Genetic diversity as a result of meiosis

What is meiosis and what does it produce

A type of cell division that produces daughter cells with:

-half the number of chromosomes as the parent cell

-different combinations of alleles from each daughter cell and the parent cell

What are the starting and ending chromosome states in meiosis?

Meiosis starts with diploid cell and ends with haploid cells.

Why is meiosis important?

It produces haploid gametes for sexual reproduction and creates genetic variation, which increases diversity allowing natural selection.

What is a centromere?

The part of a chromosome where two chromatids are held together in which in the becomes sister chromatids, found at the centre of the chromosome

What are homologous chromosomes?

Pairs of chromosomes, one from each parent, that contain the same genes and are of the same size.

What is the difference between chromatids and sister chromatids

A chromatid is one of two identical strands of a chromosome and sister chromatids are formed when a chromatid is replicated

What does the acronym IPMATPMAT stand for in meiosis?

Interphase, Prophase I, Metaphase I, Anaphase I, Telophase I, Cytokinesis, Prophase II, Metaphase II, Anaphase II, Telophase II, Cytokinesis.

What happens during interphase?

DNA is replicated, resulting in chromosomes that contain two chromatids so has become a sister chromatid

What occurs during Prophase I of meiosis?

Chromosomes condense, homologous chromosomes pair up, and spindle fibres start forming.

What happens during Metaphase I?

Homologous chromosomes line up along the equator of the cell and attach to spindle fibers by their centromeres.

What happens during Anaphase I?

Homologous chromosome pairs are separated and pulled to opposite poles of the cell.

What occurs during Telophase I and cytokinesis?

Chromosomes reach opposite poles, the cell pinches in the middle, and the cytoplasm divides to form two cells.

What occurs during Prophase II?

There are now two daughter cells

The chromosomes condense and centrioles migrate to opposite poles of the cell where each centriole starts forming spindle fibres

What happens during Metaphase II?

The chromosomes line up at the equator of the cell

Each chromosome attaches to the spindle by their centromere

What happens during Anaphase II

At the centromeres the chromosomes divide and separate each pair of chromatids

What happens during Telophase II and Cytokinesis?

The chromatids reach the opposite poles of the cell and the cell pinches in the middle

The cytoplasm divides (cytokinesis) and 4 cells are produced.

What is crossing over in meiosis?

The process during Prophase I where homologous chromosomes exchange alleles, increasing genetic variation.

State the number of chromosomes and chromatids at each stage of meiosis in one cell

-Start of with parent cell

46 chromatids so 23 chromosomes

-Interphase

96 chromatids so 46 chromosomes

-Anaphase 1

46 chromatids so 23 chromosomes

-Telophase II

23 Chromatids so 23 chromosomes

What are the three ways in which the process of meiosis increase gentic diversity?

Crossing over of Chromatids/recombination

Independent assortment/ random assortment

Random fertilisation

What is crossing over/recombination?

Occurs during prophase I of meiosis

The homologous chromosomes condense and pair up

The chromatids of each chromosome then twist around one another, forming a chiasmata

What is the effect of a crossing over?

This swaps alleles between the homologous chromosomes to produce different combinations on each chromosome

Each cell has a different chromatid (and different set of alleles), increasing the genetic variation of the offspring

What is independent assortment?

The random arrangement of homologous chromosomes during Metaphase I and II, leading to genetic diversity.

What is the effect of independent assortment?

it is completely random as a result which chromosomes end up in each daughter cell is also random

How do you calculate the possible number of different combinations of chromosomes follwing meiosis, without crossing over?

2 to the power of n

n is the number of homologous chromosome pairs

How does random fertilization contribute to genetic variation?

It is random which male gamete fertilizes which female gamete, leading to diverse offspring.

What is non-disjunction?

A mutation during meiosis where chromosomes fail to separate properly, leading to gametes with abnormal chromosome numbers because one daughter cell may have two copies of a chromosome whereas another may be missing a chromosome

What disorder can result from non-disjunction during meiosis and how does it occur?

Down syndrome, which occurs when there are three copies of a chromosome.

What are the final products of meiosis?

Four haploid cells, each with 23 chromosomes that are genetically different

What is the role of spindle fibers during meiosis?

They help in the movement and separation of chromosomes during anaphase I and II

What is the difference between diploid and haploid cells?

Diploid cells have two sets of chromosomes (2n), while haploid cells have one set (n).

What is a chiasmata?

The point where chromatids twist around each other during crossing over in Prophase I.