Meiosis/mutation

Question 1

Codon def

Answer 1

a sequence of three nucleotides which together form a unit of genetic code

Question 2

What do gene mutations involves?

Answer 2

-a change in the base sequence of chromosomes

Question 3

when can gene mutations arise?

Answer 3

-spontaneously during DNA replication

Question 4

Describe base substitution

Answer 4

-Base substitution
> a nucleotide in a DNA molecule is replaced by another nucleotide which has a different base

Question 5

what are two possible consequences of a base substitution?

Answer 5

> the a/a coded for may be changed which could affect a protein ( see protein topic )
however, new triplet of bases may still code for same a/a due to degenerate nature of genetic code, in which most a/a have more than one codon

Question 6

Describe base deletion + consequence

Answer 6

-A nucleotide is lost from the normal DNA sequence
-a/a sequence of polypeptide completely different as one deleted nucleotide causes all triplets in a sequence to be read differently as they are shifted to the left

Question 7

What can increase the rate of mutation

Answer 7

mutagenic agents

Question 8

When can mutations in the number of chromosomes arise

Answer 8

spontaneously by chromosome non-disjunction during meiosis

Question 9

How to calculate the number of different diiferent combinations of chromosomes following meiosis, without crossing over?

Answer 9

2 to the power of n, where n=number of homologous chromosome pairs

Question 10

What does meiosis produce?

Answer 10

-daughter cells that are genetically different from each other

Question 11

What is the first stage of meiosis ?

Question 12

What are three differences between meiosis and mitosis

Answer 12

-Mitosis produces cells with the same number of chromosomes as the parent cell, whereas meiosis produces cells with half the number of chromosomes as the parent cell
-Mitosis produces daughter cells that are genetically identical, meisosis produces daughter cells that are genetically different from each other and parent cell
-mitosis produces 2 daughter cells, meiosis produces four

Question 13

When would meiosis occur in an organisms life cycle?

Answer 13

-before sexual reproduction, as meiosis produces gametes which have half the number of chromosomes of the parent cell

Question 14

How does random fertilisation of haploid gametes further increase genetic variation within a species?

Answer 14

-as it creates genetic variation between zygotes (cell formed by the fusion of male and female gametes) as each will have a unique combination of alleles

Question 15

haploid def

Answer 15

A cell which has half of the usual complete set of chromosomes

Question 16

diploid def

Answer 16

A cell with a complete set of chromosomes

Question 17

What are the two stages prior to meiosis

Answer 17

-before meiosis, DNA unravels and replicates so there are two copies of each chromosome, chromatids
-The DNA condenses to form double armed chromosomes, called centromeres, each made of 2 sister chromatids, joined together by a centromere

Question 18

Describe meiosis 1 and the stage immediately after in terms of the chromosome content of cells

Answer 18

-Meiosis 1(first division), the chromosomes arrange themselves at random into homologous pairs
-these homologous pairs are then seperated, halving the chromosome number

Question 19

Describe meiosis 2, and the step immediately after in terms of the chromosome content of the cells

Answer 19

-Meiosis 2 (second division), the pairs of sister chromatids that make up each chromosome are seperated ( the centromere is divided)
-four haploid cells (gametes) that are genetically different from each other are produced

Question 20

gene

Answer 20

a length of DNA that codes for a polypeptide

Question 21

locus

Answer 21

the posistion of a gene on a chromosome or DNA molecule

Question 22

allele

Answer 22

one of the different forms of a particular gene

Question 23

homologous chromosome

Answer 23

a pair of chromosomes, one of maternal and one of paternal, that have the same gene loci

Question 24

Describe the independent segregation of of homologous chromosomes

Answer 24

-In meiosis 1 (first division) the chromosomes arrange themselves at random into homologous pairs
-one of each of these pairs will go to each daughter cell (depending on how the chromosomes are lined up)
-seeing as the pairs are lined up at random, the combination of chromosomes of maternal and paternal origin that goes into a daughter cell at meiosis 1 is also a matter of chance
-this is called independent segregation

Question 25

How does the independent segregation of homologous chromosomes result in genetic variation?

Answer 25

-each member of a homologous pair having the same genes and therefore determining the same characteristics
-but the alleles of these genes may differ
-the independent segregation of these chromosomes therefore results in new genetic combinations

Question 26

Describe the process of crossing over between homologous chromosomes and how it leads to further genetic variation among daughter cells.

Answer 26

-Meiosis 1(first division), the chromosomes arrange themselves at random into homologous pairs then:
>The chromatids of each pair become twisted around each other
> During this, tensions are created and portions of the chromatids break off
>these broken portions might rejoin with the chromatids of their homologous partner
> Usually it is the equivalent portions of homologous chromosomes that are exchanged
-in this way, genetic combinations of maternal and paternal alleles are produces
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