Chapter 3: GeneticsChapter 3: GeneticsSection 1: What is Heredity?Section 1: What is Heredity?

The passing of The passing of traitstraits from from parents to parents to offspringoffspring

GeneticsGenetics – the – the scientific study of scientific study of heredityheredity

““Father of Father of Genetics” - Gregor Genetics” - Gregor MendelMendel

Why did Mendel study Peas?Why did Mendel study Peas?

Pea plants have Pea plants have many traits that many traits that exist in only exist in only twotwo forms forms

GardenGarden peas peas produce a large produce a large number of number of offspring in one offspring in one generationgeneration

How did Mendel’s experiments How did Mendel’s experiments work?work?

Mendel crossed Mendel crossed plants with plants with oppositeopposite forms of a forms of a traittrait, for , for example, tall plants example, tall plants and short plantsand short plants

PurebredPurebred – An – An organism that organism that always produces always produces offspring with the offspring with the same form of a trait same form of a trait as the parentas the parent

What other traits did Mendel What other traits did Mendel study?study?

Stem HeightStem Height Seed Seed shapeshape Seed colorSeed color Seed coat colorSeed coat color Pod Pod shapeshape PodPod color color Flower positionFlower position

What are genes and alleles?What are genes and alleles? Genes – A segment Genes – A segment

of of DNADNA on a on a chromosome that chromosome that codes for a specific codes for a specific traittrait

Alleles – the different Alleles – the different forms of a forms of a genegene

Each offspring Each offspring inherits inherits twotwo alleles – alleles – one from each one from each parentparent

What are the types of alleles?What are the types of alleles? DominantDominant – –

An allele whose An allele whose trait always trait always shows up in shows up in the organism the organism when the allele when the allele is present (ex. is present (ex. TT Tt)TT Tt)

RecessiveRecessive – – An allele that is An allele that is maskedmasked when when a dominant a dominant allele is allele is present (tt)present (tt)

What is a Hybrid?What is a Hybrid?

An An organismorganism that has two that has two different different allelesalleles for a for a trait; an trait; an organism that organism that is heterozygous is heterozygous for a particular for a particular trait (Tt)trait (Tt)

How are alleles represented in How are alleles represented in shorthand?shorthand?

Geneticists use Geneticists use lettersletters Dominant allele = Dominant allele = capitalcapital

letter (T)letter (T) Recessive allele = Recessive allele = lowercaselowercase letter (t) letter (t)

Section 2: Probability and GeneticsSection 2: Probability and GeneticsWhat is What is

Probability?Probability?

The The likelihoodlikelihood that a particular that a particular event will occurevent will occur

What is What is likelylikely to to occur; occur; notnot necessarily what necessarily what will occurwill occur

MoreMore trials brings trials brings you closer to the you closer to the actual resultsactual results

How is probability related to How is probability related to genetics?genetics?

Mendel discovered that the Mendel discovered that the mathematical principles of mathematical principles of probabilityprobability applied to his work applied to his work

The principles of probability can The principles of probability can be used to be used to predictpredict the results the results of genetic crossesof genetic crosses

Example: Example: Probability of producing a tall Probability of producing a tall

plant plant 33 in 4 in 4 Probability of producing a Probability of producing a

small plant small plant 11 in 4 in 4

What is a Punnett Square?What is a Punnett Square? A A chartchart that shows that shows

all the possible all the possible combinations of combinations of alleles that can alleles that can result from a result from a geneticgenetic cross cross

They show They show allall the the possible outcomes possible outcomes of a genetic cross of a genetic cross and determine the and determine the probabilityprobability of a of a particular outcomeparticular outcome

How do you read a punnett square How do you read a punnett square to determine genetic probability?to determine genetic probability?

When Mendel When Mendel performed his performed his cross he cross he discovered that discovered that 7575% of the % of the plants had tall plants had tall stems (3 out of stems (3 out of the 4 plants) and the 4 plants) and 2525 % of the % of the plants had short plants had short stems ( 1 of the stems ( 1 of the 4 plants)4 plants)

What are two of the terms What are two of the terms geneticists use to describe geneticists use to describe

organisms?organisms? Phenotype – an Phenotype – an organism’s organism’s physicalphysical appearance, or appearance, or visible traits (Ex. visible traits (Ex. Stem height Stem height phenotype, tall or phenotype, tall or short)short)

Genotype – An Genotype – An organism’s organism’s geneticgenetic makeup, makeup, or allele or allele combinationscombinations

What are two additional terms What are two additional terms geneticists use to describe an geneticists use to describe an

organism?organism? Homozygous – Homozygous –

Having two Having two identicalidentical alleles for a alleles for a trait (Ex: TT, tt)trait (Ex: TT, tt)

Heterozygous – Heterozygous – Having two Having two differentdifferent alleles for a alleles for a trait (Ex: Tt)trait (Ex: Tt)

What term did Mendel use to What term did Mendel use to describe heterozygous pea plants?describe heterozygous pea plants?

HybridHybrid

What is Codominance?What is Codominance?

A condition in A condition in which which neitherneither of two alleles of two alleles of a gene is of a gene is dominantdominant or or recessiverecessive

Found in Found in Erminette Erminette chickens and chickens and cattle cattle

Section 3: The Cell and InheritanceSection 3: The Cell and InheritanceWho is Walter Sutton and what did he Who is Walter Sutton and what did he

discover?discover?

