Variation

Question 1

Variation

Answer 1

Variation occurs in meiosis and refers to different ways genetic differences are created between individuals

Question 2

3 Processes of variation

Answer 2

1. Crossing over
2. Random assortment
3. Non - disjunction

Question 3

Crossing over

Answer 3

1. The process of crossing over occurs in the prophase of the first meiotic division
2. When chromosomes are aligned with their homologous partner they can exchange genetic material - a process called recombination
3. The points where they cross are called the chiastma.
4. As each chromosome will likely contain different alleles for the genes that they carry, crossing over will result in a different combination of alleles (in the gametes that are different from the parent cell) on the affected chromosomes.

Question 4

recombinations

Answer 4

Crossing over can result in a new combination of alleles along the chromosomes.

Question 5

Random assortment

Answer 5

Each chromosome of a homologous pair will have come from either your mother or father (maternal or paternal).

However, when they line up in metaphase 1, where they come from doesn’t influence which centriole they will move towards.

With 23 homologous pairs of chromosomes, there are 2^23 potential chromosome combinations that a gamete could inherit

Question 6

Non-disjunction

Answer 6

1 or more pairs of chromosomes fail to separate during anaphase 1 and anaphase 2 in meiosis.

1 daughter cell will receive an extra chromosome an the other will lose 1

therefore one will have 22 and the other will have 24 instead of 23

when the gamete with the extra or missing chromosome combines with another gamete during fertilisation, this can lead to trisomy 21 (down - syndrome), where there are 3 chromosomes when they should be a pair, or monosome (tuner syndrome)

Question 7

Trisomy 21 (down-syndrome)

Answer 7

Trisomy is a condition in which an individual inherits an extra copy of a chromosome, 3 copies instead of the normal two.

In this disorder, the extra coy of chromosome 21 results in a characteristic facial appearance, variable degrees of intellectual disability and physical abnormalities.

Question 8

Monosomy (turner syndrome)

Answer 8

Where an individual is missing a chromosome, they have only one copy instead of the normal two.

Monosomy usually results in sever malformations and often miscarriage