HeredityHeredity

Heredity is the passing of Heredity is the passing of traits from one generation to traits from one generation to another, or inheritance.another, or inheritance.

Inherited Traits vs. Inherited Traits vs. Environmental FactorsEnvironmental Factors

• Inherited Traits are those that are Inherited Traits are those that are passed from parent to offspringpassed from parent to offspring

• Environmental Factors can also have an Environmental Factors can also have an effect on how you lookeffect on how you look– DietDiet– ExerciseExercise– Smoking/DrinkingSmoking/Drinking– Sun exposure Sun exposure

Why do I look like my parents?!Why do I look like my parents?!

You look like your parents because You look like your parents because genetic information (DNA) is passed from genetic information (DNA) is passed from parent to offspring during sexual parent to offspring during sexual reproduction.reproduction.Each sex cell (egg or sperm) of the parent Each sex cell (egg or sperm) of the parent organism (plant or animal) contains one-organism (plant or animal) contains one-half of the genetic material needed to half of the genetic material needed to create a new organism.create a new organism.

Who do you look like?Who do you look like?

Draw a picture of yourself and then label Draw a picture of yourself and then label all of the traits that you inherited from all of the traits that you inherited from someone in your family (write the family someone in your family (write the family member’s name beside that trait)member’s name beside that trait)

For example, if your hair is red and your For example, if your hair is red and your mother’s hair is red, write her name mother’s hair is red, write her name beside your hair.beside your hair.

What are Chromosomes?What are Chromosomes?

A structure found in the nucleus of a A structure found in the nucleus of a cell that contains the genetic cell that contains the genetic information (DNA).information (DNA).

Remember, these are those things you were Remember, these are those things you were drawing that doubled and split in Mitosis and drawing that doubled and split in Mitosis and Meiosis. Humans have 46 in every cell except Meiosis. Humans have 46 in every cell except sex cells, which have 23. sex cells, which have 23.

What Is a Gene?What Is a Gene?

• A gene is a segment of A gene is a segment of DNA found on a DNA found on a chromosome that chromosome that determines the determines the inheritance of a inheritance of a particular trait.particular trait.

• Genes are what make Genes are what make one individual look one individual look different from anotherdifferent from another

Principles of HeredityPrinciples of Heredity

1.1. Each trait is governed by two Each trait is governed by two factors – now called genes.factors – now called genes.

2. Genes are found in alternative 2. Genes are found in alternative forms called alleles. forms called alleles.

3. Some alleles are dominant and 3. Some alleles are dominant and mask alleles that are recessive. mask alleles that are recessive.

Dominant TraitsDominant Traits

Dominant Trait- a trait that will always be Dominant Trait- a trait that will always be expressed in the phenotype.expressed in the phenotype.These alleles are represented by a capital These alleles are represented by a capital letter.letter.

Ex. Having a widow’s peak is dominant to Ex. Having a widow’s peak is dominant to not having a widow’s peak. not having a widow’s peak.

Recessive TraitRecessive Trait

Recessive Trait- a trait that will only be Recessive Trait- a trait that will only be expressed in the phenotype if two expressed in the phenotype if two recessive alleles are present. In the recessive alleles are present. In the presence of a dominate trait, the presence of a dominate trait, the recessive trait will not be expressed. recessive trait will not be expressed. These alleles are represented by These alleles are represented by lowercase letters.lowercase letters.

Ex. Hitchhiker’s thumb is recessive to straight Ex. Hitchhiker’s thumb is recessive to straight thumb.thumb.

