Lecture 28: Meiosis And Genetic Diversity

Question 1

Compare the outcomes of mitosis and meiosis
Chromosome behaviour
Chromosome number
Genetic identity of daughter cells

Answer 1

Chromosome behaviour:
Mitosis: independant 
Meiosis: homologous pairs zipper together 
Chromosome number:
Mitosis: diploid 46
Meiosis: haploid 23
Genetic identity of daughter cells: 
Mitosis: identical 
Meiosis: new assortment from parents

Question 2

Meiosis differs in two fundamental aspects from mitosis:

How?

Answer 2

1. First it uses an exchange of information between sister chromatids to generate new combinations of genetic info (combines info from both of the organisms parents)
2. Second, it splits chromosomes into chromatids during the second phase to generate haploid cells with only half the genetic information of their parent, diploid cells.

Question 3

What are the stages of meiosis?

Answer 3

Meiosis involves two divisions that can be divided into meiosis 1 and meiosis 2
Meiosis 1:
Crossover at prophase 1:
Homologous chromosomes cross over, exchanging segments. By the end of telophase 1 the members of homologous pairs have separated from each other.
-it is during prophase 1 that an important event occurs–> non sister chromatids zipped together and then crossover to form new combinations. The outcome is that new parents chromosomes are produced in the gametes

The first division of meiosis provides 2 ways of combining genetic info:

1) cutting apart and pasting together various segments of homologous chromosomes to yield unique hybrid chromosomes
2) independent assortment of maternal and paternal chromosomes to the poles of each cell

Meiosis 2:
During this the two parental copies of each chromosomes are randomly sorted into daughter cells as the sister chromatids separate during anaphase 2.
The second division of meiosis separates the chromatids. Once again, the spindle fibres provide pulling power. Once chromatids are separated, they are called chromosomes, and so at the end if meiosis 2, each of the 4 new cells has the haploid number of chromosomes

Question 4

Genetic diversity
How is genetic diversity maintained
How does sexual reproduction contribute to genetic diversity
The offspring must have the same number of chromosomes as each parent, how is that possible?

Answer 4

Sexual reproduction allows for diversity, because when 2 individuals reproduce they bring forth a new individual with a unique mixture of characteristics. Diversity allows for populations to better survive and adapt to changing conditions.
In asexual reproduction, the whole population is basically identical so are less likely to adapt to changing environment.
The offspring must have the same number of chromosomes as each parent, how?
Meiosis produces haploid cells (1n) which contain just one member of every chromosome pair characteristic of an organism

Question 5

What are the outcomes of sexual reproduction?

Answer 5

At fertilisation haploid egg and sperm cells combine to produce a zygote that is then diploid. The zygote has a full set of chromosomes with half coming from each parent.

Question 6

What is the function if meiosis

Answer 6

• to produce eggs and sperm for sexual reproduction
• to reduce the chromosome number by half when gametes are formed
• to allow for genetic diversity by permitting swapping of each parents gene when gametes are produced.

Question 7

Overview of meiosis

Answer 7

There are two consecutive cell divisions- meiosis 1 and meiosis 2
Meiosis results is four cells with only one set of chromosomes (haploid cells)