sexual reproduction Flashcards
briefly summarise how sexual reproduction works?
- two parents (1 male, 1 female)
- each parent produces haploid gametes
- via meiosis
- a male and female gamete fuse via fertilisation
- produces diploid zygote
what are the advantages of sexual reproduction?
- produces offspring with genetic variation
- members of a species have advantageous alleles to survive new threats
- so clones are more vulnerable
XX chromosomes
female
XY chromsomes
male
what are autosomes?
pairs of chromosomes that are not sex chromosomes
define haploid chromosome
- contains 1 set of chromosomes
- 23
- 1 member of each homologous pair
define gamete
- sex cells
- male = sperm
- female = egg
what is the product of sexual reproduction in a flowering plant?
seed
what are some advantages of asexual reproduction over sexual reproduction?
- colonise a stable environment quickly
- don’t need to find a mate
which 3 processes lead to increased genetic variation during meiosis?
- crossing over
- independent assortment
- random fertilisation
when does crossing over occur?
prophase 1
what happens during crossing over?
chromatids twist around and swap alleles
how does crossing over increase genetic variation?
new combinations of alleles occur
- more phenotypes expressed
- respond to natural selection under threat
when does independent assortment of paired chromosomes occur?
metaphase 1
what happens during independent assortment of paired chromosomes?
- bivalents line up on cell equator
- different combinations of chromosomes in each daughter cell of first division
how does independent assortment of paired chromosomes increase genetic variation?
there are new chromosome combinations in each daughter cell of the first division
when does independent assortment of single chromosomes occur?
metaphase 2
what happens during independent assortment of single chromosomes?
each replicated chromosome aligns in an independent position
how does independent assortment of single chromosomes increase genetic variation?
creates unique chromatid combinations of each daughter cell of the second division
what is random fertilisation?
any sperm fertilises with any egg
how does random fertilisation increase genetic variation?
each individual is completely unique
how do you calculate the possibilities of gametes produced by one parent?
2 to the power of the haploid number
how do you calculate the possibilities of combinations produced by sexual reproduction?
2 to the power of the haploid number squared
outline the events that lead to genetic variation in gametes (5)
- meiosis
- mutation = random
- crossing over of chromatids, swapping alleles in prophase 1 creating new allele combinations
- independent assortment in metaphase 1&2 - bivalents line up in middle of cell and new chromosome combinations form
- random fertilisation - offspring is completely unique
