meiosis + chromosomal mutations

Question 1

What are homologous pairs of chromosomes? Where do the members of the pair come from?

Answer 1

Homologous pairs of chromosomes are matching pairs of chromosomes that can possess different versions of the same genes / alleles. One member of the pair comes from the male parent and the other from the female parent.

Question 2

Diploid is…

Answer 2

Diploid is an eukaryotic cell or organism containing 2 complete sets of chromosome (2 copies of each homologous chromosome), shown as 2n

Question 3

Haploid is…

Answer 3

Haploid is an eukaryotic cell or organism containing only one complete set of chromosomes (only one of each homologous pair of chromosomes), shown as n (e.g. human sperm / egg)

Question 4

Why is meiosis called the reductive division? How does this play a part in sexual reproduction?

Answer 4

It is a different type of nuclear division that results in daughter nuclei each containing HALF the number of chromosomes of the parent cell.
In sexual reproduction, two haploid sex cells (gametes) fuse during fertilisation, to form a diploid zygote: Meiosis produces haploid gametes, which keeps the chromosome number from doubling each time sexual reproduction occurs. When the haploid gametes fuse, the resulting cell has the diploid condition again.

Question 5

Meiosis is a continuous process between the 4 phases: ______, ______, ______ and ______. It involves __ divisions of the nucleus (name them!)

Answer 5

Meiosis is a continuous process between the 4 phases: prophase, metaphase, anaphase and telophase. It involves 2 divisions of the nucleus: Meiosis I and Meiosis II.

Question 6

What is the pairing of homologous chromosomes called?

Answer 6

Synapsis

Question 7

______ _____ between non-sister chromatids results in new combinations of genes on the chromosomes.

Answer 7

Crossing over between non-sister chromatids results in new combinations of genes on the chromosomes.

Question 8

What is the point of the joint between different chromatids called?

Answer 8

Chiasma

Question 9

What is the difference between anaphase in mitosis and anaphase I in meiosis I?

Answer 9

Separation of homologous pairs of chromosomes in anaphase I and separation of sister chromatids in anaphase.

Question 10

After telophase I, the 2 cells do not go into _____ but continue into ______ __ directly.

Answer 10

After telophase I, the 2 cells do not go into interphase but continue into Meiosis II directly.

Question 11

______ __ is remarkably similar to mitosis.

Answer 11

Meiosis II is remarkably similar to mitosis.

Question 12

When drawing meiosis II, draw the centrosomes ___ degrees from original

Answer 12

When drawing meiosis II, draw the centrosomes 90 degrees from original

Question 13

In telophase II, nuclear envelopes are formed around how many groups of chromatids? How many daughter cells are produced

Answer 13

Nuclear envelopes form around the 4 groups of chromatids so 4 nuclei are formed. There are 4 daughter cells produced

Question 14

Why do the 4 haploid cells produced by meiosis differ genetically from one another?

Answer 14

1. Independent assortment of maternal and paternal homologous chromosomes (the way the chromosomes of each homologous pair line up at the equator of the spindle in meiosis I is random)
2. The crossing over of segments of individual maternal and paternal homologous chromosomes (results in new combinations of genes on the chromosomes of haploid cells produced + generates an unimaginable degree of variation / unlimited recombination)
3. Random fusion of male and female gametes in sexual reproduction

Question 15

What are mutations?

Answer 15

Mutations are changes to the genome of the cell. This may involve changes to the DNA sequence of genes. Chromosomal mutations can also arise due to a change in chromosomal number + structural modifications of chromosomes.

Question 16

What are some genetic diseases?

Answer 16

Down syndrome, Patau syndrome, Edward’s syndrome, Turner syndrome, Klinefelter syndrome, Cri-du-chat syndrome

Question 17

What is trisomy?

Answer 17

Trisomy is a condition arising when the cells of an organism has three copies of a chromosome instead of the usual two (2 due to having a pair of homologous chromosomes). It causes genetic diseases like down syndrome (Trisomy-21) and Edward’s syndrome (Trisomy-18)

Question 18

________ can occur during meiosis I or II hence producing gametes with an incorrect number of chromosomes. Define _______?

Answer 18

Non-disjunction can occur during meiosis I or II hence producing gametes with an incorrect number of chromosomes. It is the failure of 2 homologous chromosomes of a pair to separate to the opposite poles at anaphase I OR failure of sister chromatids to separate at anaphase II

Question 19

What happens when a normal gamete fertilises a gamete with an extra chromosome?

Answer 19

The result is a zygote with a total of 2n + 1 chromosomes (aneuploidy: a condition in which an organism has one or a few chromosomes above/below the normal chromosome number)

Question 20

Elaborate on the structural modifications of chromosomes, deletion and duplication

Answer 20

Deletion: results from the breakage of a chromosome in which genetic material is lost during cell division
Duplication: new genetic material is generated, resulting in extra genetic material

Question 21

Elaborate on the structural modifications of chromosomes, inversion and translocation

Answer 21

Inversion: rearrangement of the genes where the broken segment is reversed and inserted back into the same chromosome
Translocation: caused due to the rearrangement of parts between non-homologous chromosomes, the piece of chromosome detaches from 1 of the chromosome and moves to a new position to another chromosome.