6.1.2 - Patterns of inheritance Flashcards
Define genotype
This is the genetic make up of an organism in respect to that gene
Define phenotype
Observable characteristics of an organism
What is a dominant allele ?
The version of the gene that will always be expressed if present in an organism
What does showing the dominant characteristic mean ?
They could have one or two copies of the dominant gene
What is a recessive allele ?
Will only be expressed if two copies of the allele are present in this organism
What does showing the recessive characteristic mean ?
They must have two alleles coding for the recessive phenotype
What is variation?
- Differences in characteristics within species
- Can be interspecific or intraspecific
Define intraspecific variation
Differences between individuals within the same species
Define interspecific variation
Differences between individuals that are from a different species
What are the 2 causes of variation?
Environmental and genetic
Are environmental effects heritable?
No
Give 2 examples of environmental effects
- Hair dye
- Diet
Are genetic factors heritable?
Yes
Give 4 causes of genetic variation
- Presence of a different allele
- Random fertilisation of gametes
- Meiosis
- Independent assortment and crossing over specifically
- Mutations
What are the two sources of variation in meiosis?
- Crossing over
- Independent assortment
What are the two types of variation?
Continuous and discontinuous
What is continuous variation?
- Variation from one possible extreme to another, can be anywhere between both ends of the spectrum
- It can be plotted to give a normal distribution curve
Give 2 examples of continuous variation
- Height
- Weight
What is discontinuous variation?
- Discrete groupings of individuals
- Presented as a bar chart
Give an example of discontinuous variation
Blood group
Why does continuous variation occur?
Due to the inheritance of 2 or more genes
Why does discontinuous variation occur?
Result of inheritance of one gene with 2 or more alleles
Is continuous variation influenced by the environment?
It can be
Is discontinuous variation influenced by the environment?
No
What is a polygenic characteristic ?
A characteristic that is controlled by two or more genes
What is a multifactorial characteristic ?
A characteristic that involves both genetic and environmental factors
Define monogenic inheritance
When the inheritance of a single gene is shown
When does codominance occur ?
Codominance occurs when two different alleles occur for a gene - both of which are equally dominant
What is the result of codominance ?
Both alleles of the gene are expressed in the phenotype of the organism if present
Give an example of codominance
- The colour of snapdragon flowers
- Two equally dominant alleles exist, each of which codes for the colour of the flower (red and white)
- The three colours that can be produced are red, white and pink
How are alleles represented in codominance ?
- A letter is chosen to represent the gene
- The different alleles are then represented using a second letter which is shown as superscript
What are genes with more than two versions called ?
Multiple alleles
How many alleles can be present in an individual ?
Only two, because there are two versions of the gene (one on each of the homologous chromosomes)
What allele codes for blood group ?
Immunoglobulin gene
What are the different versions of the immunoglobulin gene ?
- Ia
- Ib
- Io
What is the combination of alleles for blood group A ?
IAIA or IAIO
What is the combination of alleles for blood group B ?
IBIB or IBIO
What is the combination of alleles for blood group AB ?
IAIB
What is the combination of alleles for blood group O ?
IOIO
What is the 23rd pair of chromosomes called ?
Sex chromosomes
What do females have on the 23rd chromosome ?
XX
What do males have on the 23rd chromosome ?
- XY
What does the Y chromosome carry ?
- Carries a gene that causes the embryo to develop as a male
- Therefore the sex of the offspring will be determined by whether the sperm fertilising the egg contains a Y chromosome or an X
What are sex linked genes ?
Genes that are carried on the sex chromosomes
Which chromosome is smaller, X or Y ?
Y chromosome is smaller than the X chromosome
What are dihybrid crosses used to show ?
The inheritance of two different characteristics, caused by two genes, which may be located on different pairs of homologous chromosomes
What is dihybrid inheritance ?
Inheritance of two genes
What is the expected result of a heterozygous dihybrid cross ?
9,3,3,1
Why may the actual ratio of results vary from expected ?
- Fertilisation is random
- If there is no crossing over, alleles for 2 characteristics will be inherited together if on the same chromosome
What are linked genes ?
These are genes that are both on the same chromosome
Why may numbers from dihybrid crosses vary from the expected numbers ?
- This is due to the fact that the process is random
- The differences should not be large
What is one of the reasons that the ratios in dihybrid crosses vary largely from what they should be ?
- Linkages
- This means that the genes are located on the same chromosome
What is autosomal linkage ?
- Autosomal linkage refers to when the genes that are linked are found on one of the other pairs of chromosomes
- Any chromosome that isnt a sex chromosome
How are linked genes inherited ?
They are inherited as one unit
What are some examples of linked characteristics ?
Body colour and wing length in fruit flies
What can cause separation of some of the linked genes ?
- Crossing over
- Prophase 1
- Meiosis 1
- Prophase 1
What are genes on the same autosome said to be ?
Linked - this is because they stay together during independent assortment