Genetic Variation

Question 1

What is DNA?

Answer 1

A double helix structure containing all gentic information and instructions on formation and functioning of proteins.

Question 2

What is in nucleotide?

Answer 2

Phsophate, sugar, base

Question 3

What is the phosphate bases?

Answer 3

Adenine, Cytosine, Guanine, Thymine

Question 4

What is a chromosome?

Answer 4

an (organised) structure of DNA (found in the nucleus of a cell).

Question 5

What is a gene?

Answer 5

a segment of DNA found in a small section of the chromosome that codes for a particular protein /
feature / characteristic. The base sequence provides the code for building the different proteins

Question 6

What is an alternative form of a gene?

Answer 6

an Allelle (slight differences in the base sequence cause the variations in
phenotypes which lead to genetic variation between individuals)

Question 7

What is Genetic Variation?

Answer 7

differences in phenotypes between individuals arising because of the variety of
different genotypes for traits within a population.

Question 8

What is a phenotype?

Answer 8

physical expression of genotype / alleles, eg brown or blond hair

Question 9

What is a genotype?

Answer 9

combination of alleles - for each gene there are 2 alleles, one inherited from each parent

Question 10

What is a phenotypic ratio?

Answer 10

can be expressed as ratios, fractions or percentages e.g. 3 black : 1 white, OR ¾ black
& ¼ white, OR 75% black, 25% white

Question 11

What is a genotypic ratio?

Answer 11

can be expressed as ratios, fractions or percentages e.g. 1 FF : 2 Ff : 1 ff, OR ¼ FF & ½
Ff & ¼ ff, OR 25% FF, 50% Ff and 25% ff

Question 12

How many chromosomes do humans have?

Answer 12

Humans have 46 chromosomes; 23 pairs.

Question 13

What is Mitosis?

Answer 13

cell division for growth & repair (by replacing damaged cells) – produces 2 identical daughter cells

Question 14

What is Meiosis?

Answer 14

cell division producing gametes/sex cells which have ½ the normal number of chromosomes
(haploid) as body (somatic) cells (diploid). Produces 4 genetically different daughter cells.

Question 15

What is the crossing over process?

Answer 15

Meiosis shuffles existing alleles because of crossing over of homologous chromosomes and independent
assortment of chromosomes. Crossing over happens during the first stage of meiosis when the
homologous pairs of chromosomes line up in the middle of the cell and a small pieces of DNA are swapped
between them. This results in a mixing of alleles between daughter cells.

Question 16

Gamete fact!

Answer 16

A gamete (egg or sperm) has half the normal number of chromosomes as body cells to ensure that when
a sperm fuses with an egg the resulting zygote has the correct number of chromosomes

Question 17

What is fertilization?

Answer 17

is random which male gamete fertilises the female gamete - resulting in new combinations
of alleles - producing a unique zygote.

Question 18

What is sexual reproduction?

Answer 18

produces variation between individuals due to random assortment of chromosomes
in meiosis and random fertilisation.

Question 19

Advantages of variation for species

Answer 19

some individuals may survive if some change to environment /
threatening event occurs, e.g. drought, disease (selection pressures). If a new disease arrives, not all
individuals will be wiped out. Individuals best suited to an environment will survive to reproduce and pass
on their genes to future generations.

Question 20

What is a mutation?

Answer 20

a change to the base sequence of a gene / change in the genetic code & therefore a new
protein / characteristic / trait being made. Mutations result in new alleles being created within a population.
(Crossing over & independent assortment in meiosis cause a mixing of existing alleles)

Question 21

When can mutations be passed on?

Answer 21

A mutation occurring in a gamete won’t affect the individual but can be passed on / inherited. The
offspring have this mutation in every cell and it can be passed on in their gametes. Mutations in a somatic
(body) cells e.g. a skin cell, cannot be inherited.

Question 22

A-Sexual vs. Sexual reproduction

Answer 22

Sexual repro. uses meiosis - offspring genetically different - takes longer
time – needs 2 parents – but offspring have better disease survivability. Asexual repro - uses mitosis -
all offspring are the same - produces identical offspring, in large numbers, much more quickly – but
offspring have lack of disease survivability