1. Introduction to Genetics
Honors Biology

2. Review of Reproduction
2 Kinds of Reproduction
Asexual – One parent, offspring look same as parent, “clone”
Mechanism – Cells go from 2n to 2n
Kinds: fragmentation, budding, mitosis, fission, runners
Pros:
Organisms look the same
No need to find mate
If it works, don’t change it!
Cons:
No genetic diversity!
Honors Biology

3. Reproduction Review Cont’d
Sexual – 2 parents, union of egg and sperm, melding of traits
Examples:
Earthworms – hermaphroditic
Squid
Bower birds
Falcons
Honors Biology

4. *** This is how you make egg and sperm!!
Sexual Reproduction
Meiosis
2n n
Diploid Haploid
(Normal # of chromosomes) (1/2 no. of chromosomes)
*** This is how you make egg and sperm!!
Honors Biology

5. Sexual Reproduction in Humans
Chromosome Number? 46
Meiosis
Egg Sperm
Fertilization
Honors Biology

6. Chromosome Review 46 chromosomes arranged in homologous pairs
Exception?
1 from mom & 1 from dad = 23 pairs
Another pair. Have same genes, but different genes from the first pair!
Weight
Eye color
Insulin
Homologous Pair = 2 chromosomes with same genes
Lips
Height
Hair Color 1 2 3 4
Honors Biology

7. Chromosome Review Cont’d
Chromosome = DNA Ladder and protein
(chromatin)
It is the nucleotide sequence within the gene that dictates what proteins (traits) will be expressed (shown) in the organism.
Gene = the area on chromosome that codes for a product
Honors Biology

8. Gregor Mendel Known as “the father of genetics”
Educated at monastery and studied at University
Was put in charge of the abbey garden
Documented inheritance
patterns in garden peas
Honors Biology

9. Mendel chose peas wisely
Easy to see & study traits
flower color, seed color, seed shape, etc.
Strict control over which plants mated with which
self-fertilize
cross-pollinate
Many generations can be grown in a
short time
Lots of offspring per cross
Honors Biology

10. Mendel’s work Bred pea plants P F1 F2
Pollen transferred from white flower to stigma of purple flower
Bred pea plants
cross-pollinate true breeding parents (P)
P = parental
raised seed & then observed traits (F1)
F = filial
allowed offspring to self-pollinate & observed next generation (F2) P
anthers
removed
all purple flowers result F1
P = parents
F = filial generation
self-pollinate F2
Honors Biology

11. Looking closer at Mendel’s workP
generation
true-breeding
purple-flower peas X
true-breeding
white-flower peas
100% F1
generation
(hybrids)
purple-flower peas
In a typical breeding experiment, Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties.
The true-breeding parents are the P generation and their hybrid offspring are the F1 generation.
Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 generation.
self-pollinate F2
generation
3:1
75%
purple-flower peas
25%
white-flower peas
Honors Biology

12. Traits are inherited as discrete units
For each characteristic, an organism inherits 2 alleles, 1 from each parent
diploid organism
inherits 2 sets of chromosomes, 1 from each parent
homologous chromosomes
like having 2 editions of encyclopedia
Encyclopedia Britannica
Encyclopedia Americana
What are the advantages of being diploid?
Honors Biology

13. What did Mendel’s findings mean?
Realized that genes come in alternative “versions”
purple vs. white flower color
Alleles - different versions of a gene
different alleles vary in the sequence of nucleotides at the specific locus of a gene
some difference in sequence of A, T, C, G
purple-flower allele & white-flower allele are two DNA variations at flower-color locus
Honors Biology

14. What did Mendel’s findings mean?
Some traits mask others
purple & white flower colors are
separate traits that do not blend
purple x white ≠ light purple
purple hides white
dominant allele
Expressed form of the trait
Dominant letter
masks other alleles
recessive allele
Trait that is not expressed, if
dominant form is present
Lowercase letter
I’ll speak for both of us!
Recessive allele
Dominant allele
homologous chromosomes
Honors Biology

15. Mendel collected data for 7 pea traits
Honors Biology

16. Genotype vs. phenotype
Difference between how an organism “looks” & its genetics
phenotype
description of an organism’s trait
genotype
description of an organism’s genetic makeup F1 P X
purple
white
all purple
Explain Mendel’s results using
…dominant & recessive
…phenotype & genotype
Honors Biology

17. PP pp Pp Making crosses x Can represent alleles as letters
flower color alleles  P or p
true-breeding purple-flower peas  PP
true-breeding white-flower peas  pp F1 P X
purple
white
all purple PP x pp Pp
Honors Biology

18. Looking closer at Mendel’s workX
phenotype P
true-breeding
purple-flower peas
true-breeding
white-flower peas PP pp
genotype
100% F1
generation
(hybrids)
purple-flower peas
In a typical breeding experiment, Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties.
The true-breeding parents are the P generation and their hybrid offspring are the F1 generation.
Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 generation. Pp Pp Pp Pp
self-pollination
3:1
75%
purple-flower peas
25%
white-flower peas F2
generation ? ? ? ?
Honors Biology

19. phenotype & genotype can have different ratios!
Aaaaah,
phenotype & genotype can have different ratios!
Punnett squares F1
generation
(hybrids)
Pp x Pp %
genotype %
phenotype P p
male / sperm PP
25%
75% Pp
50% P p
female / eggs PP Pp Pp Pp pp
25%
25% pp
1:2:1
3:1
Honors Biology

20. Genotypes Homozygous = same alleles = PP, pp
Heterozygous = different alleles = Pp
homozygous dominant
heterozygous
homozygous recessive
Honors Biology

