N5 -U2 (MO) - KA4 Variation & inheritance Flashcards
Describe the term variation
Although members of a species are similar to one another, they are not identical. This is because variation exists among the members of a species.
What are the 2 types of variation?
Discrete and Continuous variation
Describe with examples the term discrete variation
This variation comes from single gene inheritance.
Here members of a species can be divided into 2 or more distinct groups.
e.g. Blood types (4 groups, a, b, ab and o)
** Tongue rolling (2 groups can roll or cannot roll)
Describe with examples the term continuous variation
This variation comes from polygenic inheritance (more than 1 gene). Here members of a species vary in a smooth continuous way (where there is a range of values between a minimum and maximum).
e. g. Height
* * muscle shell length
How would the data for discrete variation be presented?
It is normally presented in a bar graph, with each separate distinct group represented as a bar
How would the data for continuous variation be presented?
A histogram is initially produced. After this a curve is drawn from/over the histogram, this gives a bell-shape curve also known as a normal distribution curve.
Where is the genetic information found that is responsible for variation?
In the nucleus, the information is contained in genes on chromosomes.
Why is sexual reproduction significant to variation?
During sexual reproduction half of the genetic material is received from one parent and half from the other parent. The offspring will resemble each parent in some ways and differs from each parent in other ways
Define Phenotype
The particular version of a characteristic seen in an individual is described as their phenotype and is determined by the genes on the chromosomes they inherited from their parents.
Define Allele
Different forms of the same gene.
Define genotype
The alleles that an organism has for a particular characteristic, usually written as letters.
What does dominant mean?
An allele that always expresses itself whether it is partnered by a recessive allele or by another like itself.
What does recessive mean?
Describes the variant of a gene for a particular characteristic which is masked or suppressed in the presence of the dominant variant. A recessive gene will remain dormant unless it is paired with another recessive gene (e.g. mm).
What does homozygous mean?
This describes a genotype in which the two alleles for the characteristic are identical. (e.g. mm or MM)
What does heterozygous mean?
This describes a genotype in which the two alleles for a particular characteristic are different. (e.g. Mm)
What is a monohybrid cross?
A genetics cross that shows the inheritance of one characteristic.
When looking at monohybrid crosses, what do the letters, P, F1 and F2 represent?
P = Parent generation F1 = Refers to first generation offspring in genetic inheritance. F2 = Refers to the second generation offspring in genetic inheritance.
Define the term true-breeding
A true breeding is a kind of breeding wherein the parents would produce offspring that would carry the same phenotype (identical to parents). This means that the parents are homozygous for every trait. … With plants, true breeding occurs when plants produce only offspring of the same variety when they self-pollinate.
What can always be said about the phenotypes of the members of an F1 generation resulting from a cross of true breeding parents.
They are all identical to one another!
R = Dominant for round seed
r = Recessive for wrinkled seed.
What ratio of F1 would be wrinkled if both parents were heterozygous dominant?
3:1
3 round to 1 wrinkled
R = Dominant for round seed
r = Recessive for wrinkled seed.
What ratio of F1 would be wrinkled if one parent was heterozygous dominant and the other recessive?
2:2
1:1 (always simplify the ratio!)
so 50% f1 wrinkles and 50% round
What are the reasons why predicted phenotype rations among offspring are not always achieved?
However, predicted phenotype ratios among offspring are not always achieved. This can be for a variety of reasons, for example the sample size being too small or the ratios based on fertilisation (which is a random process). (imagine throwing a dice and the first 5 throws gives you a 6, not what you would expect eh??? it involves the element of chance)
What is a pedigree chart?
A family tree diagram which show the inheritance of a genetic condition in a family, eg cystic fibrosis
Define polygenic inheritance!
The type of inheritance determined by the interaction of several genes (usually 3 or more genes) acting together eg skin colour.
As well as the genotype what also influences polygenic inheritance?
Many phenotypes are also affected by environmental factors, such as the conditions to which the individual has been exposed. For example, a person’s height is determined by the genes they have inherited and by the availability of food when they are growing.
