BIO207H5 Chapter Notes - Chapter 2: Pea, Punnett Square, Mendelian Inheritance

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Published on 19 Apr 2013
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Chapter 2 - Mendelian Genetics
Principal Points
- The genotype is the genetic makeup of an organism, whereas the phenotype
is the observable characteristic (produced by interaction b/w genotype
environment)
- Genes provide the potential for the development of characteristics; this
potential can be affected by interactions with other genes and with the
environment
- PRINCIPLE OF SEGREGATION – two members of gene pair segregate from
each other in the formation of gametes
- PRINCIPLE OF INDEPENDENT ASSORTMENT – members of different gene pairs
are transmitted independently of one another during gamete production
- To determine an unknown genotype (usually individual with dominant
phenotype), a TEST CROSS is made with a homozygous recessive individual,
that tells the genotype of unknown
Genotype and Phenotype
- HEREDITY TRAITS are transmitted from one generation to another (aka
characters)
- These traits are controlled by genes
- Genes provide potential for developing a particular phenotypic characteristic
- Genes are a starting point for determining the structure and function of an
organism and the route to the mature phenotypic state is highly complex,
involving many interacting biochemical pathways
- Actions of other genes and products + Genotype + Environmental influences
and random developmental events Phenotype (expression of physical trait)
Mendel’s Experimental Design
- Mendel cross-bred pea plants PISUM SATIVUM for its characteristics such as
colour, shape etc
- For a Genetic Cross: Two diploid individuals differing in phenotype are
allowed to produce haploid gametes by meiosis. Fusion of male and female
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gametes produces zygotes from which the diploid progeny individuals are
generated. The phenotypes of the offspring are analyzed to provide clues to
heredity of those phenotypes
- SELF-FERTILIZATION/SELFING – anthers at the ends of the stamen produce
pollen (male gametophyte) which lands on the pistil (female gametophyte)
within the same flower, thus fertilizing the plant
- CROSS-FERTILIZATION/CROSS – fusion of male gametes (pollen) and female
gametes (eggs) of two different plants
- Mendel worked with TRUE BREEDING/PURE BREEDING STRAINS – the
characteristics stay unchanged from parents to offspring over generations
- Mendel studied seven characteristics: flower and seed coat colour, seed
colour, seed shape, pod colour, pod shape, stem height, and flower position.
Monohybrid Crosses and Mendel’s Principle of Segregation
- P GENERATION – parental generation
- F1 – First filial generation
- MONOHYBRID CROSS – crosses between true-breeding strains of peas that
differed in a single trait.
oExample: cross smooth seed plants with wrinkled seed plants
- RECIPRICAL CROSS – when the parental traits are switched such as male with
smooth seed becomes female with smooth seeds, while female with wrinkled
seed becomes smooth male
- PRINCIPLE OF UNIFORMITY in F1 – all offspring in the first generation are alike
- Mendel found that F1 generation may all be same phenotype, but they did not
breed true i.e. they had different genome
- Each factor (gene) exists in alternative forms, called ALLELES
- DOMINANT is the allele that is able to express its trait in the phenotype of the
F1
- RECESSIVE is the allele whose trait is not expressed in the phenotype of the
F1
- True-breeding individuals that contain the same specific allele for a particular
gene are said to be HOMOZYGOUS for that gene
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Document Summary

The genotype is the genetic makeup of an organism, whereas the phenotype is the observable characteristic (produced by interaction b/w genotype environment) Genes provide the potential for the development of characteristics; this potential can be affected by interactions with other genes and with the environment. Principle of segregation two members of gene pair segregate from each other in the formation of gametes. Principle of independent assortment members of different gene pairs are transmitted independently of one another during gamete production. To determine an unknown genotype (usually individual with dominant phenotype), a test cross is made with a homozygous recessive individual, that tells the genotype of unknown. Heredity traits are transmitted from one generation to another (aka characters) Genes provide potential for developing a particular phenotypic characteristic. Genes are a starting point for determining the structure and function of an organism and the route to the mature phenotypic state is highly complex, involving many interacting biochemical pathways.

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