1. Intro…GENETICS
MENDEL & MEIOSIS

2. MENDEL’S LAWS OF HEREDITY
Gregor Mendel – father of genetics
The characteristics passed on called traits

4. Used garden peas for a model organism
Have male & female gametes (sex cells)
sperm egg in/on same flower
Mendel controlled the fertilization process
Not many traits to keep track of

6. MENDEL WAS A CAREFUL RESEARCHER
USED CAREFULLY CONTROLLED EXPERIMENTS
STUDIED ONE TRAIT AT A TIME
KEPT DETAILED DATA

8. MONOHYBRID CROSSES 7 TRAITS in peas
seed shape/color, flower color/position, pod color/shape, plant height
Crossed plants w/ diff. traits to see what traits the offspring would have
Tall with Short ??
Green peas with Yellow peas ??
Purple flowers with White Flowers ??
A monohybrid cross is one that looks at only one trait

9. THE 1ST GENERATION Crossing two plants – 1 tall & 1 short
All the offspring are tall !!
Draw the Punnett Square now
VOCAB:
gene homozygous dominant
allele homozygous recessive
heterozygous
genotype
phenotype

10. THE 2ND GENERATION
Cross two plants from the F1 generation to make the F2 generation
SHOW THIS CROSS
¾ of the offspring were tall & ¼ were short The short plants reappeared !!

13. Independent Assortment
Laws:
Independent Assortment
Segregation
VOCABULARY:
Allele
Genotype
Phenotype
Dominant
Recessive
Trait
Heterozygous
Homozygous

14. ALLELES, DOMINANCE, & SEGREGATION
Genes – a stretch of DNA that codes for a protein. Again DNA->mRNA->protein->trait
The genes Mendel studied came in two forms (tall/short - round/wrinkled yellow/green…….etc.)
Alternate forms of a gene are called alleles
Alleles are represented by a one or two letter symbol (e.g. T for tall, t for short)

16. ALLELES CONT’D These 2 alleles are found on copies of CHROMOSOMES.
You get one allele (one copy of each gene) from each parent.

17. THE RULE OF DOMINANCE
A dominant trait is the trait that will always be expressed if at least one dominant allele is present.
The dominant allele is always represented by a capital letter. Ex: T
A recessive trait will only be expressed if both alleles are recessive. Ex: tt
Recessive traits are represented by a lower case letter Ex: t

18. DOMINANCE CONT’D LET’S USE TALL & SHORT PEA PLANTS FOR AN EXAMPLE
WHICH OF THESE WILL SHOW THE DOMINANT & RECESSIVE TRAIT?
TT Tt tt
DOMINANT TRAIT RECESSIVE TRAIT

19. THE LAW OF SEGREGATION
Mendel asked himself… “How did the RECESSIVE short plants reappear in the F2 GENERATION?”
He concluded that each TALL plant from the F1 generation carried TWO ALLELES, 1 dominant tall allele & one recessive short allele.
So all offspring were Tt

20. SEGREGATION CONT’D
He also concluded that only one allele from each PARENT went to each OFFSPRING
HIS CORRECT HYPOTHESIS WAS THAT SOMEHOW DURING FERTILIZATION, THE ALLELES SEPARATED (SEGREGATED) & COMBINED WITH ANOTHER ALLELE FROM THE OTHER PARENT
The law of segregation states that during gamete formation, the alleles separate to different gametes

21. - the law of segregation explained the heredity of the f2 generation
FATHER
MOTHER
F1 GENERATION
T t
T t
t t
T T
T t
F2 GENERATION
- the law of dominance explained the heredity of the offspring of the f1 generation
- the law of segregation explained the heredity of the f2 generation

24. PUNNETT SQUARE
CROSS T T X Tt

25. CONT’D
T T X T t T T T T T T T t T t T t

26. PHENOTYPES & GENOTYPES
PHENOTYPE – The Physical appearance – how an organism looks – the Trait
GENOTYPE – the Allele combination…Aa or AA or aa…….also Ttyy or ttyy or TTYY
HOMOZYGOUS – 2 ALLELES SAME
HETEROZYGOUS – 2 ALLELES DIFFERENT
Like Homo-Sexual… Hetero-Sexual
Same gender couple Different gender couple

