Monohybrid CrossesObjective1.Use the punnett square method to determine the possible genotypes of different monohybrid crosses2.Determine the phenotypic ratio of a monohybred cross.3.Explain how the process of meiosis and fertilization account for the transmission of inherited characteristics.

The transfer of characteristics (traits) from one generation to another

Your inherited characteristics (traits) are determined by the genes located on your chromosomes

Inheritance - Mendel

Dominant Trait

Description

# of students with Dominant

# of students with Recessive Ratio of

Dominant to

Recessive

Percentage with

Recessive traitsClass Class

Eye colour

Hair colour

Hairline

Freckles

Earlobe

Fingers

Ear rim

Thumb joint

Folded hands

Tongue rolling

Chin dimple

a short segment of a chromosome coding for one trait

Gene

chromosomes are found in pairs in humans, there are 46 chromosomes,

made up of 23 pairs of homologous chromosomes

a pair of chromosomes consists of two homologous chromosomes which look alike and carry genes for the same traits

you receive one homologous chromosome of the pair from each parent, therefore you receive 2 genes for each trait

Homologous chromosomes:

This term is used to describe the physical or visible appearance of an individual as determined by the gene combination you inherit from your parents.

Example: in the case of eye colour, having brown eyes is the phenotype and is dominant

Phenotype

the gene combination that produces the trait

these genes may be the same or different

genotypes are represented by upper and/or lower case letters e.g. Bb

there are three possibilities for genotypes for a single trait.

e.g. BB or Bb or bb

Genotype

alternate forms of a gene same location on a each chromosome of

pair affects the same trait but differently alleles are different forms of a gene that

carry different instructions eg. Brown eyes or blue eyes

Allele

Characteristic that is always expressed its gene is present

only one dominant allele needs to be present for the dominant trait to be expressed

an upper case letter designates a dominant allele

  eg. Tall is dominant. It is represented with

a “T”

Dominant Trait/Allele

Characteristic that is only expressed when two genes for that trait are present

two recessive alleles need to be present for a recessive trait to be expressed

if a dominant allele is present it “masks” the recessive allele

eg: Short is recessive. It is represented with a

“t”

Recessive Trait/Allele

“homo” means the “same” the condition where both alleles for a trait

are the same there are two conditions for homozygous

genotype: homozygous recessive genotype “aa” homozygous dominant genotype “AA”

Homozygous Genotype

“hetero” means “different” the condition where both alleles for a trait

are different the genetic information inherited for a trait

from both parents is different example: heterozygous genotype “Aa”

Heterozygous Genotype

Summary (example eye colour)

Genotype Condition PhenotypeBB Homozygous

dominantBrown eyes

Bb Heterozygous Brown eyesbb Homozygous

recessiveBlue eyes

Crossed two purebred parents (One tall -T and one short -t) Pure breeding plants always produce

identical offspring. All offspring were tall!!

Mendel concluded that some traits were ___________ and some traits were ___________.

Mendel’s Experiment

When individuals with different traits are crossed, the offspring (F1 generation) will express only the dominant trait.

Parents: Tall x ShortF1 (Offspring): Tall Tall Tall Tall

What must the genotype of the offspring be if the parents were pure breeding?

Principal of dominance

Mendel crossed the F1 generation. He crosses two hybrid pea plants.

Hybrids have contrasting traits.

F1: Tall plants x Tall plants F2 (Offspring of F1): Tall Tall Tall

Short F2 generation = 3:1 ratio

What must the genotype of these offspring be if the parents were hybrids (Tt and Tt)?

What happened next??

Each F1 parent starts with two hereditary factors (alleles); one is dominant and one is recessive

Each parent contributes only one factor (allele) Each offspring inherits one factor (allele) from

each parent If the dominant factor (allele) is present it will

be expressed. If the recessive factor (allele) is present it will

only be expressed if only recessive factors are present.

Law of Segregation

Mendel crossed two purebred plants TT – tall plant Tt – short plant

Monohybrid cross – only one trait is being tested

Monohybrid Cross

Punnett Square Is a grid system resembling a checkerboard,

used in computing possible results of various genetic combinations

Simply stated, it is a way of representing the possible combinations of genes when an egg and sperm unite in fertilization

Punnett Squares

 Characteristic hair texture – ◦ Dominant allele (gene) is curly hair - C. ◦ Recessive allele (gene) is straight hair - c

Mother ◦ Phenotype – straight hair◦ Genotype- homozygous recessive - cc

Father ◦ Phenotype – curly hair ◦ Genotype – homozygous dominant – CC

Predicting genotype and phenotype possibilities using Punnett Squares

Egg

Spermc c

C Cc Cc

C Cc Cc

Punnett SquareAll of their children will have curly hair. They all have a different genotype from their parents.

Fig. 18.5

Fig. 18.6

Fig. 18.13

Fig. 18.14

Your Turn Bikini Bottom Genetics – Monohybrid

Crosses

HOMEWORK: Find out what the following words mean…

Hybrid Pure-breeding/Purebred Why was it important that Mendel used

purebred plants in his experiment? How does meiosis ensure that you inherit

your mothers and fathers characteristics?

Codominance, Incomplete dominance and Dihybrid Crosses

Objectives:1. Explain what co dominance and

incomplete dominance is. Give an example of each.

2. Use a Punnett square to solve basic incomplete and co dominance crosses

3. Use a Punnett square to solve basic dihybrid crosses.

Terms Incomplete Dominance: When two alleles

are equally dominant, they interact to produce a new phenotype.

Codominance: When both alleles are dominant and are expressed at the same time.

Pg 145 # 1-4

Codominance

When a red bull iscrossed with a white cow, the offspring willbe roan.

Incomplete DominanceWhen a red flower is crossedwith a red flower,the resulting offspringwill be pink.

Dihybrid Crosses A type of cross that involves two genes,

each consisting of non identical alleles.

RY RYryry

What happened when Mendel crossed two pea plants that different in TWO traits?

In his second experiment Mendel crossed a pea plant with round/yellow (RRYY) seeds with a pea plant with wrinkled/greed seed (rryy).

What genotypes resulted?

What phenotypes resulted?

RY RYry RrYy RrYyry RrYy RrYy

Genotype: RrYy F1 - GenerationRatio 100%Phenotype: Round/YellowRatio 100%

RY Ry rY ryRYRyrYry

Crossing F1(RrYy) x F1(RrYy)

RY Ry rY ryRY RRYY RRYy RrYY RrYyRy RRYy RRyy RrYy RryyrY RrYY RrYy rrYY rrYyry RrYy Rryy rrYy rryy

What genotypes resulted?

What phenotypes resulted?

Genotype: RRYY RRYy Rryy RrYY RrYy rrYY rrYyrryy

Ratio: 1 2 2 2 4 1 2 1Phenotype: Round/Yellow Round/Green Wrinkled/Yellow Wrinkled/GreenRatio: 9 3 3 1

In the resulting F2 – Generation, the phenotypic ratio will always be 9:3:3:1In other words, the likelihood of obtaining each of the above phenotypes from crossing two hybrid pea plants is 9:3:3:1.

The inheritance of alleles for one trait ________ (does/does not) affect the inheritance of alleles for another trait.

Law of Independent Assortment

Plenary Bikini Bottom

Questions