Transcript Genetics - TeacherWeb

Genetics:
• Branch of biology dealing with genes
and heredity
• Genes: bits of DNA on chromosomes
• Usually 2 genes for a trait
 Dominant Gene: always seen in the
population – represented by a capital letter
 Recessive Gene: overpowered by the
dominant gene – represented by a small
letter
• Trait: a feature or characteristic (eye
color, hair color)
• Alleles: different forms of a gene on
a homologous chromosome
Gregor Mendel (1822-1884)
The “Father of Genetics”
• Austrian monk who worked with pea plants (28,000
plants in a 10 year span)
 Use of favorable material (easy to raise)
 Self-pollination (creation of pure strains) and cross-pollination
possible
 Discontinuous traits (2 contrasting forms)
 Could study 1 trait at a time
 Large numbers of offspring produced
Mendel’s Three Laws:
• Law of Dominance: One gene can mask another gene
(dominant versus recessive)
 Phenotype: the appearance of the organism
 Genotype: the arrangement of genes
 Homozygous Dominant (FF)
 Homozygous Recessive (ff)
 Heterozygous (Hybrid) (Ff)
• Law of Segregation: In gamete formation, genes are
separated
 Rule for # of gametes: 2n (n= # of hybrids)
• Law of Independent Assortment: In gamete formation,
genes separate independent of each other
 Exception: linkage (blonde hair, blue eyes)
Rules for Problem-Solving:
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Write down dominant and recessive genes
Write down parents’ genes (P generation)
Get parents’ gametes
Do the cross on a punnett square (board for
offspring possibilities – F1 generation)
• Get results and label answer
Types of Problems:
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Simple 1 trait cross
Monohybrid Cross (Ff X Ff)
Genotype: 1:2:1 Phenotype: 3:1
Simple 2 trait cross
Dihybrid Cross (FfDd X FfDd)
Phenotype: 9:3:3:1
Incomplete Dominance (3 phenotypes present)
Andalusian Fowl FF (black) ff (white) Ff (blue)
Roan Cattle FF (brown/reddish) ff (white) Ff (brown with white)
Four O’Clock Flowers FF (red) ff (white) Ff (pink)
• Multiple Alleles: traits with more than one pair of
alleles
 Examples: Rabbits (coat color) Humans (blood groups)
• Human Blood Groups
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Karl Landsteiner
Also called Codominance (2 dominant alleles/1 recessive allele)
A and B = dominant
O = recessive
4 Human Blood Types: A B AB O (phenotypes)
Type A: AA AO (genotypes)
Type B: BB BO (genotypes)
Type AB: AB (genotype)
Type O: OO (genotype)
• Test Cross: used to determine the genotype of an
organism
 Use homozygous recessive X the unknown genotype
• 1903 Walter Sutton: factors as genes
• 1909 Thomas Hunt Morgan: Colombia University - used
Drosophila melanogaster as a research animal
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Easy to raise
Eat simple food
Life cycle (10-15 days) many generations
Easy to distinguish the sexes
4 pairs of chromosomes (3 pairs of autosomes)
Large salivary gland chromosomes
Easy storage
1 pair of sex chromosomes with sex-linked traits (white eyes) XX,
XY
• Genetic Maps: specific location of genes on
chromosomes
 Crossing over of genes (“jumping genes”)
 Barbara McClintock: research with corn
Mutations
• A change in DNA (a “mistake” in DNA)
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Add diversity
Most are recessive
Not usually positive
Inherited
Caused by mutagens (chemicals, food additive, radiation,
viruses)
• Somatic Mutation: in body cells (not passed on)
• Germ Mutation: in sex cells (passed on)
• Gene Mutation:
 Deletion (a gene is omitted)
agethol
 Insertion (a gene is added)
agethol
 Frameshift (a section is reversed) agethol
agetol
agethoyl
aolgeth
• Chromosomal Mutation:
 Inversion: piece of a chromosome breaks off and reattaches
itself to the same chromosome backwards
 Translocation: piece of one chromosome breaks off and
reattaches itself to a different chromosome
(Stillbirths)
• Human chromosome number = 46 (2n)
 n = # of chromosomes in a sperm or egg
• Aneuploidy = 1+ or - the 2n number (either 45 or 47
chromosomes)
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Monosomy: 45 (2n-1)
Turner’s Syndrome (X_) Sterile female underdeveloped
Trisomy: 47 (2n+1)
Down’s Syndrome (extra #21 chromosome)
Kllinefelter’s Syndrome (XXY) Sterile male feminized
(XYY) Tall male with acne (criminal tendencies)
(XXX) Fertile female (mentally challenged)
• Polyploidy: whole sets of chromosomes are
inherited (3n, 4n, etc.) plants
• Human chromosome number = 46 (2n)
 n = # of chromosomes in a sperm or egg cell
 Sex Linked Condition: recessive abnormality on the X
chromosome Hemophilia: XHXH XHXh XhXh
XHY XhY
 Colorblindness XCXC XCXc XcXc XCY XcY
 Sex Influenced Condition: not sex linked; not attached to the
X chromosome; patterned baldness (influenced by female
hormones)
• Genetic Abnormalities:
 PKU: affects infants; lack an enzyme; problems with amino
acids
 Sickle Cell Anemia: Pain at joints, fatigue; affects Black
Americans; red blood cell shape of sickle; (1 in 500 is a carrier)
 Cystic Fibrosis: Caucasian disease; excess mucus during
digestion
 Tay Sachs: Jewish infants (1 in 3 is a carrier)
 Galactosemia: problems with sugar breakdown
 Huntington’s Disease: causes insanity; dominant gene
• Genetic Counseling:
 Sonagrams of fetuses
 Amniocentesis: technique in which amniotic fluid is extracted and
examined
 Karyotype: a picture of the chromosomes
 Pedigree: a family history of genes
• Genetic Engineering:
 Cloning/Gene splicing
 Human Genome Project
 “Green Revolution”