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11932493
Inherited Change
Beschreibung
A2 Biology (Section 7) Mindmap am Inherited Change, erstellt von Dominic Weston am 18/01/2018.
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biology
section 7
a2
Mindmap von
Dominic Weston
, aktualisiert more than 1 year ago
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Erstellt von
Dominic Weston
vor mehr als 6 Jahre
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Zusammenfassung der Ressource
Inherited Change
Inheritance
Phenotype
Expression of characteristic due to genotype
Phenotype can be altered and is due to the environment
Any changes to the phenotype is a modification and is not inherited by offspring
Genotype
Genetic constitution of an organism
Any change to genotype must be from mutations in the DNA
Mutations are inherited by offspring
Gene
Length of DNA that can code for a polypeptide
Can also code for rRNA and tRNA
Alleles are different forms of a gene
Locus is the position of a gene on a DNA molecule
Two dominant/recessive alleles
Homozygous dominant/recessive
One of each dominant and recessive alleles
Heterozygous
Humans are diploid organisms containing 2 sets of chromosomes
Two alleles for each gene
Gametes contain one allele for each gene
Double when fuse during fertilisation
Monohybrid Inheritance
Basic law of Genetics
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
Inheritance of a single gene
3:1 ratio
Pure-breeding
If identical and bred together
Two alleles are the same for a gene
Homozygous
If two pure breds are crossed then the phenotype will be which ever has the dominant allele
Dihybrid Inheritance
Study of how more than one characteristic is inherited
Two characteristics, R/r and G/g
Parent 1 RrGg
Set of Gametes
RG
Rg
rG
rg
Parent 2 RrGg
9:3:3:1 Ratio
Codominace
Both alleles expressed in the phenotype - both dominant
Multiple alleles
When there are more than two alleles of the same gene
Arise from mutations
At different positions in the gene
Blood groups are an example
I^O is recessive
I^A is Codominant with I^B
So a heterozygous I^A would have to be I^AI^O
I^A
I^B
I^AB
I^O
Increases number of possible phenotypes
If not ratio of 3:1 or 9:3:3:1 between two heterozygous parents then the gene is codominant
Sex-linkage
Characteristics are said to be sex-linked when the allele that codes for it is found on a sex chromosome
Sex chromosomes
Male XY
Female XX
Y chromosome smaller than X so carries fewer genes
Most of the genes carried on X chromosome (X-linked)
Males often only have one allele for sex linked genes
One copy means that allele is always expressed, even if recessive
Males more likely to suffer from X-linked disorders
E.g. haemophilia and colourblindness
Females are likely carriers
Ratios change depending on parents - carriers / normal
3:1 / 2:1:1
Autosomal Linkage
Any two genes that occur on the same chromosome are said to be linked
On the same autosome, won't be separated during meiosis
Alleles will be passed on to offspring
Unless crossing over splits them first
All chromosomes that aren't sex chromosomes are autosomes
The closer the two genes are on the autosome the more closely they are said to be linked
Closer they are less likely to be split
If two genes are autosomally link they will not give the expected phenotypic ratio
Autosomal alleles inherited together, give higher proportion of offspring will have their parents genotype and phenotype
Used to predict phenotypic ratio to identify the autosomal link
Cross two parents to find offspring
Back cross with parent and offspring to expect 1:1:1:1
Instead get a different ratio - e.g. 8:1:1:8
As the two 8's genotypes are so common they must be linked in the parent
The two 8's gametes were mainly produced by parent, others still produced due to cross over
As a result higher proportion of offspring have parents' phenotypes
Epistasis
Where the phenotype of one gene masks the phenotype of a second gene
For example, baldness masks hair colour
Also where a gene can control / effect anothers apperance
Results in a reduction in the number of possible phenotypes in offspring
Dominant Epistasis
12:3:1
Recessive Epistasis
Normal 9:3:3:1
Reduced from normal 4, to epistasis 3 phenotypes
9:4:3
Chi-squared
A math tool used to determine whether observed results match the expected theoretical results, showing they are significantly different
Used for categorical data
To see if the results support a theory use a null hypothesis
Always states there's no significant difference
Tests if results are different due to chance or incorrect theory
x^2 will either support or reject the null hypothosis
Pedigree Diagrams
Medienanhänge
Chi Squared (binary/octet-stream)
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