AQA A-Level Biology Paper 2
Alleles that are neither dominant nor recessive to one another, so both alleles are always
expressed in the phenotype.
Codominant
The inheritance of a single gene
Monohybrid inheritance
Brainpower
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Physical, behavioural, biochemical expression of an organisms genotype
Phenotype
The type of genes an individual has
Genotype
Alles that is always expressed in the phenotype
Dominant
,Only expressed in the phenotype when homozygous
Recessive
both alleles are the same
Homozygous
Both alleles for a specific gene are different
Heterozygous
Position of a gene on a chromosome
Loci
A set of instructions for a specific polypeptide
Gene
Different forms of a gene
Allele
1. Expected ratios are probability
2. Sexual reproduction is random due to random fusion of gametes and random assortment
homologous chromosomes.
3. Small sample size
4. Linked genes
Suggest four reasons why observed ratios are not the same as expected ratios (4).
1. Homologous chromosomes pair up
2. Crossing over / chiasmata form;
3. Produces new combination of alleles
4. Chromosomes separate at random
5. This produces varying combinations of genes
, 6. Chromatids separated at meiosis II
Meiosis results in cells that have the haploid number of chromosomes and show genetic
variation. Explain how. (6)
1. Refer to the specific individuals (using their number)
2. Explain what happened with the genes (passed on recessive/dominant)
3. Describe the genotype of your examples and mention their phenotype
(homozygous/heterozygous etc)
Pedigree Questions Mark Scheme (3)
Group of organisms of the same species occupying a particular space at a particular time that
can potentially interbreed to produce fertile offspring.
Populations
The total number of genes of every individual in an interbreeding population.
Gene pool
How often an allele appears in a population.
desired allele/total alleles = allele frequency (decimal form)
Allele frequency [definition][Equation] (2)
No emigration or immigration
No mutations
Mating is random
No natural selection
Hardy-Weingberg Assumptions (4)
1. Selection pressure exists in an environment (name it)
2. Variation exists in stated phenotype of organism/ mutation occurs creating new alleles
3. Some individuals have the selective advantage (describe it)
4. Produces differential survival/ organisms with successful alleles more likely to survive
Alleles that are neither dominant nor recessive to one another, so both alleles are always
expressed in the phenotype.
Codominant
The inheritance of a single gene
Monohybrid inheritance
Brainpower
Read More
Previous
Play
Next
Rewind 10 seconds
Move forward 10 seconds
Unmute
0:00
/
0:15
Full screen
Physical, behavioural, biochemical expression of an organisms genotype
Phenotype
The type of genes an individual has
Genotype
Alles that is always expressed in the phenotype
Dominant
,Only expressed in the phenotype when homozygous
Recessive
both alleles are the same
Homozygous
Both alleles for a specific gene are different
Heterozygous
Position of a gene on a chromosome
Loci
A set of instructions for a specific polypeptide
Gene
Different forms of a gene
Allele
1. Expected ratios are probability
2. Sexual reproduction is random due to random fusion of gametes and random assortment
homologous chromosomes.
3. Small sample size
4. Linked genes
Suggest four reasons why observed ratios are not the same as expected ratios (4).
1. Homologous chromosomes pair up
2. Crossing over / chiasmata form;
3. Produces new combination of alleles
4. Chromosomes separate at random
5. This produces varying combinations of genes
, 6. Chromatids separated at meiosis II
Meiosis results in cells that have the haploid number of chromosomes and show genetic
variation. Explain how. (6)
1. Refer to the specific individuals (using their number)
2. Explain what happened with the genes (passed on recessive/dominant)
3. Describe the genotype of your examples and mention their phenotype
(homozygous/heterozygous etc)
Pedigree Questions Mark Scheme (3)
Group of organisms of the same species occupying a particular space at a particular time that
can potentially interbreed to produce fertile offspring.
Populations
The total number of genes of every individual in an interbreeding population.
Gene pool
How often an allele appears in a population.
desired allele/total alleles = allele frequency (decimal form)
Allele frequency [definition][Equation] (2)
No emigration or immigration
No mutations
Mating is random
No natural selection
Hardy-Weingberg Assumptions (4)
1. Selection pressure exists in an environment (name it)
2. Variation exists in stated phenotype of organism/ mutation occurs creating new alleles
3. Some individuals have the selective advantage (describe it)
4. Produces differential survival/ organisms with successful alleles more likely to survive
