Introduction to reproduction Flashcards
What is the current trend for fertility?
- fertility is decreasing in both humans and animals
What factors and reducing fertility?
- pollution
- deforestation
- rising global temperatures
What do factors that effect fertility lead to?
- altered seasonal breeding patterns
- migration disruption
- hormone disruption/sex change
What’s happening to male fish?
- 1/3 of male fish in UK rivers are feminised due to pollution levels
How are marine mammals adversely affected by pollution?
- constant exposure to pollutants in water
- pollutants held in large fat stores
- passed into offspring via milk
Why is it important to understand reproduction in all species?
- can help minimise infertility and help develop treatments/technologies
What is biological reproduction?
- the process by which new individuals are produced from previously existing individuals
What does asexual reproduction mean?
- production of individuals that are genetically identical to itself
- offspring produced by mitosis
What does sexual reproduction mean?
- two individuals produce offspring that have genetic characteristics from both parents involved - meiosis
- this introduces genetic diversity
What are the advantages of sexual reproduction?
- recombination of maternal and paternal chromosomes in the gamete results in genetic variation amount the offspring
- hybrid vigour
What are the disadvantages if sexual reproduction?
- 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
What is a chromosome?
- DNA molecule with part or all the genetic material of the organism
- made up of two identical sister chromatids
What is a chromatid?
- one copy of a newly copied chromosome which is still joined to the original chromosome by a single centromere
What is a haploid?
- one set of chromosomes in a cell (n)
What is ploidy?
- number of sets of chromosomes in a cell
What is a diploid?
- two sets of chromosomes in a cell (2n)
What is tetraploid?
- 4n
What is polyploid?
- (n+)
What is the haploid (n)?
- is the number of chromosomes in a gamete
What is the human haploid number?
- n = 23 chromosomes
Human diploid cells contains how many chromosomes?
- 46 chromosomes (23 pairs)
What type of cell are most somatic body cells?
- diploid (2n)
How would a tetraploid be made?
- if a diploid sperm were to fertilise a diploid egg, the resulting embryo would be a tetraploid (4n)
What is genetic complement of germ cells?
- where sperm and egg are haploid
How does meiosis generate genetic diversity?
- by creating new combinations of alleles
Each homologous set of chromosomes is made up of what?
- 2 homologues
Meiosis only occurs during what?
- gamete formation
During meiosis there are 2 successive nuclear divisions - what are these called?
- meiosis I
- meiosis II
How many rounds DNA replication does meiosis have?
- only one round of DNA replication
Describe the process of meiosis?
- one parental cell gives rise to 4 daughter cells
- daughter cells have half the number of chromosomes found of the original parent cell
- crossing over results in the cells being genetically different from each other
What is interphase in meiosis I?
- DNA in the cell is copied resulting in 2 full sets of chromosomes
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
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
What is the chiasmata the site of?
- the site of gene exchange
What is homologous recombination?
- exchange of identical DNA sequences between similar or identical DNA molecules
Homologous recombination involves the formation of what?
- involves the formation of synapsis of homologous chromosomes
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
What is the synapsis and recombination process mediated by?
- synaptonemal complex
What is chiasma?
- sites of crossing over
What happens in metaphase I?
- homologous chromosomes align at the equatorial plate
What happens at anaphase I?
- homologous pairs separate with sister chromatids remaining together
What happens during telophase I?
- two daughter cells are formed with each daughter cell containing only one chromosome of the homologous pair
What is meiosis II?
- gamete formation
What happens during prophase II?
- DNA does not replicate
What happens during metaphase II?
- chromosomes align at the equatorial plate
What happens at anaphase II?
- centromeres divide, and sister chromatids migrate separately to each pole
What happens in telophase II?
- cell division is complete
- four haploid cells are obtained
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
In meiosis II in males what happens to the 4 haploid cells produced?
- all cells are viable to form sperm cells
Spermatogonia undergo mitosis first to provide and do what?
- to provide a stock of cells for spermatogenesis
- and replace themselves
Some spermatogonia then enter meiosis forming what?
- forming spermatocytes (2n)
Spermatocytes undergo two rounds of division forming what?
- haploid spermatids
Spermatids differentiate further into what?
- spermatozoa
Once initiated spermatogenic cells progress through meiosis how?
- without stopping
- unless errors in chromosome number or recombination detected
How do oogonia provide a stock of egg precursors?
- oogonia expand by mitosis during foetal development to provide a stock of egg precursors
Once oogonia eventually enter meiosis what do they become?
- primary oocytes
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
Oocytes remain arrested until just before ovulation then re-enter meiosis but arrest again where until when?
- arrest in metaphase II until fertilisation
What is non-disjunction?
- failure of homologous chromosomes or sister chromatids to separate during meiosis
What does non-disjunction result in?
- results in the production of zygotes with abnormal chromosome numbers
Non-disjunction occurs in two ways - what are these?
- monosomy - absence of one chromosome
- Trisomy - additional chromosome
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
Can non-disjunction occur in both meiosis I and II?
- yes
What is a karyotype?
- picture of an individual’s chromosomes
You can have trisomy in cows and horses - where are these found?
- Trisomy 27 in horses
- Trisomy 28 in cattle
