meiosis and genetic variation Flashcards
explain what’s meant by fertilisation .
- sexual reproduction = nucleus of sperm cell fuses with mucous of egg cell —> fusion of nuclei
what is a mutation?
- change/ alteration to the DNA base sequence.
- often arise spontaneously during DNA replication
—> may result in altered primary structure (determines later stages of folding so result in change of overall 3D structure)
what is a substitution mutation?
- when nucleotide in DNA sequence is replaced by another = more likely to be quiet mutation .
- no change occurs in amino acid sequence (genetic code is degenerate)
- TGCCTA —> TGACTA
what is a deletion mutation?
- when one or more bases is removed (nucleotide in DNA sequence lost)
- change codon at the point of mutation, and leads to a frame shift meaning the entire amino acid sequence will be diff
- TGCCTA —> TGCTA
explain what’s meant by insertion mutation
- one of more bases added
- e.g = TGCCTA —> TGCCCTA
- change the codon and all following codons
what is a inversion mutation ?
a sequence of bases is reversed
- TGCCTA —> TGCATC
- result in a change to a single amino acid
what is a mutagenic agent ? give examples
- factors that increase rate of gene mutation
- x-rays, UV light, gamma rays , certain chemicals (in alcohol + tobacco)
what is a polyploidy chromosome mutation?
- where individual has 3 or more sets of chromosomes instead of 2
what is chromosome non-disjunction?
- when chromosomes fail to separate correctly in meiosis, results in gametes with one more or less chromosome than normal
what is meiosis?
- form of cell division that produces 4 genetically diff haploid cells - known as gametes .
- involves 2 rounds of cell division = meiosis I and II
how does meiosis differ from mitosis?
- meiosis produces 4 genetically diff cells with half the no. chromosomes as parent cells
- mitosis = produces 2 genetically identical cells with same no. chromosomes as parent cells
what happens during meiosis I
1) interphase ; DNA replicates so now 2 identical copies of each chromosome (chromatids )
2) prophase I = chromatids condense + arrange themselves into homologous pairs (bivalents) —> crossing over occurs
- nuclear envelope disintegrates + spindle fibres form
3) metaphase I = homologous chromosomes line up along equator + attach to spindle fibres by centromeres
4) anaphase I = humorous chromosomes separated
5) telophase I = chromosomes reach opposite pole of cell = nuclear envelope reforms around chromosomes
= cytokinesis results formation 2 daughter cells
what happens during meiosis II?
1) prophase II = chromosomes condense , nuclear envelope disintegrates + spindle fibres form
2) metaphase II = chromosomes attach to spindle fibres by centromeres
3) anaphase II = sister chromatids are separated
4) telophase II = chromatids reach opposite poles of cell + cytokineses takes place = 4 genetically unique daughter cells produced
give 2 ways meiosis produced genetic variation?
1) crossing over during meiosis I
2) independent assortment (random segregation) of homologous chromosomes + sister chromatids
—> result in new combination of alleles
explain the process of crossing over
- during prophase I
- homologous chromosomes move toward each other + exchange genetic material
- chromatid from maternal chromosome becomes twisted around paternal chromosome + connect thru chiasmata
- pieces chromosomes exchanged + chromatids seperate = form chromosomes with diff combinations of alleles