27. ANSWER ON YOUR SHEET TRAITS = BLUE SKIN & YELLOW SKIN
BB – IS THIS HOMOZYGOUS OR HETEROZYGOUS?
IS BLUE SKIN OR YELLOW SKIN DOMINANT?
HOMOZYGOUS
BLUE

28. MENDEL’S DIHYBRID CROSSES
MONOHYBRID – MENDEL LOOKED AT ONE TRAIT
IN HIS DIHYBRID CROSSES – HE LOOKED AT 2 TRAITS
WANTED TO SEE IF TRAITS ARE INHERITED TOGETHER OR INDEPENDENTLY

29. ALL THE OFFSPRING ARE ROUND
DIHYBRID CROSS
TOOK TWO TRUE BREEDING PLANTS FOR 2 DIFFERENT TRAITS (ROUND/WRINKLED SEEDS YELLOW/GREEN SEEDS)
1ST GENERATION
WHAT WOULD HAPPEN IF HE CROSSED JUST TRUE BREEDING ROUND W/ TRUE BREEDING WRINKLED (ROUND IS DOMINANT)
ALL THE OFFSPRING ARE ROUND

30. DIHYBRID CROSS – 1ST GENERATION CONT’D
SO WHAT DO YOU THINK HAPPENED WHEN HE CROSSED TRUE BREEDING ROUND/YELLOW SEEDS WITH TRUE BREEDING WRINKLED/GREEN SEEDS
ALL THE F1 WERE ROUND AND YELLOW

31. DIHYBRID CROSS – 2ND GENERATION
TOOK THE F1 PLANTS AND BRED THEM TOGETHER (PHENOTYPE WAS ROUND/YELLOW X ROUND/YELLOW)
2ND GENERATION
FOUND ROUND/YELLOW
FOUND ROUND/GREEN
FOUND WRINKLED/YELLOW - 3
FOUND WRINKLED/GREEN
( 9 : 3 : 3 : 1 RATIO)

32. EXPLANATION OF 2ND GENERATION
MENDEL CAME UP W/ 2ND LAW – THE LAW OF INDEPENDENT ASSORTMENT
Genes for different traits (Pea color, and flower color) are inherited independently of each other
Just because you have brown hair, doesn’t mean you will be short!

33. DIHYBRID CROSSES A LITTLE DIFFERENT H h G g X H h G g
What are the possible Allele combinations?
USE THE FOIL METHOD
First, Outer, Inner, Last

34. H h G g X H h G g 1. HG BOTH PARENTS ARE THE SAME 2. Hg 3. hG 4. hg
FOIL – FIRST, OUTSIDE, INSIDE, LAST
H h G g X H h G g
1. HG
BOTH PARENTS ARE THE SAME
2. Hg
3. hG
4. hg

35. NOW LET’S DO A DIHYBRID CROSS
H h G g X H h G g HG Hg hG hg HG
HHGG
HHGg
HhGG
HhGg Hg
HHGg
HHgg
HhGg
Hhgg hG
HhGG
HhGg
hhGG
hhGg hg
HhGg
Hhgg
hhGg
hhgg

36. WHAT ARE THE PHENOTYPIC RATIO’S?
H h G g X H h G g
DD:
Dr:
rD:
rr: 9 3 1 HG Hg hG hg HG
HHGG
HHGg
HhGG
HhGg Hg
HHGg
HHgg
HhGg
Hhgg hG
HhGG
HhGg
hhGG
hhGg hg
HhGg
Hhgg
hhGg
hhgg

37. PROBABILITY Does real life follow Punnett Squares??
NO!!!!!! – only shows what will PROBABLY occur
Like flipping a coin 10 times:
PROBABILITY says you’ll get heads 50% of the time.
But you may not … try it.
Certainly over time, with hundreds and hundreds of flips, YES, you’ll end up with 50% heads 