1. Genetics
Chapter 12

2. 12-1: Origins of Hereditary Science

3. Mendel’s Experiments
Genetics – The study of how characteristics are transmitted from parents to offspring
Heredity – The passing on of genetic characteristics from one generation to another

4. Mendel’s Experiments
Gregor Mendel (an Austrian monk) used cross-pollination techniques in which pollen is transferred between flowers of two different plants.

5. Mendel’s Experiments Reasons Mendel used pea plants
Require little care
Produce many offspring
Mature quickly (8-10 weeks)

6. Mendel’s Experiments
P (parental) generation – Organisms that are true-bred for specific traits
F1 generation – Offspring of the P generation
F2 generation – Offspring of the F1 generation
F = Filial (pertainting to a son or daughter)

7. Mendel’s Experiments
Self-pollination – A plant with both male and female reproductive organs that fertilizes itself
Cross-pollination – Pollen from one plant is carried to the flower of another plant

8. Mendel’s Experiments
Three Steps of Mendel’s Experiments

9. Mendel’s Experiments
Gene – A section of DNA that carries the information on how to make one protein

10. Mendel’s Experiments Allele – An alternative form of a gene
One allele for each trait is passed from each parent to the offspring.

11. Mendel’s Experiments
Dominant trait – An allele that is fully expressed whenever the allele is present in an individual
The trait that masks the other
Recessive trait – An allele that is expressed only when there is no dominant allele present in an individual
The trait that is masked

12. 12-2: Genetic Crosses

13. Monohybrid Cross
Monohybrid cross – A cross in which one characteristic is tracked
Punnett square – used to predict the outcome of genetic crosses

14. Monohybrid Cross
Genotype – the genetic makeup of an organism (use letters)
Phenotype – the appearance of an organism (physical appearance)

15. Monohybrid Cross Homozygous – having identical alleles
Heterozygous – having different alleles

16. Monohybrid Cross Trait – Plant height Phenotype Genotype T – tall
t – short
Genotype
TT – homozygous dominant (pure bred)
Tt – heterozygous (hybrid)
tt – homozygous recessive (pure bred)

17. Monohybrid Cross
Probability – the likelihood that a specific event will occur
Probability = number of one kind of possible outcome
total number of all possible outcomes
A probability may be expressed as a decimal, a percentage, or a fraction

18. Mendel’s Characteristics

19. Monohybrid Cross Ratios and percentages TT x tt = 100% heterozygous
TT x TT = 100% homozygous dominant
tt x tt = 100% homozygous recessive
Tt x tt
50% heterozygous
50% homozygous recessive

20. Monohybrid Cross Ratios and percentages
Tt x Tt = Genotypic ratio – 1:2:1 ratio
25% homozygous dominant
50% heterozygous
25% homozygous recessive
Tt x Tt = Phenotypic ratio – 3:1
75% tall
25% short

21. Dihybrid Cross
Dihybrid cross – A breeding experiment that tracks the inheritance of two traits
Example
Traits: Seed shape & Seed color
Alleles: R – round r – wrinkled Y – yellow y – green

22. Dihybrid Cross RrYy x RrYy
Use the FOIL method for each parent to set-up the Punnett square
RrYy x RrYy
RY Ry rY ry
RY Ry rY ry

23. Dihybrid Cross RY Ry rY ry RY Ry rY ry

24. Dihybrid Cross RY Ry rY ry Round/Yellow: 9 Round/green: 3
Mendelian Genetics
4/23/2017
Dihybrid Cross RY Ry rY ry
Round/Yellow: 9
Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1 phenotypic ratio
RRYY
RRYy
RrYY
RrYy
RRyy
Rryy
rrYY
rrYy
rryy 24 24

25. Why eye color changes in people is unknown
The trait for eye color actually has three alleles:
AaBbCc
This chart is used to illustrate the variety of eye colors

26. Other Monohybrid Crosses
Incomplete dominance – a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele
This results in a combined phenotype.

27. Other Monohybrid Crosses
Codominance – Two alleles are expressed (multiple alleles) in heterozygous individuals
Two alleles that are both dominant
Example: blood types
Key
A = IA
B = IB
O = I
A and B are dominant over O

28. Other Monohybrid Crosses
Genotypes Phenotypes
Type A = IAIA or IAi AA or AO
Type B = IBIB or IBi BB or BO
Type AB = IAIB AB
Type O = ii OO

29. Other Monohybrid Crosses
Sex-Linked traits – Traits (genes) located on sex chromosomes
X – Female sex chromosome
Y – Male sex chromosome
Many sex-linked traits carried on X chromosome

30. Pedigree
Pedigree – A diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships