Bs1050- mitosis and meiosis

What does mitosis produce vs meiosis

2 Diploid, identical genetic information

Meiosis- haploid, variable genetic information

Mitosis stages (interphase)

Mitosis steps

prophase, metaphase, anaphase, telophase

Prophase

Spindle fibers appear, chromosomes condense

Prometaphase

Spindle fibres attach to chromosomes

Chromosomes condense

Metaphase

Chromosomes align

Anaphase

Centromeres divide, sister chromatids move to opposite poles

Telophase

Nuclear membrane reforms, chromosomes decondense

Spindle fibres disappear

Meiosis I

Prophase 1- chromosomes begin to condense, homologous chromosomes pair, crossing over occurs, recombinant chromosomes

Metaphase I- spindle fibres attach to chromosomes, chromosomes line up in the centre of the cell

Anaphase 1- chromosomes start to move to opposite ends of a cell as spindle fibres shorten

Telophase 1- chromosomes reach opposite ends nuclear membrane forms

Meiosis II- males

Prophase II- chromosomes begin to condense nuclear membrane dissolves spindle fibres form

Metaphase II- spindle fibres attach to chromosomes chromosomes line up in the center of the cell Anaphase

Anaphase II- centromeres divide and sister chromatids move to opposite ends of cell as spindle fibres shorten Telophase

Telophase II- chromosomes reach opposite ends nuclear membrane forms

Cytokinesis- cell division occurs

Meiosis in females

At the end of meiosis I- telophase makes 1 polar body, 1 egg cell precursor

Meiosis 2- egg cell splits into 2 as well into a polar body and MATURE egg cell

Key features of meiosis

Replication precedes division

-Two sequential divisions

-Meiosis I (Reductional) (chromosome number is halved)

o Homologous chromosomes pair up

o Formation of chiasmata; these are essential for

chromosome segregation(points where Homochromo cross over)

o Homologous chromosomes separate ( 2n->n)

-Meiosis II (Equational) (chromosome number stays the same)(because sister chromatids separate)

o Division of centromeres and separation

of sister chromatids

-Events in Meiosis I and II differ; both differ from mitosis

Key feature s

Genetic diversity [production of new combinations of

genes different from those of each parent] through

recombination

by the random segregation of maternal and paternal chromosomes in Meiosis I

by the exchange of genetic material between homologous chromosomes during Meiosis I

Lecture 2

What was mendels approach

Model system based

Reductionist

Quantitative

Mendel first law

Allele segregation

-in a diploid the two copies of a gene segregate at meiosis

- 2 get 4 diff results you need to have 2 events (generations)

Genotypic ratio

R+R+, R+ r-, r- R+, r-r- = 1:2:1

Phenotypic

3 R+ and 1 fully r- so 3:1

Second law

Independant assortment- dihybrid cross

During gamete formation alleles of Independant genes assortment randomly

Members of different chromosome pairs assortment randomly at meiosis

Interpretaion of 9:3:3:1

From the first law we know that the fusion of two gametes (two

events) each carrying one of two possible alleles at one locus (two

outcomes) gives 4 possible results.

2^2 = 4

Therefore 16 possible results must derive from the two gametes (two events) carrying one of two alleles (two outcomes) at two loci

2^2 x 2^2 = 16