21. Can’t tell by lookin’ at ya!
Phenotype vs. genotype
2 organisms can have the same phenotype but have different genotypes
homozygous dominant PP
purple Pp
heterozygous
purple
Can’t tell by lookin’ at ya!
How do you determine the genotype of an individual with with a dominant phenotype?
Honors Biology

22. Test cross
Breed the dominant phenotype — the unknown genotype — with a homozygous recessive (pp) to determine the identity of the unknown allele x
How does that work?
is it PP or Pp? pp
Honors Biology

23. How does a Test cross work?x x pp PP Pp pp p p p p P P Pp Pp Pp Pp P p Pp Pp pp pp
100% purple
50% purple:50% white or 1:1
Honors Biology

24. Mendel’s 1st law of heredityPP P
Law of Segregation
during meiosis, pairs of alleles
segregate (separate)
homologous chromosomes separate
each allele is packaged into a separate gamete
New pairs come together at fertilization pp p Pp P p
Honors Biology

25. Whoa! And Mendel didn’t even know DNA or genes existed!
Law of Segregation
Which stage of meiosis creates the law of segregation?
Metaphase 1
Whoa! And Mendel didn’t even know DNA or genes existed!
Honors Biology

26. Monohybrid Cross Monohybrid Cross – A cross that looks at one trait.
Two parents with brown eyes have a child with blue eyes. How can this be?
B_____ x B_____ = bb (blue eyes)
Honors Biology

27. Example 1
Tall is dominant to short in pea plants. Cross a heterozygous tall plant with a short plant. What are the genotype and phenotype ratios? X
Honors Biology

28. Solution 1st – Figure out your letters 2nd – Figure out your parents
Tall = T
short = t
2nd – Figure out your parents
Heterozygous Tall = Tt
White – tt
3rd – Figure out your cross
Tt x tt
4th – Draw your Punnett Square
Honors Biology

29. Solution Cont’d T t Tt tt Tt x tt
Phenotype: 2 Tall and 2 short, or 1:1
Genotype: 2 Tt and 2 tt, or 1:1 T t Tt tt
Honors Biology

30. Probability
Mendel used the laws of probability to predict and explain the results of his experiments.
Probability – The expected frequency of a particular event that will occur when the even is repeated an infinite number of items.
Prob. = # of occurrences of a targeted event
total # of occurrences
Honors Biology

31. Probability Examples Prob. = # of occurrences of a targeted event
total # of occurrences
What is the probability of rolling a dice and getting a 3?
The probability of pulling the Ace of Spades out of a deck of cards?
The probability of pulling any card other than the Ace of spades?
The probability that a coin you toss will be heads?
1/6
1/52
51/52
1/2
Honors Biology

32. Genetics & Probability
Mendel’s experiments
reflect the same laws of probability that apply to tossing coins or rolling dice
Honors Biology

33. Probability & geneticsBB B
Calculating probability of making a specific gamete is just like calculating the probability in flipping a coin
probability of tossing heads?
probability making a B gamete?
100% Bb B b
50%
Honors Biology

34. Probability & genetics
Outcome of 1 toss has no impact on the outcome of the next toss
probability of tossing heads each time?
probability making a B gamete each time?
50% Bb B b
50%
Honors Biology

35. Calculating probability
sperm
egg
offspring
Pp x Pp P PP
1/2 x
1/2 =
1/4 P p
male / sperm P p Pp
1/2 x
1/2 =
1/4 P p
female / eggs p P + PP Pp
1/2 x
1/2 =
1/4
1/2 Pp pp p pp
1/2 x
1/2 =
1/4
Honors Biology

36. Rule of multiplication
Multiplication-Used when you need to find the probability of two or more independent events.
probability that 2 coins tossed at the same time will land heads up
probability of Pp x Pp  pp
1/2 x 1/2 = 1/4 Pp P p
1/2 x 1/2 = 1/4
Honors Biology

37. Rule of addition
Chance that an event can occur 2 or more different ways
sum of the separate probabilities
probability of Bb x Bb  Bb
sperm
egg
offspring B b Bb
1/4 +
1/2
1/2 = x
1/4 b B Bb
1/2 = x
1/4
Honors Biology

38. Probability Myths
Statistical Nature of Inheritance – a couple will NOT automatically have 2 boys and 2 girls if they have 4 children.
HOWEVER, with probability, the larger the sample size the closer the results will be to the predicted ratios.
Honors Biology

39. Practice
Tall is dominant to short in pea plants. Cross two heterozygous tall plants. What are the genotypes and phenotypes?
Round seeds are dominant to wrinkled seeds in pea plants. Cross a homozygous round with a heterozygous round. What are the genotypes and phenotypes?
Brown eyes are dominant to blue eyes. Cross a heterozygous brown-eyed person with a homozygous brown-eyed person. What are the phenotypes and genotypes?
Honors Biology

40. For your Quiz Next Class
Know your key terms!
Homologous chromosomes, allele, genotype, phenotype, dominant, recessive, heterozygous, homozygous, monohybrid cross
Know how to do simple monohybrid cross problems.
Honors Biology

41. 1st Period Movies http://youtu.be/QRWWReUUFN8 
Leya, July, Helaina: .mov file
Honors Biology

42. 3rd Period Movies http://www.youtube.com/watch?v=-YihajpMGCc
Chloe, Grace, Elsa, Kate: .mov file
Patrick, Josh, Jawan, and August: . mov file
Vonnie, Kiran, Lyle, and Brooke: .mov file
Honors Biology

43. 4th Period Movies http://youtu.be/rJxqueYZdX8
Aidan, Aidan, Zoe, and Ben R.: .mov file
Honors Biology