Biology AQA A level - Meiosis | Quizlet

what is a haploid cell?

A cell with half the number of centromeres as a diploid cell.

What is a diploid cell?

Cell with two sets of chromosomes, one from each parent. (2n)

what are gametes?

sex cells (sperm and egg)

How many division are involved in meiosis?

2, named meiosis II and meiosis I

describe the process of prophase I.

DNA condenses and becomes visible.

Each chromosome contains two sister chromatids.

Homologous chromosomes are arranged next to each other.

Crossing over of non sister chromatids occurs at a 'Chiasma'

Spindle forms and nuclear envelope breaks.

define bivalent.

a pair of homologous chromosomes

what happens in metaphase I?

bivalents line up along the equator of the spindle

Describe Anaphase I.

homologous chromosomes are separated to opposite ends of the spindle by microtubules.

Centromeres are not split

What occurs during Telophase I

Spindle fibres being to break down.

chromosomes arrive at opposite poles.

Nuclear envelopes form around the two groups of chromosomes and nucleoli reform.

some plant cells go straight to meiosis II without telophase I.

Describe cytokinesis in plant cells.

vesicles from the Golgi apparatus gather along the equator of the spindle. The vesicles merge to form new cell surface membrane and secrete a layer of calcium pectate which become the middle lamella. Cellulose is layered on the middle lamella to form the primary and secondary walls of the cell.

Is there a second interphase between meiosis I and meiosis II?

No, hence DNA is not replicated.

What is special about prophase II?

The new spindle forms at a right angle to the previous one.

What is special about anaphase II?

chromatids are pulled apart, hence, 'single armed chromosomes'. As there is still the same number of centromeres, the cells are diploid.

What is the process of 'crossing over' and how does this increase genetic diversity?

process by which non-sister chromatids exchange alleles.

-during meiosis one, non sister chromatids are in close proximity and can 'cross over'.

-This crossing point is called a chiasmata.

- Stress is placed on the DNA and a section of chromatid from one chromosome may break and re-join with the chromatid from the other chromosome.

-This swapping of alleles is significant as it can result in a new combination of alleles on the two chromosomes. (usually more than one chiasmata and more likely to form away from the centromere.)

Describe independent assortment

homologous chromosomes line up randomly on the equator of the cell. Chromosomes can line up on the left or right side randomly, leading to different alleles which contributes to genetic variation.

what is a zygote?

fertilized egg cell

What is the formula for the number of different chromosome combinations in two gametes from meiosis?

2^n where n is the number of homologous chromosome pairs.

when fertilisation occurs what is the number of combinations of chromosomes in zygotes?

(2^n)^2