Introduction to Introduction to GeneticsGenetics

Mr. ClickMr. Click

77thth Grade Life Science Grade Life Science

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

GeneticsGenetics is the study of is the study of heredity.heredity.

Gregor MendelGregor Mendel is known as is known as the “Father of Genetics.”the “Father of Genetics.”

Who was Mendel?Who was Mendel?Mendel was a monk who lived in a Mendel was a monk who lived in a

monastery in Austriamonastery in AustriaHe spent a lot of time gardening He spent a lot of time gardening

and became interested in why and became interested in why plants looked the way that they plants looked the way that they did.did.

Mendel studied the characteristics Mendel studied the characteristics of pea plants to see how traits of pea plants to see how traits were passed from parents to were passed from parents to offspring.offspring.

Mendel’s DiscoveryMendel’s DiscoveryMendel noticed that some Mendel noticed that some

traits showed up more often traits showed up more often than others. He called these than others. He called these traits: traits: - - DominantDominant – they will cover up – they will cover up another trait that is present.another trait that is present.- - Recessive Recessive traits are the traits traits are the traits that get covered up. You only that get covered up. You only see recessive traits if you get see recessive traits if you get one from each of your parents.one from each of your parents.

GenesGenes are the sections of are the sections of DNA that carry information DNA that carry information about a certain trait.about a certain trait.

The different forms of a trait The different forms of a trait (whether it is dominant or (whether it is dominant or recessive) are called recessive) are called allelesalleles..Dominant alleles are always Dominant alleles are always

shown with a shown with a capital lettercapital letter..Recessive alleles are always Recessive alleles are always

shown with a shown with a lower case letterlower case letter..

Genes: Genes: a reviewa review GenesGenes are the basic unit of heredity are the basic unit of heredity Each chromosome contains many Each chromosome contains many

genes that code for different genes that code for different traitstraits..

Eye colorGene

Eye colorGene

Hair colorGene

Hair colorGene

Alleles are represented with a Alleles are represented with a genotypegenotype – a letter – a letter combination.combination.If the two letters in a genotype If the two letters in a genotype

are the same, it is said to be are the same, it is said to be homozygoushomozygous Ex: HH, hh Ex: HH, hh

If the two letters are different If the two letters are different (one capital, one lower case), it is (one capital, one lower case), it is said to be said to be heterozygousheterozygous. Ex. Hh. Ex. Hh

The The phenotypephenotype is the physical is the physical appearance of a trait.appearance of a trait.

GenesGenesGenes are like committee members; Genes are like committee members;

all of the genes (the all of the genes (the genotypegenotype) sit ) sit down together at a table and decide down together at a table and decide what the organism is going to look what the organism is going to look like (the like (the phenotypephenotype))

GenotypeGenotypeEach gene has an opinion (an Each gene has an opinion (an alleleallele).).When all of the genes are together When all of the genes are together

at the table, they state what their at the table, they state what their opinion is (what allele they are).opinion is (what allele they are).

Allele:Allele:Think of alleles as different Think of alleles as different

flavors of genesflavors of genes

GenotypeGenotype

A

aC

bc

B

Dominant AllelesDominant AllelesGenes have different personalitiesGenes have different personalitiesSome genes are Some genes are loud and bossyloud and bossy. .

They are always convinced that their They are always convinced that their ideas are the best, and they have to ideas are the best, and they have to express them to everyone!express them to everyone!

We say that these genes are We say that these genes are dominant allelesdominant alleles

Dominant alleles are written with Dominant alleles are written with capital letters.capital letters.

Recessive AllelesRecessive AllelesSome genes are Some genes are very shyvery shy. They stare . They stare

at their feet and just mumble at their feet and just mumble something whenever they are asked a something whenever they are asked a question. They might have some cool question. They might have some cool ideas, but they are afraid that they’ll ideas, but they are afraid that they’ll be laughed at if they tell the dominant be laughed at if they tell the dominant genes about them, so they keep quiet.genes about them, so they keep quiet.

We say that these genes are We say that these genes are recessive recessive allelesalleles

Recessive alleles are written with Recessive alleles are written with lower-case letterslower-case letters

PhenotypePhenotypePhenotypePhenotype- Any observable trait or - Any observable trait or

characteristic of an organismcharacteristic of an organismWhen the committee is deciding on When the committee is deciding on

what the animal will look like what the animal will look like ((phenotypephenotype), the genes split up into ), the genes split up into little sub-committees for each trait.little sub-committees for each trait.

A subcommittee consists of only A subcommittee consists of only the copy of the gene from the copy of the gene from Mom and the copy Mom and the copy of the gene from Dad.of the gene from Dad.

PhenotypePhenotypeThese two genes might discover that These two genes might discover that

they are identical and they both they are identical and they both agree that the exact same thing agree that the exact same thing should be done.should be done.

This means the two alleles are This means the two alleles are homozygoushomozygousa a

We will express a

A A

We will express A

PhenotypePhenotypeThese two genes might discover that These two genes might discover that

they are different alleles. Each gene they are different alleles. Each gene has a different idea about how the has a different idea about how the trait should turn out.trait should turn out.

