo sac?
-Pollen grain from one plant lands on the stigma of another
-mitosis of pollen grain to form a pollen tube nucleus and two male gametes
-pollen tube grows from the grain down to the ovule via the digestion of the style
-pollen tube delivers two male gametes
How does the pollen tube enter into the embryo sac?
Via the micropyle
Define micropyle
Pore in the integument of an ovule through which the pollen tube enters the embryo sac. It remains as a pore in the testa (seed coat)
What happens during double fertilization?
In the embryo sac of ovule:
-one sperm cell fertilizes an ovum to form a diploid zygote
-one sperm cell fuses with two polar nuclei to form a triploid primary endosperm
What happens to the ovule following double fertilization?
It develops into the seed
How is the diploid embryo formed after double fertilization?
Diploid zygote undergoes mitosis to form diploid embryo.
What is mitosis?
A type of cell division that produces two genetically identical daughter cells
What is the cell cycle?
A series of processes that a cell goes through to prepare it for division.
What are the two main sections of the cell cycle?
Interphase and mitosis
Name the 3 stages of interphase
Gap 1 (G1), Synthesis (S), Gap 2 (G2)
Describe the G1 phase of interphase
The first phase of interphase and it involves the growth of the cell and synthesis of molecules like proteins and DNA. The cell also duplicates its organelles in preparation for mitosis.
Describe the S phase of interphase
The second phase of the interphase, where the DNA in the cell is replicated
Describe the G2 phase of interphase
The third phase of interphase and a second growth phase where the cell continues to grow, produces more proteins and organelles and prepares for division
Name the 4 phases of mitosis
Prohpase, Metaphase, Anaphase, Telophase
Describe metaphase
The chromosomes align on the metaphase plate at their centromeres
Describe anaphase
The sister chromatids are pulled to the opposite ends (poles) of the cell by the spindle fibres
Describe telophase
The spindle fibers disassemble, the nucleus and nucleolus begin to reform and the chromosomes begin to decondense
Describe prophase
The chromosomes in the nucleus condense, the nucleolus disappears and the nuclear membrane begins to break down. Spindle fibers also begin to grow from the centrioles.
Give 3 beneficial uses of mitosis
Repair, growth, asexual reproduction
What is cytokinesis
The stage at the end of mitosis where the cytoplasm is divided in two
Describe cytokinesis in animal cells
A contractile ring is formed around the centre of the cell which tightens and pinches the two cells in the middle. This eventually pinches off to create two new cells
Describe cytokinesis in plant cells
Vesicles are released from the ER and accumulate in the middle. The vesicles fuse together to form a cell plate which is then used to form new cell walls for each new cell.
How are mitotic indices calculated?
By dividing the number of cells currently undergoing mitosis by the total number of cells.
