Lecture 3 and 4 Flashcards
What aneuploidy occurs in down syndrome?
Extra chromosome 21
What is non-disjunction?
The failure of homologous chromosomes to separate properly during cell division
What are the 4 types of centromere position?
Metacentric (centre)
Submetacentric (offset from centre)
Acrocentric (severely offset)
Telocentric (at the very end)
What are the names given to the different length arms of a chromosome on either side of a centromere?
p arm (Short) q arm (long)
How long is M phase in humans?
2 hours
How long is G1 in humans?
11 hours
How long is S phase in humans?
7 hours
How long is G2 in humans?
4 hours
What are the stages of the cell cycle?
Prophase, metaphase, anaphase, telophase, interphase
What happens during prophase?
Chromosomes condense and thicken, appear as identical sister chromatids, mitotic spindle starts to form
What is the structure of the kinetochore?
Inner plate, middle layer, outer plate, kinetochore microtubules
What happens during prometaphase?
Nuclear envelope fragments
Centrosomes move to opposite ends
Spindle fibres attach at kinetochore
What happens during metaphase?
Sister chromatids aline along metaphase plate
What triggers anaphase?
Separase
How does separase trigger anaphase?
Hydrolyses cohesin
What happens during anaphase?
Spindle fibres contract
Pull sister chromatids apart
Daughter chromosomes at each pole
What happens during telophase?
Nuclear envelopes begin to reform, nucleoli reappear
Chromosomes decondense
When does cytokinesis begin?
Anaphase
When does cytokinesis end?
After telophase
How do animal cells achieve cytokinesis?
Contractile ring pinches cell into equal halves
How do plants achieve cytokinesis?
Membrane enclosed disk (cell plate) forms inside cell near equator
What is an animal cell containing two or more nuceli known as?
Syncytium
What is multinucleate plant tissue known as?
Coenocyte
What is a disadvantage of sexual reproduction?
Only half the genes are transmitted from each parent (less efficient to pass on genome)
What is oogenesis?
Asymmetrical meiotic division to produce one large ovum
What is spermatogenesis?
Symmetrical meiotic division to produce 4 sperm
When does oogenesis begin?
In the fetus
What is the first step of oogenesis?
Diploid germ cells, oogonia, multiply by mitosis
What do oogonia produce?
Primary oocytes, which under go meiosis
What happens when primary oocytes undergo meiosis?
Asymmetric division. Division is suspended at diplotene in fetus, not completed until ovulation
What is the product of meiosis I of primary oocytes?
Secondary oocyte (larger) First polar body (smaller)
What happens during meiosis II of the secondary oocyte?
Undergoes asymmetric division: haploid ovum and second polar body, then stops meiosis
When does the meiosis II occur?
Fertilization
What are male germ cells?
Spermatogonia
Where does spermatogenesis occur?
Testes
What does mitotic divisions of spermatogonia produce?
Diploid cells, primary spermatocytes
What happens when primary spermatocytes undergo symmetrical meiotic divisions?
Produce secondary spermatocytes
What happens to secondary spermatocytes at puberty?
Symmetrical meiosis II, produces spermatids
What happens to spermatids?
Differentiate into sperm
What are the stages of prophase I of meiosis?
Leptotene Zygotene Pachtene Diplotene Diakinesis (Loser Zoos Put Down Dogs)
What happens during leptotene?
Chromosomes thicken
What happens during zygotene?
Chromosomes seek homologous partners,
Synapsis
What is the zipper that holds together homologous partners during synapsis?
Synaptonemal complex
What happens during pachytene?
Recombination- exchange parts between non-sister chromosomes (crossing over)
What are synapsed chromosomes known as?
Bivalent (two chromosomes) or tetrad (4 chromatids)
What happens during diplotene?
Zipper complex dissolves
Homologous chromosomes remain merged at chiasmata
What are chiasmata?
Regions where crossing-over occured
What happens during diakinesis?
Further condensation
Nuclear envelope breaks down, spindle begins to from
What happens during interkinesis of meiosis I?
Chromosomes decondense, sometimes stay condensed. There is no S phase.
What happens during meisosis II?
Sister chromatids separate to produce haploid gametes
At the end of meisosis II, each daughter cell has the same number of chromosomes as the parental cell. Thus meisosis is termed a _______________
Equational division
When does nondisjunction occur?
When homologs of chromosome pairs do not segregate during meiosis I
Who determined X and Y chromosomes determine sex?
Walter S. Sutton
How did Walter S. Sutton determine X and Y chromosomes determine sex?
Followed meiotic divisions of cells from testes of great lubber grass hoppers- 2 chromosomes are unmatched
What does not occur in mitosis that does in meiosis?
Synapsis
Crossing over
Name 4 mistakes that can occur during cell division
Deletion, translocation, inversion, non-disjunction
Name a disease associated with deletions.
Cri-du-chat syndrome (del(5p))
Name a disease associated with translocation.
Charcot-Marie-Tooth disease type 1A (dup of portion of (p17)
Name a disease associated with inversion.
(pX) implicated in mucopolysaccharidosis type II (Hunter syndrome)
Name a disease associated with non-disjunction
Turner syndrome (X missing)
What trisomy is edward syndrome?
18
What trisomy is patau syndrome?
13
What are some characteristics of edward syndrome?
Mental/physical retardation
Facial abnormalities
Extreme muscle tone
Early death
What are some characteristics of patau syndrome?
Mental/physical retardation
Organ defects
Large triangular nose
Early death
Name two ways chromosomal alterations can be diagnosed prentally.
Amniocentesis
Chorionic ic villi sampling
What is amniocentesis?
Fetal cells are obtained from amniotic fluid
What is chorionic villi sampling?
Fetal cells are obtained from the chorion (fetal part of the placenta)
What three genetic processes can lead to genetic varation?
Recombination, aneuploidy, polyploidy
