topic 2 : cells, viruses and reproduction of living things Flashcards

Question

how is there variation in meiosis (3 ways)

Answer 1

- crossing over of homologus pairs : exchange of genetic information - recombination of alleles - independent assortment of chromosomes : lined up and pulled randomly

Answer 2

- provides genetic variation by crossing over - independent assortment - it halves the chromosome numbers - produces haploid cells so diploid number restored during fertilisation

Answer 3

- growth and repair - asexual reproduction

Answer 4

change in base sequence of DNA

Answer 5

* Duplication – an extra chromosome * Deletion – a section of a chromosome is removed * Translocation – one part of a chromosome detaches and reattaches to another chromosome * Inversion – one part of the chromosome is flipped * Non-disjunction – homologous chromosomes or the chromatids fail to separate

Answer 6

* Insertion of a base – frameshift mutation. The earlier the insertion, the greater the change in the protein * Deletion of a base – frameshift mutation * Replacement of a base Only one amino acid will be affected

Answer 7

- homologus chromosomes may not separate in anaphase 1 - or sister chromatids may fail to separate in anaphase 2 - gametes may end up with an estra chromosome or none at all when these fertilise with normal gametes the zygote has either one extra chromosome (polysomy) or one mising chromosome (monosomy)

Answer 8

polysomy/non-disjunction

Answer 9

- non - disjunction of chromosome 21 --> zygote has 3 copies of chromosome 21 - this is trisomy of chromosome 21, leading to down's syndrome which affects mental and physical development eg. down's syndrome

Answer 10

- non-disjunction of the sex (X and Y) chromosomes eg. turner's syndrome : in females who are missing an X chromosome, this causes infertility and they cannot mature without sex hormone treatment

Answer 11

- start with primordial gem cell - go through mitosis several times to form spermatogonia - growth of spermatogonia to form primary spermatocyte - primary spermatocyte goes through meiosis 1 to form secondary spermatocyte - secondary spermatocyte goes trhough meiosis 2 to form spermatids - these undergo differentiation to form mature spermatozoa

Answer 12

- start with primordial germ cell - go through mitosis several times to form oogonia - forms other oogonia but they become degenerate and do not divide - the generate oogonia goes through meiosis 1 to form a secondary oocyte and a polar body (does not develop into gamete) - the secondary oocyte goes through meiosis

Answer 13

* Zona pellucida: protective layer that the sperm has to penetrate – it prevents polyspermy (prevents multiple sperm fertilising the egg) * Cortical granules release substances to cause the zona pellucida to harden * The nucleus is haploid (in a human it will have 23 chromosomes) * Follicle cells forma further protective coating – the purpose of the follicle is to produce progesterone (to maintain the uterus lining) after ovulation

Answer 14

* Flagella allows the cell to move * Lots of mitochondria to provide energy for this movement * Acrosomes (head of the sperm) contain digestive enzymes to break down the zona pellucida and allow for fertilisation * Haploid nucleus

Answer 15

* The acrosome comes into contact with the zona pellucida and the acrosome reaction occurs – enzymes digest the zona pellucida * Acrosome fuses with the cell surface membrane and allows the sperm nucleus to enter the egg cell * Cortical reaction causes the zona pellucida to harden and prevent polyspermy * Nuclei fuse together and form a diploid zygote

Answer 16

- start with a microspore mother cell. - this goes through meiosis twice to form a haploid cell - the cell with go through mitosis twice and the nuclei only divide to form a pollen tube nucleus and a generate nucleus - it develops a 2nd generate before going down the pollen tube

Answer 17

- starts with a megaspore mother cell - goes through meiosis twice to form 4 haploid cell, but 3 of them are degenerate - the cell grows - the nuclei divide by mitosis until there are 8 nuclei that are haploid - the top 3 nuclei are antipodal cells (– function is unclear, seem to provide a protective coating) - the two nuclei in the middle are polar bodies - there are two synergids at the bottom (used to help the generative nucleus reach the egg cell)

Answer 18

* Pollen grain is made up of the pollen tube nucleus and the generative nucleus * The grain sticks to the stigma where it germinates * Pollen Tube nucleus Pollen tube grows down the style by secreting digestive enzymes The enzymes break down surrounding tissue for nutrients The pollen tube grows into the embryo sac * The generative nucleus o Divides by mitosis to produce 2 sperm cells which enter the embryo sac o One of the sperm cells fuses with the female nucleus – forms the main embryo o The other fuses with the polar nuclei to produce a triploid primary endosperm nucleus – provides nutrients for the embryo

Answer 19

o Totipotent: can make any other kind of cell in the body

Answer 20

o Pluripotent stem cells are more limited – it can form any cell type except the placenta/umbilical cord

Answer 21

o Multipotent stem cells differentiate into several cell types but are limited

Answer 22

* The zygote undergoes cleavage – mitosis occurs without the interphase stage. The process occurs in the oviduct * The product of cleavage results in the blastocyst – a small collection of cells forming embryo * The outer cells of the blastocyst are totipotent and can form the placenta while the inner cells will be pluripotent and they form the rest of the foetus * The whole process takes about a week

topic 2 : cells, viruses and reproduction of living things Flashcards

(46 cards)