Seven Traits used by Mendel in Genetic StudiesSeven Traits used by Mendel in Genetic Studies

Genotype and PhenotypeGenotype and Phenotype

Genotype: alleles carried by an Genotype: alleles carried by an individual ex. RR, Rr, rrindividual ex. RR, Rr, rr

Phenotype: physical characteristic Phenotype: physical characteristic or appearance of an individual or appearance of an individual ex. Round, wrinkledex. Round, wrinkled

Principles of HeredityPrinciples of Heredity

HomozygousHomozygousDominantDominant

HomozygousHomozygousRecessiveRecessive

HeterozygousHeterozygous

Mendel’s Experiment with PeasMendel’s Experiment with Peas

Round seed x Wrinkled seed Round seed x Wrinkled seed RR rrRR rr

F1: All round seed coatsF1: All round seed coats RrRr

R R R R

Homozygous parents can only pass one Homozygous parents can only pass one form of an allele to their offspring. form of an allele to their offspring.

R r R r

Heterozygous parents can pass either Heterozygous parents can pass either of two forms of an allele to their offspring. of two forms of an allele to their offspring.

Principles of HeredityPrinciples of Heredity

Mendel was a scientist studying peas as a Mendel was a scientist studying peas as a way to explore genetics. way to explore genetics. He needed to explain:He needed to explain:

1.1. Why one trait seemed to disappear in Why one trait seemed to disappear in the first generation.the first generation.

2. Why the same trait reappeared in the 2. Why the same trait reappeared in the second generation in one-fourth of the second generation in one-fourth of the offspring. offspring.

Mendel’s Principle of Genetic Mendel’s Principle of Genetic

SegregationSegregation

In the formation of gametes, the In the formation of gametes, the members of a members of a pair of alleles separatepair of alleles separate (or segregate) cleanly (or segregate) cleanly from each other so that only one member is from each other so that only one member is included in each gamete.included in each gamete.

Each gamete has an equal probability of Each gamete has an equal probability of containing either member of the allele pair.containing either member of the allele pair.

Genetic Segregation Genetic Segregation

Parentals: Parentals: RR x rrRR x rr

R R r r R R r r

RR

RR

r r r r

F1 x F1: F1 x F1: Rr x RrRr x Rr

R r R r R r R r

½ R½ R

½ r½ r

½ R ½ r ½ R ½ r ¼ RR¼ RR ¼ Rr¼ Rr

¼ Rr¼ Rr ¼ rr¼ rr

RrRr RrRr

RrRr RrRr

Genetic Segregation Genetic Segregation

Genotypic Ratio: ¼ RR + ½ Rr + ¼ rrGenotypic Ratio: ¼ RR + ½ Rr + ¼ rr

Phenotypic Ratio: ¾ Round + ¼ WrinkledPhenotypic Ratio: ¾ Round + ¼ Wrinkled

Mendel’s Principle of Mendel’s Principle of Independent Assortment Independent Assortment

When gametes are formed, the When gametes are formed, the alleles of one gene segregate alleles of one gene segregate independently of the alleles of independently of the alleles of another geneanother gene producing equal producing equal proportions of all possible gamete proportions of all possible gamete types. types.

Using Probability in Genetic Using Probability in Genetic AnalysisAnalysis

1. Probability (P) of an event (E) occurring:1. Probability (P) of an event (E) occurring:

P(E) = P(E) = Number of ways that event E can occurNumber of ways that event E can occur

Total number of possible outcomesTotal number of possible outcomes

Eg. P(Rr) from cross Rr x RrEg. P(Rr) from cross Rr x Rr 2 ways to get Rr genotype 2 ways to get Rr genotype 4 possible outcomes 4 possible outcomes P(Rr) = 2/4 = 1/2 P(Rr) = 2/4 = 1/2

Sex Determination Sex Determination

Female Male Female Male XX x XYXX x XY

½ X½ X

½ Y½ Y

½ X ½ X½ X ½ X

¼ XX¼ XX ¼ XX¼ XX

¼ XY¼ XY ¼ XY¼ XY

Phenotypic Ratio of OffspringPhenotypic Ratio of Offspring ½ Female + ½ Male½ Female + ½ Male

Colorblindness Colorblindness

Pedigree for Colorblindness, Pedigree for Colorblindness, an X-linked Recessive Traitan X-linked Recessive Trait