Section 5-1Section 5-1

What is Genetics?What is Genetics?

I. What have you I. What have you inherited?inherited?

HeredityHeredity is the passing of traits from is the passing of traits from parents to offspringparents to offspring

GenesGenes control traits control traits Genes are segments of DNAGenes are segments of DNA

A. How are traits A. How are traits inherited?inherited?

Genes are found on Genes are found on chromosomeschromosomes in in the the nucleusnucleus of a cell of a cell

When pairs of genes separate into When pairs of genes separate into sex cells during meiosis, pairs of sex cells during meiosis, pairs of genes also separate from one genes also separate from one anotheranother

Each sex cell winds up with one Each sex cell winds up with one form of a gene for each traitform of a gene for each trait

Examples of traits that can be Examples of traits that can be inherited:inherited: Eye colorEye color Hair colorHair color Hair line (straight or widow’s peak)Hair line (straight or widow’s peak)

One sex cell may receive the trait for One sex cell may receive the trait for straight hair line and another sex cell straight hair line and another sex cell may receive the trait for a widow’s may receive the trait for a widow’s peakpeak

The different forms a gene may have The different forms a gene may have for a trait are its for a trait are its allelesalleles

The study of how traits are inherited The study of how traits are inherited is the science of is the science of geneticsgenetics

II. The Father of II. The Father of GeneticsGenetics

The scientific study of traits pass from The scientific study of traits pass from one generation to the next was done by one generation to the next was done by Gregor MendelGregor Mendel

Mendel’s background in Mendel’s background in sciencescience and and mathmath helped him with his studies of helped him with his studies of geneticsgenetics

Mendel studied the inheritance of traits Mendel studied the inheritance of traits in in peapea plants plants

Mendel is known as the Mendel is known as the “Father of “Father of Genetics”Genetics”

III. In Mendel’s gardenIII. In Mendel’s garden

Why did use pea plants in his Why did use pea plants in his experiment?experiment? They are true-breeding – can self-pollinate They are true-breeding – can self-pollinate

and produce identical offspringand produce identical offspring They can also be cross-bred – one plant They can also be cross-bred – one plant

pollinates another to produce a genetic pollinates another to produce a genetic combination in offspringcombination in offspring

An organism that always produces the An organism that always produces the same in its offspring is called a same in its offspring is called a purebredpurebred Example: A tall plant that always produces a Example: A tall plant that always produces a

tall planttall plant

A. Dominant and Recessive A. Dominant and Recessive FactorsFactors

Mendel’s first experiment: cross Mendel’s first experiment: cross pollinated a purebred of tall plants pollinated a purebred of tall plants with a purebred of short plantswith a purebred of short plants

The tall trait is considered a The tall trait is considered a dominantdominant factor because it factor because it dominated or covered up the short dominated or covered up the short factorfactor

The form of the trait that seemed to The form of the trait that seemed to disappear is called the disappear is called the recessiverecessive..

Mendel’s second Mendel’s second experimentexperiment

Self-pollinated the tall offspring and Self-pollinated the tall offspring and planted the seedsplanted the seeds

The results of this experiment were The results of this experiment were in a 3:1 ratio. For every 3 in a 3:1 ratio. For every 3 talltall plants plants there was 1 there was 1 shortshort plant. The plant. The recessive form reappearedrecessive form reappeared

Genotype:Genotype:

B. Predictions Using B. Predictions Using ProbabilityProbability

ProbabilityProbability is a branch of mathematics is a branch of mathematics that helps you predict the chance that that helps you predict the chance that something will happensomething will happen

What made Mendel’s predictions What made Mendel’s predictions accurate?accurate? He produced a large number of plantsHe produced a large number of plants

By increasing the numbers, Mendel By increasing the numbers, Mendel increased his chance of seeing a increased his chance of seeing a predicted 3-to-1 ratiopredicted 3-to-1 ratio

IV. Using a Punnett IV. Using a Punnett SquareSquare

A handy tool used to predict results in A handy tool used to predict results in Mendelian genetics is a Mendelian genetics is a Punnett squarePunnett square

A dominant trait is written with a A dominant trait is written with a capitalcapital letter and a recessive trait is letter and a recessive trait is written with a written with a lower caselower case letter. The letter. The letters show the genetic makeup of an letters show the genetic makeup of an organism called the organism called the genotypegenotype Phenotype refers to the physical Phenotype refers to the physical

appearance of the traitappearance of the trait

A. Alleles determine A. Alleles determine traitstraits

Most cells in your body have two Most cells in your body have two allelesalleles for every traitfor every trait

An organism with two alleles for a trait An organism with two alleles for a trait that are exactly the same is called that are exactly the same is called homozygoushomozygous (TT, tt) (TT, tt)

An organism that has two different alleles An organism that has two different alleles for a trait is called for a trait is called heterozygousheterozygous (Tt) (Tt)

The genotype determines an organisms The genotype determines an organisms physical traits called the physical traits called the phenotypephenotype

B. Determining genotypes B. Determining genotypes and phenotypesand phenotypes

In a Punnett square, the letters In a Punnett square, the letters representing the two alleles from one representing the two alleles from one parentparent are written along the top of the are written along the top of the square and the alleles from the other square and the alleles from the other parentparent are written along the side of the are written along the side of the squaresquare

The letters that you filled in each The letters that you filled in each square represent the possible square represent the possible genoytypesgenoytypes for the for the offspringoffspring the parents the parents could producecould produce

C. Mendel’s successC. Mendel’s success

Mendel succeeded in describing how Mendel succeeded in describing how inherited traits are transmitted from inherited traits are transmitted from parentparent to to offspringoffspring

3 summary statements:3 summary statements: Traits are controlled by alleles on Traits are controlled by alleles on

chromosomeschromosomes An allele’s effect is dominant or recessiveAn allele’s effect is dominant or recessive When a pair of chromosomes separates When a pair of chromosomes separates

during meiosis, the different alleles for a during meiosis, the different alleles for a trait move into separate sex cellstrait move into separate sex cells