1. Mendel’s Laws of Heredity
Why we look the way we look...

2. What is GENETICS? Genetics: the study of heredity
Heredity: The passing on of characteristics (traits) from parents to offspring

3. Examples of Dachshund Traits Type of fur coat: smooth, long, wire
Trait – A particular characteristic that can vary from one individual to another. Ex: hair color
Examples of Dachshund Traits
Type of fur coat: smooth, long, wire
Color of fur coat: red, tan, black, silver

4. Fertilization
Review!
Fertilization: the joining of one male and one female gamete (reproductive cells) during sexual reproduction

5. GENES
Genes - Section of a chromosome that determine the trait that will be inherited Ex: Sally has the gene for brown hair
Each person two genes for each trait, one gene comes from mom, one from dad.
Alleles - Different forms of one gene
Ex: Brown, red, or blond hair are all different forms the hair color gene

7. Rule of Dominance
Dominant gene: Always expressed if present for a trait
Represented by a capital letter; “B” is for brown eyes. A brown-eyed organism could be BB or Bb to be dominant. The B for Brown eyes overpowers the b for blue eyes and so the organism displays the Brown eye trait.
Recessive gene: Only expressed if two alleles are present for that trait
Represented by a lowercase letter. “b” is for blue eyes. Organism must have genes bb to have blue eyes.

8. PRACTICE! 1. T T 2. t t _____ 3. T t 4. S S 5. s s _____ 6. S s
Dominant
Recessive
Dominant
Dominant
Recessive
Dominant

9. Homozygous vs. Heterozygous
Homozygous: Organisms have 2 identical (same) alleles for a trait
BB is homozygous dominant for brown eyes
bb is homozygous recessive for blue eyes
Heterozygous: Organisms have 2 (different) alleles for a trait
Bb is heterozygous for brown eyes

10. Homozygous vs. Heterozygous

11. PRACTICE! 1. AA 2. Aa 3. Mm 4. gg 5. GG 6. Gg Homozygous Heterozygous

12. Phenotypes and Genotypes
Genotype: (genes) the genetic makeup or combination of alleles (1 from mom & 1 from dad)
Ex. BB, Bb, bb
Phenotype: physical characteristics of the trait
Ex. Brown hair, blue eyes (what you see)

13. Genotype - always use the letter of the dominant trait first. Ex
Genotype - always use the letter of the dominant trait first. Ex. Straight hair is dominant to curly hair Straight hair is dominant = capitol S Curly hair is recessive = lowercase s Genotype for straight hair = SS or Ss Genotype for curly hair = ss

14. A History of Genetics: Gregor Mendel
Austrian monk
Known as the Father of Genetics
Cross-bred common pea plants to study the inheritance of traits through each generation.

15. Mendel’s Conclusions
Biological Inheritance is passed from one generation to the next.
Your traits are determined by genes passed toyou from your parents.
Law of Segregation
During Meiosis, the pairs of genes separate so that each gamete receives only one gene for each trait
Law/Principal of Dominance
Some alleles are dominant and some are recessive.
Recessive traits will only show up if the dominant allele is NOT present

17. Punnett Squares
Punnett Square - a diagram used to predict the outcome of a particular cross or breeding experiment. Used to determine the probability (chance) of EACH offspring’s genotypes and phenotypes. Does NOT determine how many offspring will be produced or exactly what the offspring’s genotype and phenotype will be…just the chances!

18. Punnett Squares There are five steps (you must always show your work)
Key- List the trait, Both alleles, and which phenotype corresponds with each allele
Parents- List the genotypes of each parent
Draw the punnett square
Determine the genotype ratio
Determine the phenotype ratio

19. WW Ww Ww ww 1.W= wavy hair w= straight hair W w W w 2 3 2
ww = straight
Genotype Ratio 1:2: 1
Phenotype Ratio 3:1 2 4 5

20. Practice Monohybrid Punnett!
Cross a female heterozygous dominant brown eyes with a male homozygous recessive blue eyes X
Possible Phenotypes:
Possible Genotypes:
Ratio: Percent:

21. Practice Monohybrid Punnett!
Cross a female heterozygous dominant brown eyes with a male homozygous recessive blue eyes X B b Bb bb
Possible Phenotypes: Brown & Blue
Possible Genotypes: Bb, bb
Ratio: 1:1 Percent: 50% Brown
50% blue b Bb bb b Bb bb