CHARACTERISTICS OF LIFE

All Living Things reproduce!!!

All Living Things Have DNA!!!

WHY ARE WE ALL DIFFERENT?

We all inherited different genes from our parents which determines our traits.

Heredity – Passing on of genes which determine your traits from parentsto offspring.

23 chromosomes from each parent.

Genes – Pieces of DNA that carry hereditaryinstructions and are passed from parents.

Traits – A distinguishing characteristic that is passed from parents to offspring.

Genetics – Study of heredity (passingon of genes)

Johann Gregor Mendel was born July 22, 1822. Mendel became a friar at the Augustinian monastery in Brno, Czechoslovakia. From 1868 until his death, Mendel was the abbot of the monastery.

Mendel was experimenting with flowers in the monastery's gardens. He wondered how traits were passed from parent to offspring. He studied the relations between parents and offspring with mathematical symbols. His favorite plants to experiment with were peas.

FATHER Of genetics

MENDEL’S EXPERIMENT

PART 1He bred a tall pea plant with a pure short pea plant. But ALL the offspring were TALL. How could that be?Maybe a mistake was made?PART 2He crossed 2 of the offspring from the abovecross.Results – 75% Tall

25% ShortNow wait a minute!! He crossed two tall and go a short? What’s going on?????

GENETIC RULES

Every organism has TWO forms of a gene for each trait. One from each parent. Each form is called an ALLELE.

You can receive a dominant or recessive gene from your parent.

GREGOR MENDELHe realized in the first cross, onetrait appeared and the other seemed to be masked. * The trait that masks or is stronger than the other trait is called the dominant trait. * The trait that is covered up is called the recessive trait.

For these reasons, Mendel is called the Father of Genetics.

GENETICS RULES and SYMBOLS

Capital Letters – Represents dominanttrait. Dominant traits are the stronger traits.Lower Case Letters – Represents recessive trait. Recessive traits are the weaker traits that are often masked by dominant traits.

Scientists use symbols to represent different forms of a gene.

Examples-BB – brown eyes bb - blue Bb – brown eyes

Example Dominant TraitsBrown Eyes- BWidow’s Peak- WUnattached Earlobes- EFreckles- F

Example Recessive Traits

Blue eyes- bStraight hairline- wAttached earlobes- eNo Freckles- f

If the inherited genes (alleles) are the same, then they are called HOMOZYGOUS or purebred. Letters are the same size.Examples – aa , AA , LL , ll , TT , tt

If the inherited genes are different, then they are called HETEROZYGOUS or hybrid. Letters are different sizes.Examples – Aa , Ll , Tt, Bb

Homozygous vs. Heterzygous

The genotype is the letter combination or gene combinations

Example – Tt, Aa, bb,or Ll

The phenotype is the actual appearance ofthe organism.

Example – tall, brown hair, blue eyes, longtoes

Genotype vs. Phenotype

GENETIC PROBABILITY

Mendal crossed yellow and green pea plantsand discovered that 1 out of 4 were green.

He was using probability.

Probability – The possibility or likelihood thata particular event will occur.

Used to predict the results of geneticscrosses.

PUNNETT SQUARESA Punnett square is a special chart used to show the possible gene combinations in a cross between 2 organisms. (also called monohybrid crosses)

Developed by an English geneticist by the name of Reginald

Punnett.

PARTS OF A PUNNETT SQUARE

Male Genes

FemaleGenes

Offspring Combinations

T= tongue rollt= cannot roll tongue

How does a Punnett Square Work?• Draw a square and divide

it into 4 sections. • Write the gene pairs

across the top of the box, then the

other down the side. • In each box, place the

correct gene to see the possible combinations.

Each square represents a 25%possibility of getting that trait.

Tt Tt

Tt Tt

Cross betweenhomozygous dominant curly tail (TT) and a homozygousrecessive straight tail (tt).

What are the percentages of the offspring?What are the genotypes?What are the phenotypes?

Tt Tt

Tt Tt

Cross betweentwo heterozygous curly tailed parents (Tt).

What are the percentages of offspring?What are the genotypes?What are the phenotypes?

TT Tt

Tt tt

Mathematical Computations

In a Punnett Square where both parents are

hybrids the percents are listed below:

25% purebred (homozygous) curly – TT 50% hybrid (heterozygous) curly - Tt

25% purebred (homozygous) straight - tt

% of same genotype as parents - 50 %

% of same phenotype as parents -

75%

Dihybrid Crosses

Mom T t

S

s

Dad T t

S

s

A dihybrid cross is a cross of two different traits

T- height S-shape

T-tall t-shortS-square s-round

List of gamete genotypes:Mom-Dad-

Dihybrid crosses- formation of zygote

Formation of zygote

ST(sperm)

St(sperm)

sT(sperm)

st(sperm)

ST (egg)

St(egg)

sT(egg)

st(egg)

Mom- ST, St, sT, stDad- ST, St, sT, st

When parent gametes (egg/sperm) join to form a zygote, the possible offspring gene combinations are as follows:

Dihybrid Crosses

Parent generation = gene pairs given by parents.

Gametes = half of parent gene pair

1st Generation= combination of gametes to produce offspring.

2nd Generation= possible combination of offspring from 1st generation cross The possible gene

combinations from 1st generation offspring

Practice

G-eye sizeG-large

g-small

B- eyebrowsB-separated

b-attached

The squares contain the gene combinationsthat could occur in the cross.

The genotype is the letter combination or gene combinations in the squares.

Example – Tt, Aa, bb,or Ll

The phenotype is the actual appearance ofthe organism.

Example – tall, brown hair, blue eyes, longtoes

INCOMPLETE DOMINANCESometimes, you may notice that traits can blend together. Two capital letters are used.For example: Red & White are equally dominant producing Pink flowers.

Examples – roan color in horses and cows, pink color in flowers are red and white combined.

Codominance

When both alleles contribute to the phenotype.

For example: Chickens- black & white feathers are codominant, therefore they can appear speckled.