1. Fundamentals of Genetics

2. 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

3. 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

4. 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. 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)

7. 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.

8. 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

9. 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.

10. 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)

11. 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.

12. 9. Monohybrid Crosses (Examples)
Ex 1: Pure Tall (TT) x Pure Short (tt)
TT=Tall
tt =short F 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)

13. 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

15. STOP

16. 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

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

18. 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

20. RED
WHITE
ROAN

21. 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

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

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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