meiosis

Question 1

what are the 2 types of mutation

Answer 1

gene mutation
chromosme mutation

Question 2

what are gene mutations

Answer 2

change in the sequence of bases on the DNA

ultimately changes AA code and protein

Question 3

what are chromosome mutations

Answer 3

a change in the no of chromosomes or change in the overall structure of a chromosome

Question 4

what are spontaneous gene mutations

Answer 4

random mistakes occurring in DNA replication
no particular cause and occur with low frequency

Question 5

how can the rate of mutation be increased

Answer 5

by exposure to mutagenic agents

radiations- x-rays and UV light
some chemicals eg benzpyrene in tobacco smoke which damages base cystosine
infectious agents eg HPV

Question 6

what are the 4 types of gene mutation

Answer 6

-addition
-deletion
-substitution
-inversion

Question 7

what is an addition mutation

Answer 7

one or more bases are added
thus frameshift and shifts reading frame-diff protein

Question 8

what is a deletion mutation

Answer 8

one or more bases are deleted from sequence
thus frameshift and shift in reading frame - diff protein

Question 9

what are substituition mutations

Answer 9

one nucleotide base or codon is exchanged for another so only triplet is affected
non-frameshift as only affect on triplet coden so not reading frame

Question 10

what are inversion mutations

Answer 10

a base pr a sequence of bases is reversed
non-frameshift

Question 11

what are the consequences of gene mutations

Answer 11

silent mutations - no effect
due to the removal of introns / mini satellite
code is degenerate - one codon for multiple

mis-sense- leads to formation of altered proteins
sequence of bases changed = altered mRNA
altered mRNA can be translated to diff AA seq
may then form protein w altered tertiary struct
causes affect on function

can be beneficial - advantageous characteristics
or harmful as non-functional

Question 12

nonsense

Answer 12

codon changed to STOP codon then translation is ended prematurely and will be non-functional
has a serious affect on cell

Question 13

what are the chromosome mutations

Answer 13

deletion- segment of chromosome is lost - vital genes could be lost
translocation- segment transferred onto another
duplication- section of chromo is transferred onto its homologous counterpart- so now had 2
inversion- large segment of chromo is now reversed

Question 14

how are the changes in chromo number referred as

Answer 14

small-scale losses or small-scale gains

Question 15

what is gaining a chromo called

Answer 15

trisomy eg downs syndrome

Question 16

what is losing a chromo called

Answer 16

monosomy

Question 17

what is having a complete extra set of chrome called

Answer 17

polyploidy - only plants

Question 18

how many divisions are in meiosis

Answer 18

2

Question 19

what are haploid cells

Answer 19

half the diploid number with 1 chromosome from each pair - represented a n

Question 20

what are diploid cells

Answer 20

full set of chromosomes in pairs- represented as 2n

Question 21

what are the phases of meiosis

Answer 21

meiosis 1
pro 1
meta 1
ana 1
tela 1

meiosis 2
pro 2
meta 2
ana 2 tela 2

Question 22

what occurs in prophase 1

Answer 22

-DNA condenses and becomes visible as chromosomes
-DNA replication has already occurred so each chromosome consists of two sister chromatids joined together by a centromere
-The chromosomes are arranged side by side in homologous pairs
-A pair of homologous chromosomes is called a bivalent - formed in a process known as synapsis
-As the homologous chromosomes are very close together the crossing over of non-sister chromatids may occur. The point at which the crossing over occurs is called the chiasma (chiasmata; plural)
-In this stage centrioles migrate to opposite poles and the spindle is formed
-The nuclear envelope breaks down and the nucleolus disintegrates
-spindle forms

Question 23

what occurs in metaphase 1

Answer 23

-bivalents become arranged on the equator of the spindle

Question 24

what occurs in anaphase 1

Answer 24

-one chromosome from each bivalent is pulled toward opposite poles of the spindle
-the centromeres do not divide
-it is important to remember that each bivalent acts independently so each pole receives a mix of mat and pat chromosomes

Question 25

what occurs in telophase 1

Answer 25

- each pole of cell- now a haploid set of chromo, one from each homologous pair -chromosomes decondense - nucleoli and nuclear membrane reappear

Question 26

what is the role of meiosis 1

Answer 26

to produce two haploid cells - in humans -23

Question 27

how does meiosis 1 introduce variation

Answer 27

cross-over events independent/ random assortment

Question 28

what occurs in prophase 2

Answer 28

- chromo condense - nucleoli disappear -nuclear mem breaks down -centrioles migrate towards opposite poles of cell - spindle forms

Question 29

what occurs in metaphase 2

Answer 29

- chromosomes line up on the equator of the spindle

Question 30

what occurs in anaphase 2

Answer 30

-centromeres split and chromatids are pulled to opposite poles of the cell

Question 31

what occurs in telophase 2

Answer 31

-chromatids decondense -nuclear mem reform -nucleolus reappear -spindle breaks down -centrioles disappear

Question 32

what then occurs after telophase 2

Answer 32

cytokinesis then takes place and produces 4 haploid daughter cells

Question 33

what is the significance of meiosis

Answer 33

halves no. of chromosomes producing haploid cells introduces variation

Question 34

what is the role of meiosis

Answer 34

to produce non-genetically identical daughter cells which are known as gametes

Question 35

what is a cross-over event

Answer 35

Crossing over is the process by which non-sister chromatids exchange alleles Process: -During meiosis I homologous chromosomes (form bivalent) pair up and are in very close proximity to each other -The non-sister chromatids can cross over and get entangled -These crossing points are called chiasmata -As a result of this a section of chromatid from one chromosome may break and rejoin with the chromatid from the other chromosome this generates large amounts of variation

Question 36

what is independent assortment

Answer 36

Independent assortment is the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase I

Question 37

how does independent assortment occur

Answer 37

homologous chromo pair up and then separate to opposite poles of the cell - each pair acts independently so random mix

Question 38

what does the possible no. of chromo combo equal to

Answer 38

The number of possible chromosomal combinations resulting from meiosis is equal to 2^n n is the number of homologous chromosome pairs

Question 39

what are some differences bwt mitosis and meiosis

Answer 39

The Different Outcomes of Mitosis and Meiosis Number of daughter cells Mitosis = 2 Meiosis = 4 Ploidy of daughter cells Mitosis = 2n Meiosis = n Are the daughter cells genetically identical to the parent cells and each other? Mitosis = yes Meiosis = no - cross over / IA meiosis - 2 divisions mitosis - 1 division meiosis - production of gametes mitosis - asexual rep and tissue growth + repair

Question 40

how does IA affect fertilisation

Answer 40

During fertilisation any male gamete can fuse with any female gamete to form a zygote This random fusion of gametes at fertilization creates genetic variation between zygotes as each will have a unique combination of alleles There is an almost zero chance of individual organisms resulting from successive sexual reproduction being genetically identical

Question 41

what is non-disjunction

Answer 41

the failure of either chromosomes or chromatids to separate and leads to gamete with abnormal chromo numbers this can happen in either meiosis 1 or 2 results in chromosome mutation

Question 42

how do you determine where meiosis occurs in a life cycle

Answer 42

when chromosome number halves 2n - n NOT WHEN ALWAYS WHEN PRODUCE GAMETES work out the adult cell in each - will be 2n

Question 43

the formula to calculate the number of combinations of chromosomes after the random fertilisation of two gamete

Answer 43

(2n)^2

Question 44

suggest why flower buds are often used to show meiosis

Answer 44

site of meiosis/ plants reproductive organs

Question 45

why is it important that one chromo from each pair ends up in each new cell

Answer 45

-so that all of the cells produced are haploid -so when fetilisation takes place the cell produced is diploid

Question 46

what is the difference in homologous chromosomes

Answer 46

contain different alleles/ versions of the same gene