Fundamentals of Genetics

Fundamentals of Genetics

Introduction to Genetics 1. GREGOR MENDEL - “Father of Genetics” Austrian monk, teacher, scientist, gardener Formulated basic laws of heredity in the early 1860s Simplified problems; was meticulous with data collection; think quantitatively

2. Worked with garden peas because: Easy to grow and had a short generation time Could be self-pollinated 3. Chose true-breeding varieties for his experiments Means no genetic variation for a trait Studied 7 simple traits

P1 = parental generation F1 = first-generation (sons/daughters) 4. Mendel cross-pollinated plants P1 = parental generation F1 = first-generation (sons/daughters) F2 =second-generation

5. Principle of Dominance and Recessiveness F1 plants resembled only one of the parents F1 hybrids contained two factors for each trait one dominant; (stronger, masks recessive); one recessive; (seems to disappear)

6. Principle of Segregation Organism contains two factors for each trait. Factors segregate during formation of gametes. Each gamete contains one factor for each trait.

7. Principle of Independent Assortment Each trait is independent of another Genes of one pair of traits assort independently All combinations of genes occur in gametes

Chromosomes, Genes, and Genetic Crosses Homologous Chromosomes contain genes (locations) for the same traits Traits are controlled by alleles (alternative forms of a gene). Genotype refers to the alleles an individual receives at fertilization Phenotype refers to the physical appearance of the individual.

5. Homozygous dominant genotypes = two dominant alleles for a trait. (BB) 6. Homozygous recessive genotypes = possess two recessive alleles for a trait (bb) 7. Heterozygous genotypes = one of each allele for a particular trait (Bb)

Show probabilities of future offspring 8. Punnett Squares Show probabilities of future offspring Monohybrid crosses = crosses between individuals that involve one pair of contrasting traits.

9. Monohybrid Crosses (Examples) Ex 1: Pure Tall (TT) x Pure Short (tt) TT=Tall tt =short F1 F2 T T t Tt Tt T t T t TT tt 25% pure tall 50% hybrid tall 25% pure short 100% Tall (Homozygous x Homozygous) (Heterozygous x Heterozygous)

10. Test Crosses A cross of an individual of unknown genotype with an individual of known genotype Tells if individual is heterozygous or homozygous Very important to breeders

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Dominance Has Degrees 1. Incomplete dominance Offspring are intermediate between two parental phenotypes Neither allele is completely dominant over the other Both alleles influence phenotype 3 phenotypes

Ex: Japanese Four o’clocks RR = red RR’ = pink R’R’ = white All Pink 1 red : 2 pinks : 1 white

2. Codominance Both alleles of a gene are expressed. A person with AB blood has both A and B antigens on their red blood cells. Neither allele is dominant or recessive

RED WHITE ROAN

White & Red Mixed – RW (“roan”) Ex: Red Coat - RR White Coat – WW White & Red Mixed – RW (“roan”) R R R W RW RW RW R W RR W RW RW RW WW All Roan – both red and white hair 1 red : 2 roan : 1 white

Dihybrid Cross A cross involving two pairs of contrasting traits Example: Dominant Yy, YY = yellow Rr, RR = round Recessive yy = green rr = wrinkled

Nondisjunction occurs when a chromosome pair fails to separate properly during meiosis-can happen to any chromosome pair 2 types: 1. Monosomy: when gamete has one less chromosome than it should only 45 chromosomes (need 46) Ex: Turner syndrome-occurs only in females 2. Trisomy: when gamete has one more chromosome than it should 47 chromosomes( need 46) Ex: Down’s syndrome, extra #21 Don’t forget: you have 23 pairs(46 chromosomes) in each cell in your body

Aneuploidy (abnormal number of chromosomes caused by Nondisjunction) Disorder: Down’s Syndrome (Trisomy 21) Facts: most common reason for mental retardation; chromosome pair #21 failed to separate Symptoms: mental retardation, slanted eyes Incidence: 1 in 900; most cases not inherited Treatments: none

Aneuploidy (caused by Nondisjunction/ Trisomy) Disorder: Klinefelter Syndrome Facts: XXY - Trisomy- sex chromosomes failed to separate in meiosis Symptoms: male, taller than average, longer limbs, sterile, may have some mental retardation Treatments: none

Aneuploidy (caused byNondisjunction/Monosomy) Disorder: Turner’s Syndrome Facts: female, only 1 X because of Nondisjunction Symptoms: sterile, lack of sexual development (no ovaries), short stature Treatments: none

Sex-linked Disorders. write Xm Xm , XmY Sex-linked Disorders *write Xm Xm , XmY *most disorders are x-linked, recessive Disorder: Muscular Dystrophy (MD) (duchenne’s only) Facts: recessive, x-linked; many types of MD Symptoms: muscle loss & weakness Incidence: mainly in males; all ethnic groups have an equal chance of MD Treatments: physical therapy , braces, wheelchair

Sex-linked Disorders Disorder: Hemophilia Facts: recessive, x-linked; blood does not have clotting factors Symptoms: bleed excessively or to death Incidence: mainly in males ; Royal Family Treatments: inject themselves with purified clotting factors to prevent or stop bleeding

Sex-linked Disorders Disorder: Color-blindness Facts: recessive, x-linked disorder; Cones in eyes(color receptors) are absent or lack of pigment Symptoms: cannot tell difference between certain colors Incidence: mainly in males- passed from mother; red-green color blindness most common Seeing only black/white is rare Treatments: none