Summary

Summary Topic 7: Genetics, populations, evolution and ecosystems

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Module
Topic 7: Genetics, populations, evolution

Institution
AQA

Topic 7: Genetics, populations, evolution and ecosystems 3.7.1 Inheritance The genotype is the genetic constitution of an organism. All of the alleles that an organism carries on its chromosomes The phenotype is the expression of this genetic constitution and its interaction with the environmen...

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3.7.1 Inheritance

The genotype is the genetic constitution of an organism.

● All of the alleles that an organism carries on its chromosomes

The phenotype is the expression of this genetic constitution and its
interaction with the environment.

● observable characteristics of an organism which the result of the genotype as well
as environmental factors

There may be many alleles of a single gene.

● alleles are an alternative form of a gene
● Locus is specific position of gene on chromosome
● Two alleles for the gene both found at same loci on homologous pairs of
chromosomes

Alleles may be dominant, recessive or codominant.

● Dominant
○ only a single allele requires for characteristic to be expressed in the
phenotype
○ whether organism only has one dominant allele (trait will be expressed)
■ heterozygous dominant
○ whether organism has two dominant alleles (trait will be expressed)
■ homozygous dominant
● Recessive
○ characteristic only expressed if there is no dominant allele present
■ must be two recessive alleles present in order for the phenotype to be
expressed

, ■ homozygous recessive
● Codominant
○ both alleles expressed equally and contribute to the phenotype
○ either blend of two characteristic or both characteristics being seen together

In a diploid organism, the alleles at a specific locus may be either
homozygous or heterozygous.

The use of fully labelled genetic diagrams to interpret, or predict,

the results of:

• monohybrid and dihybrid crosses involving dominant, recessive and
codominant alleles

● Monohybrid inheritance looks at how the alleles for a single gene are passed on
from one generation to the next
● Known information about the genotypes, phenotypes and the process of meiosis are
used to make predictions about the phenotypes of offspring that would result from
specific breeding pairs
● When two individuals sexually reproduce there is an equal chance of either allele
from their homologous pair making it into their gametes and subsequently the
nucleus of the zygote
○ This means there is an equal chance of the zygote inheriting either allele
from their parent
● Genetic diagrams are often used to present this information in a clear and precise
manner so that predictions can be made
○ These diagrams include a characteristic table called a Punnett square
● The predicted genotypes that genetic diagrams produce are all based on chance
○ There is no way to predict which gametes will fuse so sometimes the
observed or real-life results can differ from the predictions

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Summary Topic 7: Genetics, populations, evolution and ecosystems

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