Mendel’s Principle of Dominance or Recessiveness

Traits found in humans

Modified by Mrs. Snyder

January 2015

What is the relationship between DNA and your physical appearance?

Take a moment to think about what you know about DNA, chromosomes, and ribosomes. Write down several ideas.

Now, look at the image to the right.

What are genes? See page 111

What are genes?

If genes control traits, then we need to find out how they do this. Two alleles exist for each gene (because

chromosomes are paired.) (page 111) For now we will keep things simple. The presence or absence of an allele impacts

an organism’s appearance. The terms dominant, recessive,

homozygous, and heterozygous are important for you to understand.

Terms defined Dominant – page 109 Recessive – page 109 Homozygous vs

heterozygous How are alleles

represented? Probability: pages

111- 113

Explore 1 Fundamentally Genetics

You and your groups will be looking at each other to determine whether you are dominant or recessive for the following traits.

More terms Genotype phenotype

Tongue Rolling

Earlobes

Earbump Often called Darwin’s Ear Bump Dominant - Having a small bump on the

ear Recessive - Not having the bump

Widow’s Peak

Hitchhiker’s Thumb

Cleft Chin

Clockwise Hair Whorl

Here is the link to the lab we are going to do Obtain a lap top when directed. Create an excel chart It should have 8 columns Label as directed

Period 3 Lab: Partners – randomly generated John, Rebecca Laura, Ilana Tae, Jessie Alex, Gino Kylie, Maria

Grace, Justin Andrew, Robert Nia, Gianna DJ, Cooper

You are a team of scientists. You are studying the random distribution of traits (this occurs during meiosis) and will use your traits as an example. One person is the “mother” and one is the father.

Period 7 Partners – randomly generated

You are a team of scientists. You are studying the random distribution of traits (this occurs during meiosis) and will use your traits as an example. One person is the “mother” and one is the father.

Period 8 Partners – randomly generated

You are a team of scientists. You are studying the random distribution of traits (this occurs during meiosis) and will use your traits as an example. One person is the “mother” and one is the father.

Explore 2 Punnett Squares

You will be able to predict the outcomes of crosses by completing this next activity.

Mendel & The Gene Idea

Explain

Mendel and Genetics Answer the following questions as we

explain the concepts surrounding basic genetic

It All Began with Mendel (FYI) Gregor Mendel was born in 1822. Called the “Father of Genetics” Late 1800 chromosomes and the process of

meiosis were unknown. Mendel’s work was considered obscure and

unimportant until 1900 Walter Sutton proposed the Chromosome

Theory and people began to listen to his ideas. Chromosome Theory – specific genes are

located on specific chromosomes

Three Conclusions to His Research1. Principle of Dominance and

RecessivenessOne allele in a pair may mask the effect of

the other

2. Principle of SegregationThe two alleles for a characteristic separate

during the formation of eggs and sperm

3. Principle of Independent AssortmentThe alleles for different characteristics are

distributed to reproductive cells independently.

Mendelian genetics Character

(heritable feature, i.e., fur color) Trait (variant

for a character, i.e., brown) True-bred

(all offspring of same variety) Hybridization

(crossing of 2 different true-breds) P generation (parents) F1 generation (first filial generation)

Genetic vocabulary……. Punnett square: Gene: point on a chromosome

that controls the trait Allele: an alternate form of a gene

A or a Homozygous: identical alleles

for a character Heterozygous: different alleles

for a gene Phenotype: physical traits Genotype: genetic makeup Testcross: breeding of a

recessive homozygote X dominate phenotype (but unknown genotype)

How can the Chances of an Offspring’s Traits be Determined? BY USING A PUNNETT SQUARE Get out your Punnett Squares Problems In groups of two come to the board and

complete the given monohybrid problems.

Bb X BbPhenotypic Ratio

3:1Genotypic Ratio

1:2:1 B b

B

b

B B B b

b B b b

Exploration 4 What about two traits? Complete the second half of your Punnett

Square Problems

What about 2 Traits? BbTt x BbTt The Gametes contain one

of each of the alleles. (BT).

Each of the offspring contain four alleles exactly like the parents.(BbTt).

Notice the number of possible offspring has increased.

The phenotypic ratio is 9:3:3:1

BbTt x BbTtBT Bt bT bt

BT BBTT BBTt BbTT BbTt

Bt BBTt BBtt BbTt Bbtt

bT BbTT BbTt bbTT bbTt

bt BbTt Bbtt bbTt bbtt

Exceptions to Mendel’s Rule

Incomplete Dominance The phenotype of the

heterozygote is intermediate between those of the two homozygotes.

Ex) Snap Dragon Color

Red, Pink, White

Co-dominance Phenotype of both

homozygotes are produced in heterozygotes individuals.

Both alleles are expressed equally.

Ex)Roan Cattle White-feathered birds are both homozygotes for both B and W alleles

Multiple Alleles

Ex )Blood type Blood type A and B are co-dominant,

while O is recessive. Forms possible blood types of A, B, AB,

and O.

Blood Also Shows Codominance

Sex-Determination Chromosome pairs 1-22 are autosomes Chromosome pair 23 are sex chromosomes They determine the sex of an individual XX = female XY = male

Sex-Linked Inheritance Traits that are only found on the X

chromosome Colorblindness and Hemophilia are

examples of sex-linked traits. These genes are recessive and found only

on the X chromosome.

Polygenic Inheritance Inheritance pattern of a

trait that is controlled by two or more genes.

Gene may be on the same chromosome or on different chromosomes.

Ex) Skin color and Height

ELABORATION 1Exceptions to the Rule

Punnet Squares: Dihybrid, Sex-Linked, Multiple Alleles, Co-Dominance, Incomplete Dominance

Elaboration 2 Who’s the Parents?

Upon completion of this lab, you will: determine the ABO blood types of two sets of

parents and two newborn children examine the genetic relationships possible

between the parents and children match the “mixed up” children with their proper

parents.