Genetics and Heredity

GENETICSGENETICS Study of the Study of the

passing on of passing on of characteristiccharacteristics from one s from one organism to organism to its offspringits offspring

HEREDITYHEREDITYThe passing of The passing of traitstraits from parents to from parents to offspring.offspring.

TRAITTRAIT A A characteristic characteristic of an of an

organismorganism Examples include: height, skin Examples include: height, skin

color, eye color, freckles, nose color, eye color, freckles, nose shape, etc.shape, etc.

Traits are controlled by Traits are controlled by genesgenes..

GENEGENE• The set of information that a The set of information that a controlscontrols a trait a trait• It is a segment of It is a segment of DNADNA on a on a chromosomechromosome Genes come in 2Genes come in 2 forms (forms (alleleallele-forms of a -forms of a

gene):gene): a. a. DOMINANTDOMINANT: allele that will always be : allele that will always be

expressed (shown) in an offspringexpressed (shown) in an offspring• Tries to Tries to PREVENTPREVENT the expression of the expression of recessive generecessive gene

b. b. RECESSIVERECESSIVE: allele that will only : allele that will only be expressed if there are no be expressed if there are no dominant alleles presentdominant alleles present

• Is Is preventedprevented from showing up if from showing up if there is a dominant allele presentthere is a dominant allele present

Example: Example: Eyecolor- Brown eyes are Eyecolor- Brown eyes are dominantdominant and and

blue eyes are blue eyes are recessiverecessive.. A person can have a brown allele and a A person can have a brown allele and a

blue allele but still have brown eyes blue allele but still have brown eyes because the brown allele is dominant and because the brown allele is dominant and hides the blue allele (it’s recessive).hides the blue allele (it’s recessive).

Dominant alleles are represented with a Dominant alleles are represented with a capitalcapital letter.letter.

Recessive alleles are represented with a Recessive alleles are represented with a lowercaselowercase letter. letter.

R = DominantR = Dominant r = recessiver = recessive An organism is represented by An organism is represented by twotwo letters for letters for

each allele (or gene that comes from mom and each allele (or gene that comes from mom and dad)dad)

Homozygous Homozygous (purebred)-when a species (purebred)-when a species has two identical (genes)alleles for a traithas two identical (genes)alleles for a trait

Represented by the same 2 lettersRepresented by the same 2 letters Ex. BB (dominant) or bb (recessive)Ex. BB (dominant) or bb (recessive) HeterozygousHeterozygous (hybrid)-when a species (hybrid)-when a species

has two different (genes) alleles for a traithas two different (genes) alleles for a trait Represented by 2 different lettersRepresented by 2 different letters Ex. Bb Ex. Bb

GenotypeGenotype- genes in an organism that are - genes in an organism that are presentpresent

Ex. Bb, bb or BBEx. Bb, bb or BB PhenotypePhenotype- an organism’s physical traits - an organism’s physical traits

(or visible traits)(or visible traits) Ex. Brown eyes, brown hairEx. Brown eyes, brown hair

MUTATIONMUTATION Change in a Change in a

gene’s gene’s information information (like a (like a change in change in instructions)instructions)

Mutations can be:Mutations can be: HELPFULHELPFUL HARMFUL HARMFUL Examples Examples

include: include: Down’s Down’s syndrome, color syndrome, color blindness, blindness, albinism, sickle albinism, sickle cell anemiacell anemia

NEUTRALNEUTRAL

PUNNET SQUAREPUNNET SQUARE A mathematical A mathematical

model used to model used to predict the predict the chances that chances that offspring will offspring will inherit genes inherit genes from their from their parentsparents

SAMPLE PUNNET SQUARE

Practice problem #1Practice problem #1 Predict the genotypes for the fur color of Predict the genotypes for the fur color of

the offspring of a brown, heterozygous the offspring of a brown, heterozygous hamster and a white homozygous hamster and a white homozygous hamster. Brown is dominant and white is hamster. Brown is dominant and white is recessive.recessive.

Use any letter you like. Use any letter you like.

Problem #2Problem #2 Predict the gentoypes of the offspring of Predict the gentoypes of the offspring of

2 white homozygous cows. Black is 2 white homozygous cows. Black is dominant over white. dominant over white.

Use any letter you like.Use any letter you like.

#2#2

Problem #3Problem #3 Predict the genotypes of the offspring of Predict the genotypes of the offspring of

2 gray heterozygous rats. Gray is 2 gray heterozygous rats. Gray is dominant over white, which is recessive.dominant over white, which is recessive.

Use any letter you like.Use any letter you like.

#3#3

Practice problem #4Practice problem #4 What are the chances of having a girl or What are the chances of having a girl or

a boy baby?a boy baby?

How would you make a punnett square to How would you make a punnett square to show it?show it?

#4#4

Pedigree ChartsPedigree Charts Pedigree: a Pedigree: a chartchart of the genetic history of the genetic history

of a family over several generationsof a family over several generations They are used to find out the They are used to find out the probability probability

of a child having a disorder or a certain of a child having a disorder or a certain trait in a family.trait in a family.

Symbols on a PedigreeSymbols on a Pedigree

Female:

Male:

Connecting Pedigree Connecting Pedigree Symbols:Symbols:

Examples of connected symbols:Examples of connected symbols: Married couple Married couple

Children Children

More symbols in a Ped. More symbols in a Ped. Chart: Chart:

Example of a ped. Chart:Example of a ped. Chart: What does a pedigree chart look like?What does a pedigree chart look like?

Interpreting a Ped. Chart:Interpreting a Ped. Chart: 1. Determine if the pedigree chart shows 1. Determine if the pedigree chart shows

an autosomal or X-linked an autosomal or X-linked disease/disorder.disease/disorder.

If one sex in the pedigree is affected, it is If one sex in the pedigree is affected, it is X-linked.X-linked.

It is a 50/50 ration between sexes, the the It is a 50/50 ration between sexes, the the disorder/disease is disorder/disease is autosomal.autosomal. Autosomal doesn’t affect just one sex.Autosomal doesn’t affect just one sex.

Is it autosomal or X-Is it autosomal or X-linked?linked?

Autosomal…why????Autosomal…why????

Interpreting Ped. Chart Interpreting Ped. Chart cont.cont.

2. Determine whether the disorder is 2. Determine whether the disorder is dominant or recessive.dominant or recessive.

If it is dominant, If it is dominant, one one of the parents must of the parents must have the disorder/trait/disease.have the disorder/trait/disease.

It is is It is is recessiverecessive, neither parent has to , neither parent has to have the trait/disorder because they can have the trait/disorder because they can be heterozygous (Bb).be heterozygous (Bb).

Dominant or Recessive?Dominant or Recessive?

Dominant….why????Dominant….why????

Dominant or Dominant or Recessive???Recessive???

Recessive…..why???Recessive…..why???

You are researching the inheritance of a red You are researching the inheritance of a red colored tongue in a lizard….colored tongue in a lizard….

Is it autosomal or X-linked?Is it autosomal or X-linked? Is it dominant or recessive?Is it dominant or recessive?