3918161
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Mind Map by benhay61, updated more than 1 year ago
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Created by Eilidh Young
over 8 years ago
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Copied by benhay61
over 8 years ago
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SOURCES OF VARIATION IN A GENE POOL
- Mutation
- A mutation is a permanent change in the base sequence of DNA
- Mutations can be: 1. silent, 2. harmful, 3. beneficial
- Somatic mutations can't enter gene pool
- Mutations can occur during DNA replication or from mutagens
- A mutation is a permanent change in the base sequence of DNA
- Independent Assortment
- When homologous pairs of chromosomes line up during meiosis, they do so randomly
- This means it is completely random
which combination of alleles ends up
in a particular gamete
- This means it is completely random
which combination of alleles ends up
in a particular gamete
- When homologous pairs of chromosomes line up during meiosis, they do so randomly
- Segregation
- Pairs of alleles are segregated when the homologous
chromosomes split so that each gamete receives one allele
- Segregation results in all daughter cells being unique
- Segregation results in all daughter cells being unique
- Pairs of alleles are segregated when the homologous
chromosomes split so that each gamete receives one allele
- Crossing Over
- Occurs when homologous pairs of chromosomes line up on cell
equator and parts of neighbouring chromosomes cross over
- These sections are then exchanged and each gamete
produced has a different combination of alleles
- These sections are then exchanged and each gamete
produced has a different combination of alleles
- Occurs when homologous pairs of chromosomes line up on cell
equator and parts of neighbouring chromosomes cross over
- Dihybrid Inheritance
- Dihybrid crosses involve two genes, and four alleles
- These genes are linked if they are on the same chromosome,
and the closer together they are on the chromosome, the
less likely they will be separated during crossing over
- They will therefore be inherited together and reduce the
number of possible combinations of alleles in gametes
- They will therefore be inherited together and reduce the
number of possible combinations of alleles in gametes
- Where there is no linkage
expected phenotype ratio is 9:3:3:1
- Where this is not the case the genes are most likely linked
- Where this is not the case the genes are most likely linked
- These genes are linked if they are on the same chromosome,
and the closer together they are on the chromosome, the
less likely they will be separated during crossing over
- Dihybrid crosses involve two genes, and four alleles
- Monohybrid Inheritance
- Co-dominance
- Where a single gene has more
than one dominant allele
- An organism heterozygous for both dominant alleles
with have both expressed in the phenotype (MIXTURE)
- An organism heterozygous for both dominant alleles
with have both expressed in the phenotype (MIXTURE)
- Where a single gene has more
than one dominant allele
- Multiple Alleles
- Multiple alleles exist due to mutations in a
single gene resulting in more than two
alleles for that gene e.g. human blood type
- Multiple alleles exist due to mutations in a
single gene resulting in more than two
alleles for that gene e.g. human blood type
- Lethal Alleles
- Lethal alleles code for a phenotype
that causes the death of an organism
- Changes expected phenotype ratio
- Changes expected phenotype ratio
- It usually arises as a result of a mutation in an
essential gene cauusing the gene to no longer
produce a functioning version of an essential protein
- Lethal alleles code for a phenotype
that causes the death of an organism
- Incomplete Dominance
- Where in a single gene the two alleles
are not dominant over each other
- The resulting phenotype is a BLEND of the two alleles
- The resulting phenotype is a BLEND of the two alleles
- Where in a single gene the two alleles
are not dominant over each other
- Co-dominance
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