WHY DO WE LOOK THE WAY WE ARE?

WHAT IS GENETICS?Genetics is the scientific study of heredity.

Heredity is the passing of characteristics (traits) from parents to offspring.

Traits vary among individuals.

Traits are determined by genes. Ex.- Your eyes are determined by a specific gene.

Alleles are different forms of one gene.Ex.- An allele for blue eyes and an allele for brown eyes

HOW DO WE KNOW GENES EXIST?GREGOR MENDEL- 1865

Austrian MonkThe father of genetics.Famous study of pea plantsCrossed pea plants with different traits. Ex.- height, seed color, seed shapeObserved that there are factors controlling

each trait.

DEFINITIONSPunnett Squares are diagrams used to

predict genetic crosses. Individuals with identical alleles are called

homozygousIndividuals with different alleles are called

heterozygousPhenotype – physical characteristicGenotype – genetic makeup

HOW TO USE PUNNETT SQUARES Choose a letter to represent the alleles in a

trait. Write the genotypes of the parents. Write one parents alleles above the Punnett

Square, one letter for above each box. Write the other parents alleles on the side on

the Punnett Square, one letter for each box. Fill in the 4 boxes with the possible

combinations. B

B Ex.-Genotypes BB and Bb B b

PUNNETT SQUARETrait for eye color B

BMother has BB genesFather has bb genes b

Uppercase B is dominant lower case b is recessive bHomozygous Brown color= BBHomozygous Blue color = bbHeterozygous =Bb

GENOTYPE =Bb PHENOTYPE= BROWN EYES

Bb Bb

Bb

Bb

DEFINITIONSSexually reproductive- requires 2

organisms that make gametes to produce offspring.

Gamete – A sex cell needed for reproduction.Female gametes- eggsMale gametes- spermSegregate- to move apart or seperate.

MENDEL’S PRINCIPLES• The inheritance of biological characteristics are determined by genes.• For two or more forms of a gene, dominance and recessive forms may exist.• Most sexually reproductive organisms have two sets of genes that separate during gamete formation.• Alleles segregate independently.

Look at the Punnett Square to answer these questions:

How many alleles does each parent have for eye color?

What are they? How many alleles does each parent pass to its

offspring? What are they? B B b

b

Bb Bb

Bb Bb

Look at the Punnett Square to answer these questions:

How many offspring will have blue eyes?What is the percentage of offspring that are

Homozygous for eye color?What is the percentage of offspring that are

heterozygous for eye color? B

B b

b

Bb

Bb

Bb

Bb

Consider this…Alleles are different types of a gene.Genes determine traits.Traits are our genotypes and phenotypes.Genes are located on our chromosomes.Chromosomes contain all of our genetic

information.Parents pass their chromosomes onto their

offspring.Homo sapiens, (Humans), have 46

chromosomes.

HUMANS HAVE 46 CHROMOSOMES

HOW CAN EACH PARENT PASS TRAITS TO THEIR

OFFSPRING?

CAN OFFSPRING HAVE MOM’S 46 + DAD’S 46?

CAN OFFSPRING HAVE 92 CHROMOSOMES?

LAW OF SEGREGATIONHumans have 46 chromosomes.Genes are located on chromosomes.

23 chromosomes come from each parent.22 chromosomes determine traits.1 chromosome determines gender (male or

female).

The Principle of DominanceThe principle of dominance states that some

alleles are dominant and others are recessive.Dominant alleles are always expressed.Recessive alleles are only expressed if both

alleles are recessive.

Dominant means to be expressed.Recessive means to be hidden.

Beyond Dominant and Recessive

Dominant and Recessive traits are not the only way to produce a phenotype.

Other ways phenotypes are produced are through:

Incomplete DominanceCodominanceMultiple AllelesPolygenetic traits

What do you think incomplete dominance means?

HINT:

Incomplete Dominance – One allele is not completely dominant over the other. Ex.-White flower crosses with a red = pink flower.

What do you think codominance means?

HINT:

Codominance – Both alleles contribute to the phenotype.

Ex.-Red cow X White Cow = Roan Cow.

What does multiple alleles suggest when considering a phenotype?

HINT:

Multiple Alleles – More than two alleles control the phenotype.

Ex.- Coat color of rabbits.

What do you think polygenic traits means?

HINT:

Polygenic traits – Several genes control the trait. Ex.-Skin color in humans.

ACTIVITY: STUDY THE CHART AND LIST ONLY THE EXPRESSED TRAITS FOR YOURSELF.

TRAIT DOMINANT

RECESSIVE

SHAPE OF FACE

OVAL [O] SQUARE [o]

EARLOBES

FREE [F] ATTACHED [f]

DIMPLES DIMPLES [D] NONE [d]

BROW SIZE

BROAD [W] SLENDER [w]

EYE COLOR

BROWN [B] HAZEL {h}GREEN [g] BLUE [u]

HAIR COLOR

DARK [K]NON-RED

BLONDE [e]LT [t] RED [r]

TRAIT YOU

MOM

DAD

SHAPE OF FACE

O o O

EARLOBES

F F f

DIMPLES D D DBROW SIZE

w w w

EYE COLOR

h h B

HAIR COLOR

t t K

HAIR TYPE V V V

FAMILY CHARACTERISTS

CURLY= HOMOZYGOUS [C]STRAIGHT=HOMOZYGOUS [S]WAVY=HETEROZYGOUS [V]

HAIR TYPE

HOMEWORKTake out your Family Trait Chart.Use a pencil for this activity.Complete the Punnett Square worksheet.Create a Punnett Square for each trait.From your data determine your parents

second allele for that trait. Their geneotype.Be prepared to discuss your results and any

problems you encountered.