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3.9 (i) o what is gene loci
gene: short length of DNA that codes for 1 polypeptide chain
- loci: position of a gene on a chromosome
- chromosomes contain different genes = code different proteins = each specific gene occupies a specific locus
3.9 (ii) o what are the types of linkages on a chromosome
sex-linked: gene located on a sex chromosome
- autosomal-linked: gene located on a body chromosome that's not a sex chromosome
3.9 o (ii) why are males more affected by sex linkage
2 sex chromosomes = X + Y
- majority of sex linkages are X-chromosome = ♂ XY = 1 X = higher chance of sex-linked recessive conditions > ♀
3.9 o (ii) why are females less affected by sex linkage
2 sex chromosomes = X + Y
- ♀ XX = have 2 X = likely have dominant allele = masks recessive allele = heterozygous/carrier of sex-linked disease
3.10 what is meiosis
meiosis: process of nuclear division of producing 4 daughter cells (sex gametes)
3.10 what happens during prophase 1 of meiosis
chromosomes condense = crossing-over occurs
- nuclear envelope breaks down + homologus pairs associate
3.10 what happens during metaphase 1 of meiosis
spindle fibres emerge from centrosomes = chromosomes line up on the metaphase plate
3.10 what happens during anaphase 1 of meiosis
1 chromosome per homologus pair moves to opposite poles of cell = centromeres don't divide
- chromosome number per cell goes from diploid → haploid
3.10 what happens during telophase 1 of meiosis
nuclear membrane reforms + allows cell to divide
- some cells continue cytokinesis = brief interphase = no DNA replication
3.10 what happens during prophase 2 of meiosis
new spindle fibres form
3.10 what happens during metaphase 2 of meiosis
chromosomes still made up chromatids = lines up along metaphase plate
3.10 what happens during anaphase 2 of meiosis
centromeres divide = chromatids separate + move to opposite poles of cells
3.10 what happens during telophase 2 of meiosis
nuclear envelopes reform = chromosomes enter interphase + cytokinesis
- produces 4 daughter cells with haploid number
3.10 what is crossing over (recombination)
crossing over: process where large multi-enzyme complexs cut + rejoin materal + paternal chromatids
- genetic material exchange causes genetic variation
3.10 what is independent assortment
independent assortment: process where chromosomes of male + female gamates distributed randomly
- different combination of chromosomes in daughter cells = increase genetic variation
3.12 how does fertilisation occur in mammals
sexual intercourse = semen ejaculated in vagina near cervix
- sperm travels oviduct via chemical trial released from egg
- fertilisation occurs when sperm + egg meet
3.11 how is the egg cell specialised to its function
egg cell: sex female gamete
- large cell = contains food = nourishs embryo
- follicle cells = protective layer = forms 'zona pellucida' = glycolipid layer = prevents polyspermy
3.11 how is the sperm cell specialised to its function
sperm cell: sex male gamete
- mitochondria = provides ATP for movement
- flagellum = allows the sperm to move
- acrosome = digestive enzyme = break down zona pellucida to penetrate + fertilise egg
3.12 what is fertilisation
fertilisation: fusion of male gamete's nuclei + female gamete's nuclei = forms zygote = 46 chromosomes = 23♂ + 23♀
- zygote → embryo via mitosis = cells become specialised + form specific functions
3.14 what is mitosis
mitosis: process of nuclear division producing 2 genetically identical daughter cells
3.12 what is the acrosome reaction
head of sperm (acrosome) has digestive enzymes = breaks down zona pellucida
- allows sperm to penetrate egg's membrane + fertilise
3.12 what is the cortical reaction
egg release vesicles (cortical granules) between egg cell membrane + zona pellucida
- chemicals in cortical granules = zona pellucida harden = preventing polyspermy
3.14 describe the structure of a chromosome
chromosome = has 2 identical chromatids = joined together by the centromere
- each chromatid contains 1 molecule of DNA
3.14 what happens during prophase 1 of mitosis
chromosomes condense = 2 centrosomes replicated = move to opposite poles
- spindle fibres emerge from centrosomes = nuclear envelope breaks down
3.14 what happens during metaphase 1 of mitosis
centrosomes reach opposite pole = spindle fibres extends + attachs per chromatid from opposite pole
- chromosomes line up at the metaphase plate
3.14 what happens during anaphase 1 of mitosis
sister chromatids separated at centromere → chromosome
- chromosomes pulled opposite pole via spindle fibre shortening
3.14 what happens during telophase 1 of mitosis
chromosomes brought at opposite poles + decondense
- nuclear envelope reforms = spindle fibres break down
3.14 why is mitosis crucial for biological processes
growth of multicellular organisms, replacement/repairment of cells + asexual reproduction
- genetically identical cells = replacing damaged tissues/limbs = cells can specialise
3.14 what is the cell cycle
cell cycle: regulated sequence of events between cell divison
- interphase, nuclear division + cytokinesis = length of cycle varies between environmental factors
3.14 what occurs in interphase (G1, S + G2)
old cell division + S phase = G1 phase
- G1 = replicate organelles/enzymes = signal tell cell divide = DNA in nucleus replicate = S phase
S phase + new cell division = G2 phase
- G2 = cell grows + new DNA synthesised = checks errors
3.16 what is mitotic indices
mitotic index = number of cells in mitosis/total cell in sample
3.14 what occurs in nuclear division (mitosis)
follows interphase = cell growth stops
- 2 identical chromatids separate = ensures new nucleus has same genetic information as original nucleus
3.14 what occurs in cytokinesis
follows M (mitosis) phase
- whole cell divides = 1 nucleus moves into each cell = 2 daughter cells