Reproduction & Development Flashcards
What is crossing over?
Crossing over is when non-sister chromatids exchange alleles (different versions of genes).
During meiosis 1, homologous pairs line up, leading to them becoming tangled, creating tension on the DNA molecules which causes the chromatid to break and rejoin on the other chromosome.
What is independent assortment?
Independent assortment leads to the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase.
What happens during Prophase I?
DNA condenses and becomes visible as chromosomes. DNA replication has already occurred, so each chromosome consists of two sister chromatids joined together by a centromere. The chromosomes are arranged side by side in homologous pairs.
A pair of homologous chromosomes is called a bivalent.
What occurs during crossing over in Prophase I?
As the homologous chromosomes are very close together, the crossing over of non-sister chromatids may occur. The point at which the crossing over occurs is called the chiasma (chiasmata; plural).
What structural changes occur in Prophase I?
Centrioles migrate to opposite poles, and the spindle is formed. The nuclear envelope breaks down, and the nucleolus disintegrates.
What happens during Metaphase I?
The bivalents line up along the equator of the spindle, with the spindle fibres attached to the centromeres.
What occurs during Anaphase I?
The homologous pairs of chromosomes are separated as microtubules pull whole chromosomes to opposite ends of the spindle. The centromeres do not divide.
What happens during Telophase I?
The chromosomes arrive at opposite poles. Spindle fibres start to break down. Nuclear envelopes form around the two groups of chromosomes, and nucleoli reform. Some plant cells go straight into meiosis II without reformation of the nucleus in telophase I.
What is Cytokinesis?
This is when the division of the cytoplasm occurs. Cell organelles also get distributed between the two developing cells. The end product of cytokinesis in meiosis is two haploid cells.
What is the second division of meiosis called?
Meiosis II
Is there an interphase between meiosis I and meiosis II?
No, there is no interphase between meiosis I and meiosis II, so the DNA is not replicated.
How does meiosis II compare to mitosis?
The second division of meiosis is almost identical to the stages of mitosis.
What happens during Prophase II?
The nuclear envelope breaks down and chromosomes condense. A spindle forms at a right angle to the old one.
What occurs during Metaphase II?
Chromosomes line up in a single file along the equator of the spindle.
What happens during Anaphase II?
Centromeres divide and individual chromatids are pulled to opposite poles, creating four groups of chromosomes that have half the number of chromosomes compared to the original parent cell.
What occurs during Telophase II?
Nuclear membranes form around each group of chromosomes.
What is the final step of meiosis II?
Cytokinesis occurs, where the cytoplasm divides as new cell surface membranes are formed, creating four haploid cells.
What is the chromosome count in the resulting cells after meiosis II?
The cells contain the same number of centromeres as they did at the start of meiosis I but now only have half the number of chromosomes.
What are the main components of the reproductive system?
The reproductive system consists of the ovaries, fallopian tubes, uterus, vagina, external genitalia, and breasts.
What is the function of the vagina?
The vagina extends from the cervix to the external genitalia and aids conception by receiving the penis and semen during sexual intercourse.
What is the structure of the vagina?
The vagina is made up of smooth muscle and a mucosal inner lining.
What is the primary function of the uterus?
The uterus is responsible for the growth of an implanted fetus.
What are the three layers of the uterus?
The three layers of the uterus are the perimetrium, myometrium, and endometrium.
What is the perimetrium?
The perimetrium lines alongside the peritoneum.