Walter Walter SuttonSutton was was an American an American geneticist whose geneticist whose idea came to be idea came to be known as the known as the chromosome theory chromosome theory of of inheritanceinheritance

GenesGenes are carried are carried from parents to from parents to their offspring on their offspring on chromosomeschromosomes

What is Meiosis?What is Meiosis? The The processprocess that occurs that occurs

in in sexsex cells (sperm and cells (sperm and egg) by which the egg) by which the number of chromosomes number of chromosomes is reduced by halfis reduced by half

There are There are 4646 total total chromosomes in your chromosomes in your body; body; 2323 pairs; 23 came pairs; 23 came from your dad and 23 from your dad and 23 came from your momcame from your mom

How can Punnett Squares be used to show How can Punnett Squares be used to show how alleles separate when sex cells form how alleles separate when sex cells form

during Meoisis?during Meoisis?

HalfHalf of the sperm of the sperm cells from the cells from the male parent will male parent will receive the receive the chromosomes with chromosomes with the the PP allele; the allele; the other half receive other half receive the the pp allele allele

The same is true The same is true for the egg cells for the egg cells from the from the femalefemale parentparent

If we only have 23 pairs of chromosomes If we only have 23 pairs of chromosomes how do we exhibit so many different traits?how do we exhibit so many different traits?

Each body cell Each body cell contains more contains more than 60,000 than 60,000 genesgenes and each and each of those genes of those genes controls a controls a particular particular traittrait

If you unwrap all If you unwrap all the DNA in your the DNA in your cells you could cells you could reach the reach the moon!!!moon!!!

Section 4: The DNA ConnectionSection 4: The DNA ConnectionWhat is the Genetic Code?What is the Genetic Code?

CellsCells are made up of are made up of chromosomeschromosomes; ; chromosomes are chromosomes are made up of made up of DNADNA; ; DNA is made up of DNA is made up of nitrogennitrogen bases bases

The The orderorder of nitrogen of nitrogen bases along a gene bases along a gene forms a forms a geneticgenetic code code that specifies what that specifies what type of type of proteinprotein will will be producedbe produced

A group of A group of threethree bases codes for the bases codes for the attachment of a attachment of a specific specific aminoamino acid acid

Cell

Chromosome

DNA

Nitrogen bases

What are amino acids?What are amino acids?

The The buildingbuilding blocks of blocks of proteinsproteins

The The orderorder of the of the bases determines bases determines the order in the order in which amino which amino acids are put acids are put together to form together to form a a proteinprotein - like a - like a three-letter three-letter codecode

How do cells make Proteins?How do cells make Proteins?

Protein Protein SynthesisSynthesis – the – the cell uses cell uses information from information from a a genegene on a on a chromosome to chromosome to produce a produce a specific proteinspecific protein

Takes place on Takes place on the the ribosomesribosomes in in the the cytoplasmcytoplasm

What must happen before protein What must happen before protein synthesis can take place?synthesis can take place?

A A ““messengermessenger” ” must first carry must first carry the genetic the genetic code from the code from the DNA inside the DNA inside the nucleus to the nucleus to the cytoplasm – cytoplasm – called called RNARNA

How is RNA different from How is RNA different from DNA?DNA?

DNA looks like a DNA looks like a twisted ladder twisted ladder while RNA while RNA almost always almost always looks like only looks like only oneone strand, or strand, or side, of the side, of the ladder ladder

Instead of Instead of Thymine RNA Thymine RNA contains contains UracilUracil

RNA

What are the types of RNA?What are the types of RNA?

MessengerMessenger RNA RNA – – copiescopies the the coded message coded message from the DNA in from the DNA in the nucleusthe nucleus

TransferTransfer RNA – RNA – carriescarries amino amino acids and adds acids and adds them to growing them to growing proteinsproteins

What is the process of protein What is the process of protein synthesis?synthesis?

A A DNADNA molecule “unzips” between its molecule “unzips” between its base pairs allowing the RNA base pairs allowing the RNA basesbases to to pair up with the DNA bases – Adenine pair up with the DNA bases – Adenine with with UracilUracil

MessengerMessenger RNA leaves the RNA leaves the nucleusnucleus and enters the cytoplasm, where it and enters the cytoplasm, where it attaches it a attaches it a ribosomeribosome and production and production of the protein chain begins (3 letter of the protein chain begins (3 letter code)code)

TransferTransfer RNA attaches to messenger RNA attaches to messenger RNA putting the RNA putting the aminoamino acids it is acids it is carrying in the correct ordercarrying in the correct order

Protein production is complete when Protein production is complete when the ribosome reaches a three-letter the ribosome reaches a three-letter code that acts as a code that acts as a stopstop sign – sign – completed protein chain is releasedcompleted protein chain is released

How do Mutations affect DNA?How do Mutations affect DNA? Mutations can Mutations can

cause a cell to cause a cell to produce an produce an incorrect incorrect proteinprotein during protein during protein synthesissynthesis

Some of the Some of the changes brought changes brought about by mutations about by mutations are are harmfulharmful to an to an organism; however, organism; however, some are helpful or some are helpful or neither harmful or neither harmful or helpfulhelpful