classical genetics lecture
TRANSCRIPT
Classical Genetics
The Work and Conclusions of Gregor Mendel
Father of genetics
Monk in Austria
1865
Studied patterns of inheritance in peas
Why Peas?
Why Peas?
Self-fertilization produces true breeding generations
•Prevented self-fertilization
•Manipulated reproduction
•Began monohybrid crosses
•Carefully examined results
Why Peas?
Read Concept 1
Click Animation and View
Mendel’s Work
Some traits are dominant and some are recessive
Read concept 3
Click animation and view
Read concept 4
Click animation and view
Mendel’s Work
1. Traits are passed on by factors (genes)
2. Factors (genes) have more than 1 form called alleles
3. There are at least 2 alleles for each trait
Mendel’s Work
Alleles are represented by the first letter of the dominant trait
Pea plant flower color (trait)
Purple or white
Purple is dominant over white
Alleles are represented as
P=purple p=white
You try a few…
1. Round seeds are dominant over wrinkled seeds
2. Yellow seeds are dominant over green seeds
3. Tall plants are dominant over short plants
1. R=round r=wrinkled
2. Y=yellow y=green
3. T=tall t= short
Mendel’s Work
Mendel’s WorkDescribing Traits (Tall or short plants)
Genotype
The actual genetic make-up of an organism
the “genes”
Phenotype
The physical appearance or form observed
the “physical”
Mendel’s WorkPossible Genotypes (TT Tt tt)
Homozygous
The two alleles for the trait are identical
TT homozygous dominant (purebred dominant)
tt homozygous recessive (purebred recessive)
Heterozygous
The two alleles for the trait are different
Tt heterozygote (hybrid)
Mendel’s Work
Mendel’s Work
Read Concept 5
Click animation and view
Complete visual organizer of Mendel’s pea plant experiment
1. Law of Dominance
Alleles for a trait are either dominant or recessive
The dominant form is expressed and the recessive form is hidden
The only way to express a recessive trait is if there are two copies of the recessive allele
Mendel’s Conclusions
Mendel’s Conclusions
2. Law of Segregation
The two alleles for a trait separate during gametogenesis
Test Cross
Dihybrid Cross
Mendel’s 3rd Law of Independent Assortment
• Alleles of different genes are assorted independently of one another during the formation of gametes
• This means that calculating the probability of several traits appearing together is the product of the probability of each trait taken separately
• The Rule of Multiplication
Incomplete Dominance
“Dominant” gene does not fully express itself to mask the effect of the recessive gene
A pattern of inheritance in which the phenotype of a heterozygous individual is intermediate between those of the parents
Genotypic ratio is equal to phenotypic ratio
Co-DominanceTwo or more alleles are fully dominant
When present together they are both expressed
ABO Blood Groups exhibit co-dominace
Type A Blood
•Individuals with group A blood have red blood
cells with antigen A on their surface. •Produce antibodies against antigen B,
antibody B.
•Therefore, a group A person can only receive
blood from people in groups A or O
Type B Blood• Antigen B is on their cells, and
antibodies A are produced in their serum.
• A group B person can only receive blood from people in groups B or O, preferably B.
Type AB
• Individuals with group AB blood have red blood cells with both antigens A and B.
• Do not produce antibodies A or B against either antigen in their serum.
• A person with type AB blood can receive blood from any group (preferably AB) but cannot donate blood except to another AB (universal recipient).
Type O
• Individuals with group O blood have red blood cells with neither antigen A or B.
• Produce antibodies A and B against both types of antigens.
• A group O person can only receive blood from group O (universal donor).
Sex Inheritance
Sex Chromosomes X or Y
XX is female
XY is male
Read concept 9
Click animation and view
Sex-Linked Inheritance
Genes linked to sex chromosomes
GENETICGENETIC DISORDERS
Sources of Genetic Disorders• Chromosome Mutations
• Change in the genetic material on the chromosome
• Four types of chromosome mutations– Deletion, duplication, translocation and
inversion
• Change in chromosome number• Failure of homologous chromosomes to
separate during meiosis–Non-Disjunction
Deletion
• One or more genes are lost from a chromosome during division
• Occurs if homologous chromosomes cross over unequally during meiosis
Duplication
• Chromosome receives an extra piece, which duplicates some genes
Translocation
• A whole chromosome or piece of chromosome attaches to a chromosome in a different pair
• Results in extra or lost genes
• May break up important gene arrangements and change the phenotype of the organism
Inversion
• Part of chromosome breaks off and reattaches itself in reverse order
• May cause no change because it is not losing genes
• Changes the arrangement and may upset important gene interactions
Nondisjunction
• Failure of chromosome to separate during division– Mitosis
• Cell dies, organism is not harmed
– Meiosis
• Results in an abnormal gamete that will produce abnormal offspring
Turner Syndrome• XO
• phenotype-female
• small functioning ovaries
• short
• no breast development
Down Syndrome• Extra chromosome at the 21st position
• Enlarged tongues
• Small, round ears • Heart defects
• Stubby fingers and toes
• Mental retardation
Klineflelter Syndrome
• XXY at 23rd position
• small testes, no sperm development
• enlarged breast development
• tall stature
Cri-du-chat• Partial deletion from
chromosome # 5• Baby’s cry sounds like a
cat• Severe mental
retardation• Multiple anatomical
malformations
Sex-linked Disorders
Hemophilia
• mental retardation
• enlarged liver
• flat broad nose, large tongue
• inability to clot blood properly
• bruise easily
• many patients have been infected
with AIDS
Hunters Syndrome
Autosomal Dominate Disorders
Neurofibromatosis
• Disorder of connective tissue
• Affects bone, eyes, heart and blood vessels
• Long legs and hands
• Blood vessels lack elasticity
• Can be slight to severe• Tumors on head, neck, and spine
Marfan Syndrome
Huntington Disease• Progressive degeneration of brain cortex • Symptoms begin around the age of 30-50• Symptoms include
• depression• forgetfulness• clumsiness• twitching• mood swings
Autosomal Recessive Disorders
Porphyria
• Prophyrin build-up(molecules formed during the synthesis of hemoglobin)• “werewolf”• emotionally unstable• sensitive to light• self mutilation
Cystic Fibrosis
• very common, 40% of population are carriers
• disease of exocrine glands, build up of thick mucus in the lungs that makes breathing difficult
• causes respiratory infections
Leprechanism
• Short, elf-like appearance
• Hypoglycemia
Progeria• Premature aging
• Die of artery disease at age 10-15