Genetics

Chapter 11

History of Genetics

Gregor Mendel 1822-1884 “Father of genetics” a monk who studied inheritance traits in

pea plans worked with pea plants in the monastery

garden

Pea plants reproduced sexually- with male and female gametes

Plants could self-pollinate and short plants bred short plants and tall plants bred tall plants.

He studied the following traits: seed color, pod shape, plant height, etc.

What Mendel noticed about his pea plants:

Mendel’s Crosses

Mendel bred plants with different traits and studied the offspring. original parents are the P generation. offspring were the F1 (daughter/son)

generation

Mendel’s conclusions

Law of Inheritance Traits are controlled by pairs of genes-

with one member of each pair coming from each parent

Law of dominance some alleles are dominant and other

are recessive. Dominant – expressed Recessive – present but not expressed

Mendel’s Laws Continued

Law of Segregation and Recombination During gamete formation two

chromosomes separate Each gamete contains one allele for each

trait

Law of Independent Assortment Traits are inherited independently of

each other

Key Terms

Gene Sections of giant DNA molecules found in

chromosomes Are the units of heredity

Allele Alternative genes for trait Example: Height: Tall or Short; Eyes:

Brown or Blue; Cheeks: Dimple or No Dimple; Hair Line: Widows or Straight

D/R

Each gene has two possible alleles Dominant- always expressed Recessive- always hidden by a dominant

allele. Example: Dimpled chin (cleft chin)

D= dimpled d= non-dimpled

More terms: Homozygous / Pure

having 2 of the same alleles example: DD – homozygous dominant

dd – homozygous recessive

Heterozygous / Hybrid having 2 different alleles ex: Dd

Phenotype physical characteristic ex: dimpled chin

Genotype genetic make up ex: DD

Punnett Square

Used to predict the possible offspring of a couple.

Gives the probability of the mating- not the actual outcome

Punnett Square Rules

Define traits, assign symbols Determine the parental genotypes Set up Punnett square Work it out List the genotype probability List the phenotype probability

Practice In humans a widow’s peak is dominant over a

straight hairline. A man who is heterozygous for widow’s peak married a woman without a widow’s peak. Predict the genotype and phenotype of the offspring:

In humans, the ability to tongue roll is dominant over not being able to tongue roll. Cross a heterozygous man with a non-rolling woman. List the possible genotypes and phenotypes of the offspring.

In humans, brown eyes are dominant over blue eyes. Cross a homozygous dominant man with a blue eyed woman. List the possible genotypes and phenotypes of the offspring.

In guinea pigs, black hair is dominant over brown hair. Cross two guinea pigs that are heterozygous for black hair. What are the chances their offspring would have brown hair?

Intermediate Inheritance

Incomplete Dominance a type of heredity in which the hybrid is

an intermediate between the pure dominant and recessive parents. (Blending of trait) Example

Co-dominance expression of two dominant alleles

(spots, strips, etc) Example

Example of Incomplete Dominance

A Japanese 4 o’clock flower can be red, white, or pink. Pink is the result of the mixture of red and white. Cross two pink flowers. List their genotypes and phenotypes.

RR = Red WW = White RW = Pink

Example of Co-dominance Shorthorn cattle can have one of three color coats. Their

coats can be red, white or roan. Roan is patches of red and white hairs. Cross a roan bull with a red cow.

CRCR = Red Hair CWCW = White Hair CRCW = Roan

Sex Linked Traits Sex Determination

Female: XX Male: XY

The sperm cell determines the sex of the child

Sex Linked Trait The gene found only on the X or Y chromosome Males tend to be more vulnerable to sex-linked

genetic disorders because most disorders occur on the X chromosome

Practice: Sex Linked Traits In humans, hemophilia is a sex linked trait.  

Females can be normal, carriers, or have the disease.  Males will either have the disease or not (but they won’t ever be carriers). Cross a male with hemophilia with a carrier female. List genotypes and phenotypes.

Multiple Alleles some traits have more than one

allele, but a single individual cannot have more than two genes for a each trait

Example: Human Blood Type Type A Type B Type AB Type O

Can you Write out the Key?

Type A and B are co-dominant Type O is recessive

Blood Type Key

PhenotypeType A

Type B

Type AB

Type O

GenotypeIAIA

IAiO

IBIB

IBiO

IAIB

iOiO

Practice: Multiple Alleles The ABO blood group system in humans is an

example of multiple alleles. Cross a heterozygous type A male with a heterozygous type B female. Record the possible genotypes and phenotypes.

Cross a person with type AB blood and a person who is heterozygous for type B blood. What are the chances the child will have type A blood?

What must the genotypes of a parent with type A blood and a parent with type B blood be if they have a child with type O blood?