Meiosis

Question 1

meiosis

Answer 1

produces daughter cells that are genetically different from each other.

Question 2

Describe the process of Meiosis

Answer 2

Before meiosis starts, DNA replicates so there are two copies of each chromosome, called sister chromatids, joined by a centromere
Meiosis I separates homologous pairs
Chromosomes arrange into homologous pairs
Crossing over (prophase I) creates genetic variation in gametes
Independent segregation (metaphase I) increases genetic variation in gametes
Meiosis II separates chromatids
Creates 4 haploid cells (from a single diploid parent cell) that are genetically varied.

Question 3

state how meiosis creates genetic variation

Answer 3

crossing over
Independent segregation/random assortment
Random fertilisation

Question 4

explain how meiosis creates genetic variation- crossing over

Answer 4

Crossing over between homologous chromosomes
Sections of chromatids exchanged;
sections have different alleles;
creates new combinations of alleles;

Question 5

explain how meiosis creates genetic variation-independent segregation

Answer 5

Random alignment of homologous pairs at equator → random which chromosome from each pair goes to each daughter cell
Creates different combinations of maternal and paternal chromosomes and alleles in
daughter cells

Question 6

explain how meiosis creates genetic variation- random fertilisation

Answer 6

Random fertilisation when two gametes fuse to form a zygote

Question 7

What are the advantages of variation

Answer 7

some better adapted;
Some survive
To reproduce;
Pass on gene/allele;
Allows for changing environment/different
environment

Question 8

Describe what happens to chromosomes in meiosis.

(6 marker)

Answer 8

1. Chromosomes condense;
2. Chromosomes associate in homologous pairs (bivalents)
3. Crossing-over (chiasma formation)
4. Join to spindle fibres
5. Join via centromere
6. At equator/middle of cell
7. Independent assortment”
8. Homologous chromosomes move to opposite poles
9. Pairs of chromatids separated in 2nd division;

Question 9

Explain the importance of meiosis

Answer 9

Two divisions – creates haploid gametes
Diploid number restored at fertilisation
Maintains chromosome number from one generation to the next
Independent segregation and crossing over creates genetic variation

Question 10

What is the formula to calculate the number of possible different combinations of
chromosomes in daughter cells following meiosis?

Answer 10

2^n

(where n = the number of pairs of homologous chromosomes)

Question 11

What is the formula for the number of different combinations of chromosomes
following the random fertilisation of two gametes

Answer 11

(2n)^2 (that’s squared btw)

(where n = the number of pairs of homologous chromosomes)

Question 12

example question for meiosis calculation

Calculate the number of possible chromosome combinations produced from the
fertilisation of two gametes from separate individuals whose diploid number is 12

Answer 12

Number of homologous chromosomes = 12/2 = 6

= (26)2 = 4096

Question 13

Explain the different outcomes of mitosis and meiosis

Answer 13

-Mitosis produces diploid cells whereas meiosis produces haploid cells
-Two divisions in meiosis whereby homologous chromosomes separate then chromatids separate, whereas one division in mitosis whereby only sister chromatids separate
-Daughter cells genetically identical to each other and parent cell in mitosis whereas in meiosis, daughter cells are genetically varied
-Crossing over and independent segregation during
meiosis I whereas no crossing over in mitosis
-Mitosis produces 2 daughter cells whereas meiosis produces 4 daughter cells