Topic 7 A: Genetics Flashcards
Definition of gene?
Dna base sequences that code for polypeptides.
Definition of alleles?
Different versions of a gene.
Definition of Loci?
Fixed position on chromosome where allele is found.
Definition of genotypes?
The alleles an individual has for a particular characteristic.
Definition of phenotype?
Observable/biochemical characteristics of an organism which can be affected by the environment.
Definition of homozygous?
Alleles are the same on both chromosomes.
Definition of heterozygous?
Different alleles on each chromosome.
Definition of dominant?
Only one copy of alleles is needed for characteristics to show.
Definition of recessive?
Two copies of an allele are needed for characteristic to present itself.
Definition of co-dominant?
Both alleles contribute to a phenotype (either blend or both represent seperately).
Definition of multiple alleles?
Genes contain more than two alleles.
Definition of monohybrid inheritance?
Inheritance of a single gene.
Definition of dihybrid inheritance?
e.g., parents are both AaBb
When two characteristics are inherited from two different genes which have different alleles at the same time.
Definition of pure breeding?
e.g., parent 1 = bb and parent 2 = BB
Organisms are homozygous for particular gene.
Definition of first filial generation (F1)?
First generation of pure breeds.
What is the ratio within the F2 generation?
3:1
What is the law of segregation?
In diploid organisms, characteristics are determined by alleles that occur in pairs. Only one of each pair of alleles can be present in a single gamete.
Why are ratios not always as expected? (2)
- fertilisation of gametes is random.
- samples have been taken from small population, not representative.
Ratio between dihybrid heterozygous parents?
e.g., Parent 1 = SsYy and Parent 2 = SsYy
9:3:3:1
How are genotypes written when alleles are co-dominant?
Superscript the allele.
Example: what are the genotypes of a co-dominant red cow and a co-dominant white cow?
coat colour = C
red colour = C^r
white colour = c^w
What is the ratio of two homozygous parents containing co-dominant alleles?
100% mix.
What is the ratio of two heterozygous parents containing co-dominant alleles?
1 : 2 : 1
Multiple allele crosses example?
Blood groups:
- blood group A = I^A (dominant)
- blood group B = I^B (dominant)
- blood group AB = I^A I^B
- blood group O = I^O (recessive)
Male and female sex chromosomes?
Male = XY
Female = XX
What are sex-linked traits?
Traits inherited on the X or Y chromosome (most on the X chromosome).
Difference between X and Y chromosomes?
Y is smaller
Y contains less genes
Only males have the Y chromosome
Y only contains genes that makes an individual a male
X chromosome function?
Has genes that make you biologically female and many other functional genes.
Significance of X linked recessive conditions regarding gender?
- men only need one copy of the x-linked recessive allele to get the condition, as they only have one X chromosome.
- females need two copies of the recessive x-linked chromosome for it to be presented, as they have two X chromosomes.
What is haemophilia?
An x-linked recessive condition that hinders blood clotting abilities.
Due to a lack of functional protein (Factor VIII) involved in blood clotting.
How is haemophilia treated?
Given an injection 3x a week containing Factor VIII/ functional protein (genetically engineered to prevent rejection).
Pedigree diagram : give evidence that the condition is sex-linked? (generic question)
Only males have it.
Pedigree diagram : give evidence that the condition is caused by a recessive allele?
Parents without the condition have a child with the condition.
Independent assortment definition?
Random combinations of maternal and paternal chromosomes. (during metaphase 1)
Crossing over definition?
When non-sister chromatids wrap around eachother and swap alleles after chiasmata, providing variation.
Dihybrid inheritance definition?
Inheritance of two chromosomes controlled by two different genes on two chromosomes at the same time.
Autosome?
Chromosome that is not a sex chromosome.
Autosomal linkage?
When two genes are located on the same autosomal chromosome.
What happens to the genes during autosomal linkage?
e.g., if parental genotypes are Gg and Nn - the 2 gametes are GN and gn
- genes stay together during independent assortment in Meiosis 1 and both alleles are passed to offspring together.
- so there are only two allele combinations in the gametes.
Ratio of 2 heterozygous parents during autosomal linkage?
3:1
Recombinants?
Combinations of phenotypes that were not in the original parents (due to crossing over)
Why is the distances between genes on a chromosome significant?
- the further away, the more likely crossing over will occur because there is more space so more chances.
Epistasis?
When the allele of one gene affects or masks the expression of another in the phenotype.
What is the chi-square statistic?
Test that measures how a model compares to the actual observed data.
What is the null hypothesis?
There is no significant difference between two sets of data (e.g., observed and expected) and that any numerical difference from expected values are due to chance alone.
Chi-squared equation?
chi-squared = sum of ( observed numbers - expected numbers)^2 / expected number
cs = sum of (o-e)^2/e
Conditions for chi-squared?
- sample size must be relatively large (20+)
- data must fall into discrete categories
- only raw counts (no percentages etc)
- used to compare experimental results with theoretical ones (e.g., in genetic crosses with expected Mendelian ratios)
What is the degree of freedom?
number of classes - 1
When to reject or accept null hypothesis?
- if probability is less than 5% - difference is significant - reject
- if probability is more than 5% - difference isn’t significant - accept