This means the two alleles are This means the two alleles are heterozygousheterozygous

In this case:In this case: When the decisions are made When the decisions are made about what the animal will look like,about what the animal will look like,you see only the dominant gene's ideasyou see only the dominant gene's ideas..

A a

We will express A

Practice:Practice:Assume the following:Assume the following:

C: Straight hairC: Straight hairc: Curly hairc: Curly hair

A person who has curly hair has what A person who has curly hair has what genotypegenotype? ?

A person who has a genotype of Cc A person who has a genotype of Cc has what has what phenotypephenotype??

PracticePractice

For each genotype below, indicate For each genotype below, indicate whether it is heterozygous whether it is heterozygous (He) or (He) or homozygous homozygous (Ho)(Ho)

AA _____ Ee ____ Ii _____ Mm _____AA _____ Ee ____ Ii _____ Mm _____

Bb _____ ff ____ Jj _____ nn _____Bb _____ ff ____ Jj _____ nn _____

Cc _____ Gg ____ kk _____ oo _____Cc _____ Gg ____ kk _____ oo _____

DD _____ HH ____ LL _____ Pp _____DD _____ HH ____ LL _____ Pp _____

PracticePractice

For each of the For each of the genotypes below genotypes below determine what phenotypes determine what phenotypes would be possible.would be possible.

Purple flowers are dominant to white Purple flowers are dominant to white flowers.flowers.PP___________________PP___________________Pp___________________Pp___________________pp___________________pp___________________

Bobtails in cats are recessive.Bobtails in cats are recessive.TT _________________TT _________________Tt _________________Tt _________________tt________________tt________________

Brown eyes are dominant to blue Brown eyes are dominant to blue eyeseyesBB_________________BB_________________Bb________________Bb________________bb________________bb________________

For each phenotype below, list For each phenotype below, list the genotypes (remember to use the genotypes (remember to use the letter of the dominant trait)the letter of the dominant trait)

Straight hair is dominant to curly.Straight hair is dominant to curly._____ straight_____ straight_____ curly_____ curly

Pointed heads are dominant to round Pointed heads are dominant to round heads.heads. _____ pointed_____ pointed _____ round_____ round

Helpful Video from Khan Helpful Video from Khan AcademyAcademy

For help with Punnett Squares go to:For help with Punnett Squares go to:http://www.youtube.com/watch?v=eEUvRrhmcxM

Punnett SquaresPunnett SquaresSet up the Punnet squares for each Set up the Punnet squares for each

of the crosses listed below.of the crosses listed below.Normal height plants are dominant to Normal height plants are dominant to

dwarf plants.dwarf plants.RR x rrRR x rr

What percentage of the offspring will What percentage of the offspring will be normal height?_________________be normal height?_________________

Punnett SquaresPunnett SquaresSet up the Punnet squares for each of Set up the Punnet squares for each of

the crosses listed below.the crosses listed below.Normal height plants are dominant to Normal height plants are dominant to

dwarf plants.dwarf plants.Rr x RrRr x Rr

What percentage of the offspring will What percentage of the offspring will be normal height?_________________be normal height?_________________

Punnett SquaresPunnett SquaresSet up the Punnet squares for each of Set up the Punnet squares for each of

the crosses listed below.the crosses listed below.Normal height plants are dominant to Normal height plants are dominant to

dwarf plants.dwarf plants.Rr x rrRr x rr

What percentage of the offspring will What percentage of the offspring will be normal height?_________________be normal height?_________________

Punnett SquaresPunnett SquaresSet up the Punnet squares for each of Set up the Punnet squares for each of

the crosses listed below.the crosses listed below.Normal height plants are dominant to Normal height plants are dominant to

dwarf plants.dwarf plants.RR x RrRR x Rr

What percentage of the offspring will What percentage of the offspring will be normal height?_________________be normal height?_________________

A TT (tall) plant is crossed with a tt A TT (tall) plant is crossed with a tt (short plant). (short plant). What percentage of the offspring will be What percentage of the offspring will be

tall? ___________tall? ___________A Tt plant is crossed with a Tt plant.A Tt plant is crossed with a Tt plant.

What percentage of the offspring will be What percentage of the offspring will be short? ______short? ______

A heterozygous round seeded plant A heterozygous round seeded plant (Rr) is crossed with a homozygous (Rr) is crossed with a homozygous round seeded plant (RR).round seeded plant (RR).What percentage of the offspring will be What percentage of the offspring will be

homozygous (RR)? __________homozygous (RR)? __________

Note 44) Mendel’s Laws of Note 44) Mendel’s Laws of GeneticsGenetics

Mendel’s Law of SegregationMendel’s Law of Segregation states states that because of meiosis, each gamete that because of meiosis, each gamete that is made only only receives 1 copy that is made only only receives 1 copy of each gene.of each gene.

Mendel’s Law of Independent Mendel’s Law of Independent Assortment Assortment states that the alleles of states that the alleles of different genes sort independently of different genes sort independently of each other during meiosis. In other each other during meiosis. In other words, inheriting one trait cannot words, inheriting one trait cannot influence another trait.influence another trait.

Mendel’s Law of DominanceMendel’s Law of Dominance states states that if you have a heterozygous that if you have a heterozygous organism, you will only see the organism, you will only see the dominant trait and the recessive will dominant trait and the recessive will be hidden.be hidden.