Introduction to genetics

Introduction to Genetics:

Introduction to Genetics What is genetics? The study of genes and their inheritance as well as variation in living organisms.

Chromosome:

Chromosome Chromosome: a molecular "package" for carrying DNA in cells. Chromosomes come in pairs, called homologous chromosomes, e.g. Human cell nucleus contains 23 pairs. One of each pair comes from the father and other from the mother. DNA is organized as super-coiled double-helical molecules that encode many genes.

GENE:

GENE A segment of DNA that codes for one protein.

Genome:

Genome All the genes in an individual, a population and a species.

Alleles:

Alleles Different versions of same gene, present on a locus on homologous chromosomes. Alleles are dominant when they are expressed and are able to mask the effects of its paired recessive gene. If two alleles codes for same characteristic, they are called homozygous. They can be homozygous dominant (BB-blue coloured eyes). Or homozygous recessive (bb-brown coloured eyes). If two alleles are different they are called heterozygous (Bb). The alleles form Genotype (genetic information) (BB bb or Bb). The alleles, when expressed in an individual are called Phenotype .

The pair of chromosomes are called a “homologous pair,” meaning that they contain corresponding sequences of gene. :

The pair of chromosomes are called a “homologous pair,” meaning that they contain corresponding sequences of gene. Homologous chromosomes contain gene sequences that are similar, but they are not identical copies of each other!

Phenotype:

Phenotype The physical or behavioral traits of an organism, largely determined by the organism's genotype and the environment.

Genotype:

Genotype The complement of alleles present in a particular individual's genome that gives rise to the individual's phenotype.

DNA:

DNA DNA is made up of nucleotide base pairs, deoxyribose sugar and a phosphate group in a form of a super-coiled “double helix” molecule.

Protein:

Protein A linear polymeric molecule made of amino acids linked by peptide bonds.

Monohybrid inheritance:

Monohybrid inheritance The inheritance of single characteristic controlled by only one gene. It involves two alleles of a single gene on homologous chromosomes. For instance, the gene for height has two alleles: tall (T) and dwarf (t). The dominated allele is always showed as a capital letter, which is expressed physically. The recessive allele is written as small letter and is not expressed.

Slide 14:

There are three possible genotypes for height: TT = homozygous tall Tt = heterozygous tall tt = homologous dwarf.

Punnet Squares-monohybrid cross:

Punnet Squares-monohybrid cross Tt x Tt= genotype T t x T t= gametes

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Tt x Tt= genotype T t x T t= gametes Male gametes T t

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Tt x Tt= genotype T t x T t= gametes Male gametes T t Female Gametes T t

Punnet Squares-monohybrid cross:

Punnet Squares -monohybrid cross Tt x Tt= genotype T t x T t= gametes Male gametes T t Female Gametes T t T T

Punnet Squares-monohybrid cross:

Punnet Squares-monohybrid cross Tt x Tt= genotype T t x T t= gametes Male gametes T t Female Gametes T t T T T t

Punnet Squares-monohybrid cross:

Punnet Squares-monohybrid cross Tt x Tt= genotype T t x T t= gametes Male gametes T t Female Gametes T t T T T t t T

Punnet Squares-monohybrid cross:

Punnet Squares-monohybrid cross Tt x Tt= genotype T t x T t= gametes Male gametes T t Female Gametes T t T T T t t T t t

Punnet Squares-monohybrid cross:

Punnet Squares-monohybrid cross Tt x Tt= genotype T t x T t= gametes Male gametes T t Female Gametes T t T T T t t T t t Mendelian Ratios: Genotypic: 1 T T : 2 T t : 1 t t One homozygous Tall: two heterozygous Tall: One homozygous dwarf Phenotypic: 3 dominant: 1 recessive 3 Tall : 1 dwarf

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Some definitions: Genetics is the study of how information is passed on from one generation to the next generation (pattern of inheritance) Inheritance is the passing of characteristics from patents to offspring Monohybrid inheritance is passing of a single character from a single gene from parents to offspring Homologous chromosome: Homologous chromosomes contain similar gene sequences, but they are not identical copies of each other! Genes : Very large molecule carrying code for one character. Allele: Different versions of same gene, present on a locus on homologous chromosomes Dominant allele: A gene that is stronger and expresses itself (Alleles are dominant when they are expressed and are able to mask the effects of its paired recessive gene. Recessive allele: A gene that is weaker and remains recessive Mutation: A change in the structure in the gene, which is expressed Monohybrid cross is a crossbreeding  experiment that follows the inheritance of a single characteristic across one or more generations. Phenotype: The physical or behavioral traits of an organism, largely determined by the organism's genotype and the environment Genotype: If two alleles are different they are called heterozygous (Bb). Homozygous: If two alleles codes for same characteristic, they are called homozygous. They can be homozygous dominant (BB-blue coloured eyes are expressed). Or homozygous recessive (bb-brown coloured eyes are recessive) Heterozygous allele: If two alleles are different they are called heterozygous (Bb).

Monohybrid inheritance:

Monohybrid inheritance Let the allele for round seeds be: R (dominant allele) Let the allele for wrinkled seeds be: r (recessive allele) Parents phenotype round seeds x wrinkled seeds genotype RR rr Gametes F1 generation R R r r F1 phenotypes 100% plants producing round seeds F1 genotypes 100% heterozygotes Rr

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F1 intercross Parents phenotype round seeds x round seeds genotype Rr Rr Gametes F2 generation R r r R Phenotype 75% plants producing round seeds 25% plants producing wrinkled seeds Genotype 25% RR 50% Rr 25% rr Ratio 3:1 Round seeds: wrinkled seeds

Backcross To test whether a plant producing round seeds is homozygous RR or heterozygous Rr it can be crossed with a homozygous rr plant:

Backcross To test whether a plant producing round seeds is homozygous RR or heterozygous Rr it can be crossed with a homozygous rr plant If plant is homozygous dominant RR Parents phenotype round x wrinkled genotype RR rr gametes Offspring If plant is heterozygous Rr Parents phenotype round x wrinkled genotype Rr rr gametes Offspring R R r r R r r r Offspring phenotype 100% round Genotype 100% Rr Offspring phenotype 50% round 50% wrinkled genotype 50% Rr 50% rr