1.Tell me all of the possible gamete combinations for a parent with this genotype for two traits:

Bb Tt

2. Match the following vocab words with their definitions:

Diploid A. A genotype combination in which there is a dominant and recessive allele

Haploid B. The allele combination for a specific trait.

Genotype C. A cell with two of each kind of chromosome (body cell)

Phenotype D. A genotype combination in which the alleles for the trait are the same.

Heterozygous E. The physical characteristic that you see, due to someone’s inheritance.

Homozygous F. A cell containing one of each type of chromosome (gamete)

MAKE SURE YOUR NOTEBOOK GOES IN THE CABINET BEFORE YOU LEAVE TODAY- I AM GRADING

• Patterns of inheritance that are explained by Mendel’s experiments are often referred to as “simple genetics”.

• However, many inheritance patterns are more complex than those studied by Mendel.

COMPLEX PATTERNS OF INHERITANCE

• For example:

A homozygous red-flowered plant (RR) is crossed with….

a homozygous NO PIGMENT-flowered plant (R′ R′), also dominant

all of the first generation offspring will have pink flowers- they are only showing half of the red pigment.

INCOMPLETE DOMINANCE Only displaying half of one allele

R R R’ R’

R R’

Law of Segregation?

R R’½ Red ½ No Pigment

In co-dominance, both alleles are DOMINANT and expressed equally.

CO-DOMINANCE An expression of both alleles

Black-colored feathers

F F

White-colored feathers

F FB B W W

F FB W

Co-dominance in Humans

One example of this in humans is a type of sickle-cell disease.

• Sickle-cell diseases cause the red blood cells to be deformed.

• In an individual who is homozygous for the sickle-cell allele, the oxygen-carrying protein hemoglobin differs

by one amino acid from normal hemoglobin.

Hb HbS S

Co-dominance in Humans

• Individuals who are heterozygous for the allele produce both normal and sickled hemoglobin, an

example of codominance.

Hb HbA S

• Individuals homozygous for the normal hemoglobin allele have this genotype :

Hb HbA A

• Although each trait has only two alleles in the patterns of heredity you have studied thus far, it is common for more than two alleles to control a trait in a population.

Traits controlled by more than two alleles have multiple alleles.

An example is Blood Type.

MULTIPLE ALLELES More than two alleles in a population

Human Blood Types

lA lA or lAilB lB or lBi

lA lB

ii

Genotypes Phenotypes

AB

ABO

Multiple AllelesThe ABO blood group is a classic example of a single

gene that has multiple alleles in humans.

• Determining blood type is necessary before a person can receive a blood transfusion because the red blood cells of

incompatible blood types could clump together, causing death.

Blood Donation

• You cannot receive blood from just anyone.

• Because of this, donating blood is extremely helpful for doctors and hospitals.

Type O– blood is considered the “universal donor” because it can be donated to people of any blood type.

Type AB+ blood is considered the “universal recipient” because people with this type can receive any blood type.

The gene for blood type, gene l, codes for a molecule that attaches to the surface of red blood cells.

Different blood types have different types of molecules on the outside of their red blood cells

The ABO Blood Group

The lA and lB alleles each code for a different molecule.

Your immune system recognizes the red blood cells as belonging to you. If cells with a different surface

molecule enter your body, your immune system will attack them.

• Polygenic inheritance is the inheritance pattern of a trait that is controlled by many genes.

POLYGENIC INHERITANCE Controlled by many genes in an individual

• POLY = MANY

• GENIC = GENES

• This means there can be an ARRAY of phenotypes.

• The result is that the phenotypes usually show a continuous range of variability from the minimum value of the trait to the maximum value.

POLYGENIC INHERITANCE

• Along with skin color, examples of polygenic inheritance is hair color, eye color, and height.

• In humans the diploid number of chromosomes is 46, or 23 pairs.

• There are 22 pairs of homologous chromosomes called autosomes. Homologous autosomes look alike.

• The 23rd pair of chromosomes differs in males and females.

GENDER DETERMINATION

• These two chromosomes, which determine the gender of an individual, are called sex chromosomes and are indicated by the letters X and Y.

GENDER DETERMINATION

MALES

XY

FEMALES

XX

• Males usually have one X and one Y chromosome and produce two kinds of gametes, X and Y.

• Females usually have two X chromosomes and produce only X gametes.

• It is the male gamete that determines the sex of the offspring.

GENDER DETERMINATION

• Traits controlled by genes located on sex chromosomes are called sex-linked traits.

The alleles for sex-linked traits are written as

superscripts of the X or Y chromosomes.

Because the X and Y chromosomes are not homologous, the Y chromosome has no corresponding allele to one on the X

chromosome and no superscript is used.

X YR

Many human traits are determined by genes that are carried on the sex chromosomes; most of these genes

are located on the X chromosome.

Sex-Linked Traits in Humans

If a son receives an X chromosome with a recessive allele, the recessive phenotype will be expressed because he does not inherit on the Y chromosome.

X Y The female would have to have the recessive allele

on both of her X chromosomes for it to be expressed

X X

Recessive Sex-Linked Traits:

r

rr

Sex-Linked Traits in Humans

Two traits that are governed by X-linked recessive inheritance in humans are red-green color blindness

and hemophilia.

• People who have red-green color blindness can’t differentiate these two colors.

• Color blindness is caused by the inheritance of a recessive allele at either of two gene sites on the X chromosome.

• Hemophilia is an X-linked disorder that causes a problem with blood clotting.

Hemophilia: An X-linked disorder

• About one male in every 10 000 has hemophilia, but only about one in 100 million females inherits the

same disorder.

• Many abnormalities in the number of sex chromosomes are known to exist.

Abnormal numbers of sex chromosomes

• Any individual with at least one Y chromosome is a male, and any individual without a Y chromosome is a

female.

Turners Syndrome

• Absence of one X chromosome

• Occurs in 1 out of every 2,500 live female births.

• Physical characteristics

• No mental disability

Abnormal numbers of sex chromosomes

• Most of these individuals lead normal lives, but they cannot have children and some have varying degrees of mental retardation.

XXX

“Trisomy X”

XXY

“Klinefelter’s”

XYY

“Jacob’s Syndrome”

How do red blood cells of phenotype O differ from the cells of the other phenotypes?

Question 1

AnswerRed blood cells of phenotype O display no surface molecules.

What is the difference between simple Mendelian “simple” inheritance and co-dominant inheritance?

Question 2

If the offspring of human mating have a 50-50 chance of being either male or female, why is the ratio not exactly 1:1 in a small population?

Question 3

AnswerThe ratio is not exactly 1:1 because the laws of probability govern fertilization.