GeneticsGenetics

The study of heredityThe study of heredity

Heredity Heredity – passing traits (characteristics) from passing traits (characteristics) from

parents to their childrenparents to their children– What you see being passed onWhat you see being passed on– Done through the process of meiosis Done through the process of meiosis

and fertilizationand fertilization

GenesGenes

GenesGenes– Information on a Information on a

chromosome that chromosome that codes for specific codes for specific traitstraits

– Come in pairsCome in pairs One from mom and One from mom and

one from dad one from dad

– One is usually more One is usually more powerful than the powerful than the otherother

AllelesAlleles

Different form of the geneDifferent form of the gene– For example:For example:

Trait is heightTrait is height Alleles are tall (T) and short (t)Alleles are tall (T) and short (t)

History of GeneticsHistory of Genetics

Gregor Mendel Gregor Mendel – Austrian MonkAustrian Monk– More than 100 More than 100

years agoyears ago– Worked with pea Worked with pea

plantsplants

Pea PlantsPea Plants

Worked withWorked with– Flower colorFlower color– Flower positionFlower position– Seed colorSeed color– Seed shapeSeed shape– Pod shapePod shape– Pod colorPod color– Stem lengthStem length

Mendel’s gardenMendel’s garden

Types of TraitsTypes of Traits

Dominant Dominant – Traits that are more powerful and are Traits that are more powerful and are

the ones you seethe ones you see– They are represented by capital lettersThey are represented by capital letters

RecessiveRecessive– Traits that are hidden, or covered up, Traits that are hidden, or covered up,

when there is a dominant traitwhen there is a dominant trait– They are represented by lower case They are represented by lower case

letters letters

Representing GenesRepresenting Genes

HomozygousHomozygous– Having 2 identical Having 2 identical

alleles for the same alleles for the same trait trait

– This pea plant This pea plant would be would be represented by the represented by the letters - ttletters - tt

This pea plant is short. It inherited 2 genes for shortness – one from the mom and one from the dad.

Representing GenesRepresenting Genes

Heterozygous-Heterozygous-– Having 2 alleles Having 2 alleles

that are not that are not identical for the identical for the same traitsame trait

– This pea plant This pea plant would be would be represented by the represented by the letters - Ttletters - Tt

This tall pea plant has inherited one tall gene from one parent and one short gene from the other parent

GenotypesGenotypes

An organism’s combination of genes An organism’s combination of genes for a trait is called its genotype for a trait is called its genotype

The genotype is represented by The genotype is represented by letter combinationsletter combinations

The possible choices are 2 capital The possible choices are 2 capital letters, 2 lower case letters or 1 letters, 2 lower case letters or 1 capital letter and 1 lower case lettercapital letter and 1 lower case letter

Examples: TT, tt, TtExamples: TT, tt, Tt

Phenotypes Phenotypes

What an organism looks like as a What an organism looks like as a result of its genes (photograph, result of its genes (photograph, picture)picture)

For example: For example: – A pea plant that is TT would look tall, A pea plant that is TT would look tall, – A pea plant that is Tt would look tall,A pea plant that is Tt would look tall,– A pea plant that is tt would look shortA pea plant that is tt would look short

Punnet SquaresPunnet Squares

Punnet squares are Punnet squares are models used to models used to explain genetic explain genetic crosses crosses

The letters across The letters across the top and down the top and down the left side the left side represent the represent the parents genesparents genes

How do you make a Punnet How do you make a Punnet Square?Square?

Draw a chart with 4 Draw a chart with 4 boxesboxes

Across the top put Across the top put the symbols for the the symbols for the mother’s genotypemother’s genotype

Down the side put Down the side put symbols for the symbols for the father’s genotypefather’s genotype

Here is our exampleHere is our example Now let’s look at the Now let’s look at the

information inside the information inside the boxes. A=purple, a= boxes. A=purple, a= whitewhite

What would the What would the phenotype be for the phenotype be for the letters AA?letters AA?

What would the What would the phenotype be for the phenotype be for the letters Aa?letters Aa?

What would the What would the phenotype be for the phenotype be for the letters aa?letters aa?

Incomplete DominanceIncomplete Dominance

When a heterozygous When a heterozygous genotype (Rr) shows genotype (Rr) shows a new phenotype a new phenotype which is in between which is in between the two parentsthe two parents

A red (RR) A red (RR) snapdragon crossed snapdragon crossed with a white (rr) with a white (rr) snapdragon gives you snapdragon gives you a pink (Rr) a pink (Rr) snapdragonsnapdragon

Incomplete DominanceIncomplete Dominance

The Punnet square The Punnet square example.example.

Note the new Note the new genotypic ratios.genotypic ratios.– 1:2:11:2:1