Upload
clifford-barber
View
221
Download
0
Tags:
Embed Size (px)
Citation preview
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?