Introduction to reproduction Flashcards
1
Q
What is the current trend for fertility?
A
- fertility is decreasing in both humans and animals
2
Q
What factors and reducing fertility?
A
- pollution
- deforestation
- rising global temperatures
3
Q
What do factors that effect fertility lead to?
A
- altered seasonal breeding patterns
- migration disruption
- hormone disruption/sex change
4
Q
What’s happening to male fish?
A
- 1/3 of male fish in UK rivers are feminised due to pollution levels
5
Q
How are marine mammals adversely affected by pollution?
A
- constant exposure to pollutants in water
- pollutants held in large fat stores
- passed into offspring via milk
6
Q
Why is it important to understand reproduction in all species?
A
- can help minimise infertility and help develop treatments/technologies
7
Q
What is biological reproduction?
A
- the process by which new individuals are produced from previously existing individuals
8
Q
What does asexual reproduction mean?
A
- production of individuals that are genetically identical to itself
- offspring produced by mitosis
9
Q
What does sexual reproduction mean?
A
- two individuals produce offspring that have genetic characteristics from both parents involved - meiosis
- this introduces genetic diversity
10
Q
What are the advantages of sexual reproduction?
A
- recombination of maternal and paternal chromosomes in the gamete results in genetic variation amount the offspring
- hybrid vigour
11
Q
What are the disadvantages if sexual reproduction?
A
- two parents are required
- only half of an individuals genes are passed on via meiosis into the germ cells = loss of genetic info
- reproduction rate are less efficient
12
Q
What is a chromosome?
A
- DNA molecule with part or all the genetic material of the organism
- made up of two identical sister chromatids
13
Q
What is a chromatid?
A
- one copy of a newly copied chromosome which is still joined to the original chromosome by a single centromere
14
Q
What is a haploid?
A
- one set of chromosomes in a cell (n)
14
Q
What is ploidy?
A
- number of sets of chromosomes in a cell
15
Q
What is a diploid?
A
- two sets of chromosomes in a cell (2n)
16
Q
What is tetraploid?
A
- 4n
17
Q
What is polyploid?
A
- (n+)
18
Q
What is the haploid (n)?
A
- is the number of chromosomes in a gamete
19
Q
What is the human haploid number?
A
- n = 23 chromosomes
20
Q
Human diploid cells contains how many chromosomes?
A
- 46 chromosomes (23 pairs)
21
Q
What type of cell are most somatic body cells?
A
- diploid (2n)
22
Q
How would a tetraploid be made?
A
- if a diploid sperm were to fertilise a diploid egg, the resulting embryo would be a tetraploid (4n)
23
Q
What is genetic complement of germ cells?
A
- where sperm and egg are haploid
24
How does meiosis generate genetic diversity?
- by creating new combinations of alleles
25
Each homologous set of chromosomes is made up of what?
- 2 homologues
26
Meiosis only occurs during what?
- gamete formation
27
During meiosis there are 2 successive nuclear divisions - what are these called?
- meiosis I
- meiosis II
28
How many rounds DNA replication does meiosis have?
- only one round of DNA replication
29
Describe the process of meiosis?
1. one parental cell gives rise to 4 daughter cells
2. daughter cells have half the number of chromosomes found of the original parent cell
3. crossing over results in the cells being genetically different from each other
30
What is interphase in meiosis I?
- DNA in the cell is copied resulting in 2 full sets of chromosomes
31
What happens during prophase I?
- copied structures condense into x-shaped structures
- each chromosome composed of two sister chromatids containing genetic info
- chromosomes pair so that both copies of each chromosome comes together
- recombination or cross-over may then occur
32
What is recombination or cross over between chromatids?
- two chromosomes seem to join at several points called chiasmata with intention to create genetic diversity and hybrid vigour
33
What is the chiasmata the site of?
- the site of gene exchange
34
What is homologous recombination?
- exchange of identical DNA sequences between similar or identical DNA molecules
35
Homologous recombination involves the formation of what?
- involves the formation of synapsis of homologous chromosomes
36
Describe the process of homologous recombination?
- doubled stand break form in both DNA molecules
- DNA strands are exchanged, and double-strand breaks are repaired
= crossing over
37
What is the synapsis and recombination process mediated by?
- synaptonemal complex
38
What is chiasma?
- sites of crossing over
39
What happens in metaphase I?
- homologous chromosomes align at the equatorial plate
40
What happens at anaphase I?
- homologous pairs separate with sister chromatids remaining together
41
What happens during telophase I?
- two daughter cells are formed with each daughter cell containing only one chromosome of the homologous pair
42
What is meiosis II?
- gamete formation
43
What happens during prophase II?
- DNA does not replicate
44
What happens during metaphase II?
- chromosomes align at the equatorial plate
45
What happens at anaphase II?
- centromeres divide, and sister chromatids migrate separately to each pole
46
What happens in telophase II?
- cell division is complete
- four haploid cells are obtained
47
In meiosis II in a female what then happens to the 4 haploid cells?
- Only one cell will go on to form the ovum
- the other 3 go on to form polar bodies that will store genetic material which is important to provide nutrition and support primary ovum
48
In meiosis II in males what happens to the 4 haploid cells produced?
- all cells are viable to form sperm cells
49
Spermatogonia undergo mitosis first to provide and do what?
- to provide a stock of cells for spermatogenesis
- and replace themselves
50
Some spermatogonia then enter meiosis forming what?
- forming spermatocytes (2n)
51
Spermatocytes undergo two rounds of division forming what?
- haploid spermatids
52
Spermatids differentiate further into what?
- spermatozoa
53
Once initiated spermatogenic cells progress through meiosis how?
- without stopping
- unless errors in chromosome number or recombination detected
54
How do oogonia provide a stock of egg precursors?
- oogonia expand by mitosis during foetal development to provide a stock of egg precursors
55
Once oogonia eventually enter meiosis what do they become?
- primary oocytes
56
Oocytes start meiosis but arrest where and remain here until when?
- Arrest in prophase I before completing first division and remain in this arrested state until puberty
57
Oocytes remain arrested until just before ovulation then re-enter meiosis but arrest again where until when?
- arrest in metaphase II until fertilisation
58
What is non-disjunction?
- failure of homologous chromosomes or sister chromatids to separate during meiosis
59
What does non-disjunction result in?
- results in the production of zygotes with abnormal chromosome numbers
60
Non-disjunction occurs in two ways - what are these?
* monosomy - absence of one chromosome
* Trisomy - additional chromosome
61
Name some common non-disjunction disorders?
* Down's syndrome - Trisomy 21
* Turner's syndrome - monosomy 23 (XX)
* Kleinfelter’s Syndrome – Trisomy 23 (XXY)
* Edward's syndrome - Trisomy 18
62
Can non-disjunction occur in both meiosis I and II?
- yes
63
What is a karyotype?
- picture of an individual's chromosomes
64
You can have trisomy in cows and horses - where are these found?
- Trisomy 27 in horses
- Trisomy 28 in cattle
