Mitosis And Meiosis Flashcards
What disease is due to trisomy of chromosome 21?
Down syndrome
Outline the structure of a chromosome
p (short) +q (long) arm
Telomere at end of chromosomes
What are the locations of centromeres?
metacentric - centre
submetacentric - between top and middle
acrocentric - closer to top (1 very short + 1 very long arm)
telocentric - very end
What are telomeres, what is their function and where are they found?
- DNA sequence - TTAGGG
- Protect chromosomes from degradation + limit the number of times mitosis occurs
- Ends of chromosomes
What condition is caused by one X chromosome missing?
Turner syndrome
Outline karyotyping
- method of describing chromosome composition
- chromosome number , gender + mutations
e.g.
46,XX - normal female
47,XY,+21- male with trisomy 21 (downs)
What are the phases of mitosis?
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
What happens in prophase?
- chromosomes condense
- spindle fibres develop
What happens in prometaphase?
- nuclear envelope + nucleolus dissolves
- spindle fibres attach to centromere
What happens in metaphase?
Chromosomes align at centre
What happens in anaphase?
Sister chromatids pulled to opposite poles
What happens in telophase?
- nuclear envelope reforms
- cytoplasm starts to cleave (splitting in cytokinesis)
What is non-disjunction?
Name a condition that occurs from this
Failure of one or more pairs of sister chromatids to separate normally»_space; gain/loss of a chromosome
Down syndrome - trisomy of chromosome 21
Stages of meiosis
Meiosis I - same as mitosis
Meiosis II - same step occur without DNA replication
- chromosomes separate to form chromatids
- four haploid daughter cells
What is aneuploidy?
What is it caused by?
- Condition of having an abnormal number of chromosomes in a haploid organism
- Caused by non-disjunction in mitosis or meiosis
How does meiosis create genetic diversity?
- crossing over
- independent assortment
- random segregation
What is crossing over?
When does it occur?
- Exchange of regions of DNA at the chiasmata between 2 homologous chromosomes due to twisting
- Occurs in meiosis I
What is a chiasmata?
Point at which crossing over of chromosomes occurs in meiosis
What is independent assortment?
The random organisation of chromosomes along the midline of the cell
What is random segregation?
Random distribution of alleles among the 4 gametes
Outline spermatogenesis
- 1 spermocyte (2n) > 4 mature sperm (n)
- over 60 days
Outline oogenesis
- 1 oocyte (2n) > 1 egg (n) + 3 polar bodies
- over 12-50 years
Impact of missegregation in meiosis
- infertility
- miscarriage
- mental retardation
What is the karyotype of Turner’s syndrome?
45, XO
