Mendel’s Principle of Dominance or Recessiveness

Traits found in humans

Engage Map of X and Y Chromosomes

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.

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

Polydactyly

Syndactyly Feet

Syndactyly Hands

Severe Syndactyly

Syndactyly Surgery

Cleft Chin

Clockwise Hair Whorl

Autosomal Dominant and Recessive Huntington Disease – Dominant Disease Cystic Fibrosis – Recessive Disease

Sickle Cell Anemia

Tay-Sach’s

PKU

Explore 2 Bugs, Bugs, Bugs

Genes for traits are encoded and arranged linearly on structures called chromosomes found in the nuclei of most cells. When organisms reproduce, the resulting offspring should receive an equal number of chromosomes from the mother and the father.

In this activity you use the chromosomes and Bug Traits Key to determine the genotype and phenotype of the offspring.

Exploration 3 Wisconsin Fast Plant Genetics Lab

Explore 4 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.