1. Introduction to Genetics

2. Heredity
The passing on of characteristics from parents to offspring

3. Traits
Characteristics that are inherited

4. Genetics The study of heredity
Genes: chemical factors that determine traits
Can occur in 2 different forms called alleles

5. Gregor Mendel Father of genetics
1st to succeed in predicting how traits would be transferred from one generation to the next
Used pea plants
Pea plants reproduce sexually
Produce male and female sex cells (gametes)
Fertilization: male and female gametes unite, resulting in a zygote (fertilized egg)

6. Controlled plant crosses by removing male parts
Mendel studied only 1 trait at a time (7 total traits)
True-breeding pea plants:
Produced identical offspring
Ex: tall or short, green or yellow

7. Organisms can look alike but have different combinations of alleles
Crossed a tall plant with a short plant
Parent generation (P1)
Offspring called hybrids (F1)
Have different forms of a trait
Showed characteristics of only 1 parent
Observed traits are dominant
Traits that seem to disappear are recessive
Allele for tall plants is dominant to the allele for short plants
Inherit one gene from mom and one from dad
Organisms can look alike but have different combinations of alleles
Different forms of a gene for each variation of an inherited trait

8. Phenotype: way an organism looks and behaves
Physical characteristics
Ex: height (tall, short), skin color (red, white, blue..etc), head size, eye color…etc
Genotype: Allele combination an organism contains
Genetic make-up
Assigned a letter to represent the trait
Ex: TT, Tt, tt

9. Homozygous: 2 alleles for the trait are the same
Called true-breeding
Ex: TT, CC, HH, tt, cc, hh
Heterozygous: 2 alleles for the trait differ from each other
Called hybrids
Ex: Tt, Cc, Hh, Ss

10. Punnett Squares
Way to find expected proportions or probability of possible genotypes in the offspring of a cross
Probability
Likelihood an event will occur
Used to predict outcomes of a genetic cross
Way alleles separate is random
Cannot give actual outcome

11. Monohybrid cross (mono-: means one)
Focus on 1 trait
Ex: height T= tall, t= short
texture S= smooth vs. s= rough,
Crossed a tall plant with a short plant

12. Mendel’s Crosses 1st generation plants (F1) were all tall
Self-pollinated to make 2nd generation plants (F2)
2nd generation plants:
¾ were all tall plants
¼ were short plants

13. ex: First generation plants (F1): all tall

14. ex: Second generation plants (F2)
Punnett squares are good for showing all the possible combinations of alleles and the probability of inheriting a trait

15. Bell Ringer:
Which 2 combinations of alleles could produce a trait controlled by a dominant allele?
What combination of alleles could produce a trait controlled by a recessive allele?
If a heterozygous plant for seed color (Rr) is crossed with a homozygous recessive plant (rr), what is the probability of each seed color being produced? Draw a punnett square to show work.
Organisms that have identical alleles for a particular trait are:
a. heterozygous b. polygenic
c. diploid d. homozygous

16. Dihybrid Crosses (di-: means 2)
Involve two traits
Mendel: used seed color and seed texture
Crossed round yellow seeds (RR and YY) with wrinkled green seeds (rr and yy)
Round is dominant to wrinkled
Yellow is dominant to green
1st generation (F1) plants: round and yellow (RrYy)
2nd generation (F2) plants:
round yellow (9)
round green (3)
wrinkled yellow (3)
wrinkled green (1)

17. Rule of Dominance Some alleles are dominant and others are recessive
Pea plants with 2 alleles for tallness were tall
Pea plants with 2 alleles for shortness were short
Dominant allele: observed trait
Upper-case letters = Dominant allele (always put capital letter 1st for the genotype)
Ex: allele for tallness (T)
Tall Plants: TT or Tt
Recessive allele
Lower-case letters = Recessive allele
Always listed after the dominant allele
Will only appear if no dominant allele is present
Ex: allele for shortness (t)
tt  short plant
Disappears

18. Law of Segregation Every individual has 2 alleles of each gene
When gametes are produced, each gamete receives 1 of these alleles
Randomly pair to produce 4 combinations of alleles during fertilization
Tall plant: Short plant:
TT x tt = Tt
Yellow plant x Green plant:
YY x yy = Yy

19. F1 generation Tt Tt Tt X
gametes T t T t TT Tt Tt tt
F2 generation

20. Law of Independent Assortment
Ex: Does a gene that determines whether a seed is round or wrinkled have anything to do with seed color?
Genes do not have to be carried together
Travel independently
Genes for different traits can segregate independently during formation of gametes
Accounts for the wide variety of genetic combinations in offspring
Genes for different traits are inherited independently of each other

21. Incomplete Dominance “blend” or mixing of traits
neither allele is completely dominant
phenotype of heterozygous individuals is intermediate (in the middle)
mix of purebred phenotypes
ex: Red flowers (RR) x White flowers (R´R´) = Pink flowers (RR´)

22. Codominance phenotypes of both homozygotes are produced
both are dominant
both alleles contribute to the phenotype but do not blend together
both alleles are expressed equally
ex: chickens
Black chickens (BB) x White chickens (WW) = checkered or speckled chickens (BW)
ex: red cow (RR) x white cow (WW) = roan cow (pinkish brown  RW)
ex: Sickle-Cell anemia

23. Multiple Alleles Genes with more than 2 alleles
Ex: rabbit coat color, blood type, eye color

24. Polygenic Inheritance
inheritance pattern of a trait that is controlled by 2 or more genes
may be on the same or different chromosome
each gene can have 2 or more alleles
ex: skin color, fruit fly eye color

25. Bell Ringer: a. segregation b. true-breeding
1. According to the principle known as _______, genes that segregate independently do not influence each other’s inheritance.
2. The separation of alleles during gamete formation is called ____.
a. segregation b. true-breeding
c. meiosis d. crossing-over
3. Which of the following structures assort independently?
a. genes b. crossovers c. chromosomes d. genotypes
4. Genes on the same chromosome
a. never separate b. sometimes separate
c. always separate d. don’t show linkage

26. Applying Mendel’s Principles
Thomas Hunt Morgan (1900’s)
Studied fruit flies
Observed fruit flies produce a lot of offspring quickly
Mendel’s principles apply to all living organisms

27. Linkage and Gene Maps Each chromosome is a group of linked genes
Chromosomes assort independently (not individual genes)
Genes can separate by crossing-over
Gives genetic diversity
More likely to be separated the further apart they are on the chromosome

28. Gene map
Shows locations of known genes on a chromosome

29. Simple Dominant Heredity
Only need to inherit 1 dominant allele to display the trait
Tongue rolling
Free earlobes
Hitchhiker’s thumb
Dimples
Cleft chin
Freckles

30. Bell Ringer: a. polygenic trait b. punnett square
Which of the following shows the relative locations of each known gene in an organism?
a. polygenic trait b. punnett square
c. gamete d. gene map
2. Match the type of inheritance with its correct description:
incomplete dominance codominance
multiple alleles polygenic traits
_______ both alleles contribute to the phenotype of the organism
_______ more than two possible alleles for a trait exist in a population
_______ traits controlled by two or more genes
_______ one allele is not completely dominant over the other allele