Genetic Variation Flashcards
What is DNA?
A double helix structure containing all gentic information and instructions on formation and functioning of proteins.
What is in nucleotide?
Phsophate, sugar, base
What is the phosphate bases?
Adenine, Cytosine, Guanine, Thymine
What is a chromosome?
an (organised) structure of DNA (found in the nucleus of a cell).
What is a gene?
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
What is an alternative form of a gene?
an Allelle (slight differences in the base sequence cause the variations in
phenotypes which lead to genetic variation between individuals)
What is Genetic Variation?
differences in phenotypes between individuals arising because of the variety of
different genotypes for traits within a population.
What is a phenotype?
physical expression of genotype / alleles, eg brown or blond hair
What is a genotype?
combination of alleles - for each gene there are 2 alleles, one inherited from each parent
What is a phenotypic ratio?
can be expressed as ratios, fractions or percentages e.g. 3 black : 1 white, OR ¾ black
& ¼ white, OR 75% black, 25% white
What is a genotypic ratio?
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
How many chromosomes do humans have?
Humans have 46 chromosomes; 23 pairs.
What is Mitosis?
cell division for growth & repair (by replacing damaged cells) – produces 2 identical daughter cells
What is Meiosis?
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.
What is the crossing over process?
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.
Gamete fact!
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
What is fertilization?
is random which male gamete fertilises the female gamete - resulting in new combinations
of alleles - producing a unique zygote.
What is sexual reproduction?
produces variation between individuals due to random assortment of chromosomes
in meiosis and random fertilisation.
Advantages of variation for species
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.
What is a mutation?
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)
When can mutations be passed on?
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.
A-Sexual vs. Sexual reproduction
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
