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ANSWERS & MARK SCHEMES
QUESTIONSHEET 1
FEATURE MITOSIS MEIOSIS
Involves two successive nuclear divisions 7 3 Does not occur in a haploid cell 7 3 Involves synapsis forming bivalents 7 3 Involves chiasmata formation 7 3 Leads to random assortment of chromatids 7 3 Leads to random assortment of chromosomes 7 3 Occurs during gamete formation in a mammal 3 3 Daughter nuclei have identical genetic content 3 7 DNA replicates before cell division commences 3 3 Involves two chromosomal replications 7 7
TOTAL 10
QUESTIONSHEET 2
- random assortment of chromosomes in Anaphase I; produces new combinations of chromosomes and the genes/alleles they carry from each homologous pair; resulting nuclei thus have new combinations of the genes/alleles present; 3
- random assortment of chromatids during Anaphase II; produces new combinations of alleles in the regrouped chromatids; resulting nuclei thus have new combinations of the alleles present; 3
- chiasmata form between chromatids of different but homologous chromosomes; thus moving alleles from chromosome to chromosome into new combinations; thus modifying the linkage groups present; 3
TOTAL 9
QUESTIONSHEET 3
(a) B A C; A= anaphase, B = prophase, C = telophase; 2
(b) Structure: chromosomes would be replicated into chromatids; chiasmata would be showing between chromatids of homologous chromosomes;
Arrangement: chromosomes would be arranged into homologous pairs; with centromeres attached to the opposite spindles; 4
(c) (i) 2; (ii) 4; (iii) 6; 3
TOTAL 9
ANSWERS & MARK SCHEMES
QUESTIONSHEET 4
(a) in animals consists of a furrowing/tucking in of the cell membrane; eventually separating two nuclei by constriction (of cytoplasm); in plants a cell plate/ middle lamella is synthesised between nuclei; calcium /magnesium pectate/cellulose secreted to form new cell wall; 4
(b) centromere in chromosome holds chromatids together; provides attachment to spindle during cell division; centriole is made of microtubules (in animal cells); forms spindle during cell division; 4
(c) synapsis is pairing of homologous chromosomes; in zygotene/early prophase of meiosis; chiasmata formation occurs in diakinesis/late prophase of meiosis; is cross over of genetic material between chromatids of homologous chromosomes; 4
TOTAL 12
QUESTIONSHEET 5
(a) DNA double helix unwinds to give single stranded (primer) DNA; upon which the complementary strand is assembled; from surrounding nucleotides; forming double stranded daughter DNA; thus each new DNA has one strand from parent DNA and one new strand; max 4
(b) genes consist of alleles at corresponding loci on homologous chromosomes; all alleles on a particular chromosome/chromatid must be carried together during inheritance; chiasmata will swap some of these alleles with those on the sister chromosome; thus the allelic make up of the linkage groups is modified; 4
(c) meiosis reduces two sets of chromosomes to one set/diploid state to haploid state; fertilisation joins two haploid nuclei together restoring the diploid state; 2
TOTAL 10
QUESTIONSHEET 6
(a) A = chromatid; B = spindle fibre; C = centriole; D = centromere; E = chiasma; 5
(b) (i) mitosis; (ii) metaphase; (iii) meiosis; (iv) early anaphase I; 4
(c) cell 2; it is purely random which chromosomes of the homologous pairs go to a particular pole; thus groups of alleles/linkage groups are mixed up in random fashion; giving continuous variation; 3
(d) will mix up alleles between linkage groups into new combinations; giving (more) variation; 2
TOTAL 14
ANSWERS & MARK SCHEMES
QUESTIONSHEET 10
(a) 6 chromosomes in a row on equator; same morphology of chromosomes as in metaphase 1 of meiosis diagram; quality and clarity of diagram; (chromosomes can be in any order but must not be paired or show chiasmata) 3
(b)
Any two of the labels (reject chiasmata) - 2 marks;; chromosomes correctly segregating to poles (in correct order and shape); spindle and completed chiasmata correctly shown; quality and clarity of diagram; (clean, well drawn, joined up lines/ no shading /reasonable size) 5
TOTAL 8
centromere
aster
spindle fibre
chromatids
QUESTIONSHEET 11
(a) mitosis maintains the same chromosome number (reject diploid state since mitosis can take place as haploid to haploid) whereas meiosis halves the chromosome number/reduces the diploid state to the haploid state; mitosis maintains the same genotype whereas meiosis introduces genetic variation; 2
(b) random assortment of chromosomes at Anaphase 1; random assortment of chromatids at Anaphase 2 ; formation of chiasmata; 3
(c) best answered by a genetic diagram, eg.
P Aa × Aa alleles A and a in each parent; (any letters acceptable)
gametes A a A a equal proportions of each gamete; Fl AA Aa Aa aa A is dominant so 3 dominants to 1 recessive; 3
TOTAL 8
QUESTIONSHEET 12
Feature Mitosis Meiosis 1 Meiosis 2 Occurs during gametogenesis √ √ √ ; DNA replicates before prophase √ √ × ; Bivalents form during prophase × √ × ; Chiasmata are formed × √ × ; Chromatids randomly assort during anaphase × × √ ; TOTAL 5
(1 mark per correct line)
do not accept √
