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Inheritance
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Inheritance exam notes for iGCSE
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3.14 understand gene and genomeGENOME: all genetic information (DNA) of an organism
GENE: Heritable factor that consists of a section of DNA that codes for a specific Proteins to influence
specific characteristics. They are found on chromosomes- in the nucleus of a cell.
- A gene can affect a phenotype of an organism
- A gene codes for a single protein
- The protein affects the phenotype through a
particular mechanism
- The phenotype of an individual can also be
affected by the environment
3.19 understand how genes exist in alternative forms called alleles
- Sometimes more than one version of a gene occurs= alleles (we all have the gene for iris pigment (protein),
but there are different colors of iris pigment, same gene but different alleles)
- Alleles give rise to a range of different inherited characteristics in a population (eye color, blood type…)
3.20 understand the meaning of these terms
DOMINANT A gene allele that ‘expresses’ over another allele in homozygous and heterozygous pairs.
Shown in phenotype.
RECESSIVE A gene allele that only ‘expresses’ when it is matched with another recessive allele and
never when matched with a dominant allele. Shown in phenotype
HOMOZYGOUS Both alleles are the same alleles at corresponding chromosomal Loci. (BB or bb)
HETEROZYGOUS The 2 alleles are different (Bb)
PHENOTYPE This is the characteristic that appears (blue
eyes, brown hair…)
GENOTYPE This is the particular gene combination (BB,
Bb, bb)
3.22 understand that most phenotypic features are the result of polygenic inheritance rather than single genes
POLYGENIC INHERITANCE
Multifactorial inheritance; quantitative inheritance. The determination of a particular characteristic,
e.g: height or skin color, by many genes (polygenes), each having a small effect individually. Characteristics
controlled in this way show continuous variation.
, Human phenotypes such as hair color, eye color, height, and weight are examples of polygenic traits.
3.23 describe patterns of monohybrid inheritance using a genetic diagram
GENERATIONS There are the parents, then their offspring, and their offspring, etc. etc.
Each generation has a name
- The first plants or animals bred together are called the Parental generation, or P1 generation.
- Their offspring are called the First Filial generation, or F1 generation.
- Their offspring are called the Second Filial generation, or F2 generation (etc)
PUNNETT SQUARES CROSSING
3.25 predict probabilities of outcomes from monohybrid crosses
3.26 understand how the sex of a person is controlled by one pair of chromosomes
Humans have 46 chromosomes (2 of them are sex) The diploid number of
chromosomes is 46 (2n)
and the haploid number is
23 (n)
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