R9 mitosis and meiosis

Question 1

What is ploidy ?

Answer 1

The number of chromosomes in a cell

Question 2

In terms of n, what is the karyotype ?

Answer 2

2n

Question 3

What is the centromere and telomere in respects to cell division ?

Answer 3

Centromeres – heterochromatin, binds to the kinetochore during mitosis

Telomeres – heterochromatin, repetitive DNA, protects from degradation

Question 4

What are sister kinetochores ?

Answer 4

Each sister chromatid have their own, they bind to the spindle fibre during mitosis

Question 5

What is cohesin and its role in mitosis ?

Answer 5

Cohesin protein complexes hold together sister chromatid. These are then progressively removed during mitosis freeing the arms of the chromosome. The centromeric cohesin are degraded during mitosis to separate the sister chromatid.

Question 6

How do bacteria reproduce?

Answer 6

Binary fission, asexual reproduction

Question 7

How do mitochondria and chloroplast replicate ?

Answer 7

during mitosis they use binary fission, then are partitioned and distributed in the daughter cells, this is a form of inheritance (5th mode)

Question 8

What is separated in meiosis 1 and 2?

Answer 8

• Meiosis I – homologous chromosomes separated first
• Meiosis II – sister chromatid separated.

Question 9

What does programmed DSB achieve at the beginning of meiosis ?

Answer 9

This causes homologous chromosomes to pair up in a synaptonemal complex, this is assembled and disassembled in prophase 1, this ultimately forms a bivalent.

Question 10

What is crossing over and a chiasma ?

Answer 10

Crossover – reciprocal exchange of chromosomal segments due to the DSB repair.
Chiasma – site of the crossover

Segregation of homologous chromosomes require at least 1 crossover. Chiasmata holds together until the SC has disassembled.

Question 11

Why is crossing over important ?

Answer 11

causes new combinations of alleles. These are beneficial or not based on the environment.

• Prevents accumulation of deleterious mutations
• Recombination of X and Y is impossible, except for in the pseudo-autosomal regions located at the very ends of the arms.

Question 12

How can we prove trans-generational inheritance of epigenetic marks in animals and plants ?

Answer 12

F2 in plants (dont set aside their germline)

F3 in animals

Question 13

What is Spermatogenesis and oogenesis ?

Answer 13

are types of gametogenesis and they are the products of meiosis.

• Spermatogenesis occurs constantly whereas oogenesis occurs once a month, sperm germline can mitotically divide throughout a lifetime
• Haploid gametes will produce diploid individuals via fertilisation

Question 14

What is DNM ?

Answer 14

Present for the first time in a family.

De novo mutation (DNM) occurring during gamete production can be inherited by offspring.

• Older dads contribute more mutations due to the number of cell divisions in the germline
• Maternal age influences risk of chromosomal miss-segregation.

Question 15

What is parasexuality ?

Answer 15

acquisition of DNA (that can recombine with chromosomes or be retained as plasmids)

• Transduction – transfer via viruses infecting bacteria
• Conjugation – transfer via physical contact
• Transformation – uptake from surrounding environment

Question 16

What is gene dosage ?

Answer 16

copy number of the genes that influences the number of corresponding RNA and proteins. In us its 2.

• Deviations (unbalanced chromosome segregation) can result in pathological conditions but also act as a driver for evolution

Question 17

What is the problem with too much or too little protein ?

Answer 17

Too little will no promote a reaction, too much will cause accumulation especially if they are involved in complexes

Question 18

What will be the expression level on the X chromosome in XX vs XY

Answer 18

They will have the same level of expression

Question 19

How is the same level of expression achieved in XY and XX

Answer 19

• One of the two X chromosomes (XX) is completely inactivated
• DNA methylation and repressive histone methylation = extreme packing, no expression of one of the X chromosomes. This is completely random and down to chance

Question 20

What are some methods to maintain a good gene dosage ?

Answer 20

dampening expression from both the “over-represented” chromosomes (repressive histone methylation) or ramping up expression of the “under-expressed chromosome (histone acetylation)
- Autosomes don’t have compensation mechanisms leading to higher risk of health issues.

Question 21

What happens to gene dosage in cancer cells ?

Answer 21

extensive changes in dosage due to the mutation rate being very high

Question 22

Can plants tolerate aneuploidy ?

Answer 22

Yes, seed pods can be trisomic, dosage compensation is present in some autosome

Question 23

Why does not recombination occur in mt-DNA ?

Answer 23

‘one-sided’ nature of inheritance

• Sets of alleles are inherited in blocks (haplotypes), new haplotypes arise only via mutation which produce new alleles.
• We cannot track back to the first male and female as they may not have been alive at the same time, won’t go back to the first human
• They were the best at spreading their genes.