Sexual reproduction and meiosis Flashcards
What is sexual reproduction
the production of new individuals resulting from the joining of 2 specailised cells known as gametes
How is a haploid gamete formed
A nuclei are formed with one set of chromsomes
What are gonad
sex organs in animals
what are antheres
male sex organs in plants
How can male gametes be described
many, mini , motile
How can female gametes be describe
few , fat , fixed
Why is meiosis so important
it reduces the chromosome number in gametes from diploid to haploid, so that SR is possible without each generation carrying an increasing burden of genetic material
What is independent assortment
the chromosomes that came from the individuals parents are distributed into the gametes and so into their offspring completely at random
What is crossing over
large multi enzyme complexes ‘cut and join’ bits of the maternal and paternal chromatids together
What is chiamsata
the points where the chromatids break during recombination
What is the + of crossing over
the exchange of genetic material leads to added gentic variation
What is the - of recombination
errors in the processes leads to mutations
What happens in prophase 1
each chromosome appears in the condensed form with 2 chromatids. Homologous pairs of chromosomes associate with each other (crossing over)
What happens in metapahse 1
the spindle forms and the pairs of chrosomes line up on the metaphase plate
What is anaphase 1
the centromeres do not divide , One chromosome from each homologous pair moves to each end of the cell. As as result of the chromosome number in each cell is half of the original
What happens in telopahse 1
the nuclear membrane re-forms and the cells begin to divide
What happens in prophase 2
new spindles are formed
What happens in metaphase 2
the chrosomes still made up of pairs of chromatids line up in the metaphase plate
What happens in anapahse 2
the centromers now divide and the chromatids move to the opposte ends of the cell
What happens in telophase
nuclear envelopes re-form the chromosomes and return to their interpahse state and cytokensis occurs
Giving 4
daugther cells with half the chromosomes number of the orgianl diploid cell
