Meiosis And Genetic Variation

Question 1

What is mitosis?

Answer 1

-produces two daughter cells with the same number of chromosomes as the parent cell and as each other

Question 2

What is meiosis?

Answer 2

-usually produces four daughter cells each with half f the number of chromosomes as the parent cell

Question 3

why is meiosis important?

Answer 3

• in sexual reproduction two sets of gametes fuse to give rise to new offspring
• if each gamete had a full set of chromosomes then the cell that they produce has double this number
• this would mean that the number of chromosomes in a cell would double with each generation
• meiosis maintains a constant number of chromosomes in adults by halving the number of chromosomes during the life cycle

Question 4

what is the haploid number?

Answer 4

-single set of chromosomes

Question 5

what is meiosis 1?

Answer 5

• in the first division homologous chromosomes pair up and chromatids wrap around each other
• equivalent portions of these chromatids may be exchanged through crossing over
• by the end of meiosis one the homologous pairs have separated with one chromosome from each pair going into one of the two daughter cells

Question 6

what is meiosis 2?

Answer 6

• in the second meiotic division the chromatids move apart

- at the end of meiosis two four cells have been formed

Question 7

how does meiosis cause genetic variation?

Answer 7

• through independent segregation of homologous chromosomes

- new combinations of maternal and paternal alleles through crossing over

Question 8

what does meiosis produce?

Answer 8

-genetic variation among offspring which leads to adaptions that improve survival chances

Question 9

what is the definition of a gene?

Answer 9

-a length of DNA that codes for a polypeptide

Question 10

what is the definition of locus?

Answer 10

-the position of a gene on a chromosome or DNA molecule

Question 11

what is an allele?

Answer 11

-one of the different forms of a particular gene

Question 12

what is a homologous chromosome?

Answer 12

-a pair of chromosomes (one maternal and one paternal) that have the same loci

Question 13

what is the independent segregation of homologous chromosomes?

Answer 13

• during meiosis one each chromosome lines up alongside its homologous partner
• when these pairs arrange themselves in this line they do so at random
• one of each pair is passed will pass to each daughter cell depends on how the chromosomes are lined up in the parent cell
• the combination of maternal and paternal chromosomes in the daughter is down to change which is called independent segregation

Question 14

how does variety come from new genetic combinations?

Answer 14

• each member of a homologous pair of chromosomes has exactly the same genes and so determined the same characteristics however some of the alleles of these groups may differ
• the independent assortment of these chromosomes produces new genetic combinations

Question 15

what happens when homologous chromosomes split?

Answer 15

• one of the pair of chromosomes contains specific genes and the other pair contains a different specific gene so there are two possible arrangements which are equally probable
• at the end of meiosis 1 the homologous chromosomes have segregated into two separate cells
• at the end of meiosis 2 the chromosomes have segregated into chromatids producing four gametes for each arrangement
• the actual gametes are different depending on the original attachment if chromosomes at stage 1

Question 16

What is crossing over?

Answer 16

-the chromatids cross over one another many times

Question 17

What is the process of recombination?

Answer 17

-the broken off portions of chromatids recombine with another chromatid

Question 18

What happens when homologous chromosomes line up along the equator?

Answer 18

• the chromatids of each pair becomes twisted around one another
• during this twisting process tensions are created and portions of the chromatids break off
• these broken portions might then rejoin with the chromatids of its homologous partner
• usually it’s the equivalent portions of homologous chromosomes that are exchanged so new genetic combinations of maternal and paternal alleles are produced

Question 19

What happens when a cell produced by meiosis is a gamete?

Answer 19

• they will be genetically different as a result of the different combinations of the maternal and paternal chromosomes they contain
• haploid gametes fuse randomly so produces variety in offspring
• when gametes come from different parents two different genetic make ups are combined and even more variety in results