Wednesday 4/9/14

1
Wednesday 4/9/14

• AIM Why is Gregor Mendel the father of genetics?
• DO NOW How many chromosomes do you have and
  where do they come from?
• What would happen if you had an extra chromosome
  and why?
• HOMEWORK Text read pages 267-70. Reading check
  pages 267 and 268, q 1 and 2 pages 270

2
What is genetics?
3
Genetics

• The study of inherited traits
• Chromosomes are the units of inheritance
• Chromosomes carry genes
• Genes are the specific direction or code for your
  physical trait
• Genes code for proteins
• Proteins cause chemical reactions
• Chemical reactions lead to physical traits

4
Where do your inherited traits come from?

• Your dads sperm and your moms egg

5
(No Transcript)
6
Homologous chromosome

• Similar in size shape and genetic content
• Homologous chromosomes pair up at fertilization
• nn2n

7
(No Transcript)
8
Remember

• Zygote gets one complete set of chromosomes from
  the egg
• And one complete set of chromosomes from the
  sperm
• Bringing together homologous chromosomes

9
Haploid haploid diploid
10
Human Chromosomes

• Total we have 23 pairs
• 2(23)46
• 22 of those pairs are called autosomes
• The 23 pair is the sex chromosomes

11
Sex Chromosomes

• XX female
• XY male

12
Y chromsome

• Carries the SRY gene
• SRY sex determining region
• If the SRY gene is turned on, then gonads develop
  into testis and fetus becomes male
• If not then gonads become ovaries

13

• AIM How does the structure of DNA relate to its
  function?
• DO NOW How many chromosomes do each of your
  cells have?
• How many genes does each of your cells have?
• How many nuclei does each of your cells have?
• Homework text read pages 293,296,297 and 299.
  Answer Reading questions 293,296,297

14

• Somatic or body cells have 46 chromosomes
• Examples of somatic cells
• Cardiac cells lung cells brain cells
• Skin cells muscle cells gall bladder cells
• Tracheal cells esophagal cells liver cells
• Gametes or sex cells have 23 chromosomes
• Male-sperm
• Female-ova or egg
• There are thousands of genes in each cell
• There is one nucleus in each cell that houses the
  chromosomes which carry genes on them
• Each cell expresses specific genes to make them
  specialized

15
So how do we know anything about genetics and
homologous chromosomes?
16
Gregor Mendel

• Father of genetics
• Looked at the pea plant
• Specifically 7 visible traits
• Followed their inheritance over many generations
• HE KNEW NOTHING ABOUT GENES!!!!!

17
(No Transcript)
18
Mendel was lucky

• Each of the 7 traits Mendel observed was only
  present in 1 of 2 possible forms
• Ex Plant color was either purple or white
• Pea shape was either round or wrinkled
• Mendel used this when performing his experiments.

19
Thursday 4/10/14

• AIM How did Gregor Mendel develop his basic laws
  of heredity?
• DO NOW What is genetics? How do we know
  anything about genetics?
• HOMEWORK Textbook read pages 276-277. do the
  reading check on page 277

20
Genetics

• The study of inherited traits
• Chromosomes are the units of inheritance
• Chromosomes carry genes
• Genes are the specific direction or code for your
  physical trait
• Genes code for proteins
• Proteins cause chemical reactions
• Chemical reactions lead to physical traits

21

• AIM How did Mendel develop his basic laws of
  heredity?
• DO NOW What is the difference between self
  fertilization and cross fertilization?
• HOMEWORK textbook read pages 267-270. 1-Explain
  the difference between true breeding and hybrid.
• 2- Define P generation, first filial generation
  and second filial generation.
• 3- Explain why Mendel studied pea plants

22
Gregor Mendels experiments Fertilization

• Self-fertilization egg in the flower is
  fertilized by the sperm of the same flower
• Cross-fertilization sperm from a foreign plant
  fertilizes an egg

23
Gregor Mendel

• Used both the processes of self fertilization and
  cross fertilization to experiment on pea plants
• This helped him develop his basic laws of heredity

24
Definitions

• True breed or pure breed plants with a trait
  such as purple flowers that is always inherited
  by all offspring
• Can only produce one type of gamete
• HYBRID
• The offspring of a cross fertilization
• 2 parents similar to sexual reproduction
• Can produce different types of gametes

25
Definitions continued

• Monohybrid cross tracks one trait at a time
• Ex flower color
• Dihybrid cross

26
Mendels work

• Self fertilized true breed parents for many
  generations
• All offspring gave the same results
• Cross fertilized true breeds to get an F1
  generation
• Self fertilized the F1 and observed the F2
  generation

27

28
Mendels Experiment

• Parent Generation (P1)
• Purple true breed X White true breed
• First Filial (F1)
• 100 Purple flowers Self fertilize
• Second Filial (F2)
• 75 Purple 25 White
• 31 ratio

29
Why were all the F1 generation flowers purple?

• Purple Trait is obviously dominant over the white
  trait
• The white trait was hidden but not gone

30
Why were some of the F2 generation part purple
and part white?

• The F1 parent was carrying the white trait but it
  was masked or hidden.
• White is recessive to purple

31
Just from looking at these results, what can
Mendel conclude?
32
Mendels Conclusions from a monohybrid cross

• 1- Copies of inherited traits must be separated
  when gametes are formed
• 2- When present in 2 forms one form is dominant
  over the other
• 3- the recessive trait will show itself when
  present in two copies

33
Tuesday 4/22/14
34
From these experiments, Mendel concluded

• Traits are determined by physical unit that come
  in pairs (he did not know these would later be
  called alleles)
• Gametes separate and carry only 1 allele(copy)
  for each gene
• The particular allele that ends up in a gamete is
  caused by chance
• One allele is dominant and one recessive
• True-breeding organisms have the 2 copies of the
  same allele (homozygous)

35

• AIM How can we predict the possible genotypes
  and phenotypes of offspring?
• DO NOW 2- if I cross fertilized a true breed
  green seed pea plant by a true breed yellow seed
  pea plant, what phenotypes do I expect to get?
• HOMEWORK Textbook read pages 272-273. answer
  questions 1,2,3 on page 275

36
Create a list

• 7 traits observed by Gregor Mendel
• 1- Flower color
• 2- Plant size
• 3- Flower position
• 4-Seed color
• 5- shape of pod
• 6- Pod color
• 7- Seed shape
• Each of these traits has a dominant and a
  recessive phenotype

37

38
Seed color

• Dominant phenotype green
• Recessive phenotype yellow
• Genotype Phenotype
• GG
• Gg
• gg

39
Mendel had no idea about the following

• We know we get 2 copies of genes
• 1 from sperm
• 1 from egg
• Allele is a copy of a gene
• Homologous chromosomes carry alleles

40
(No Transcript)
41
Monohybrid Cross

• Tracked one (mono) trait at a time

42
Mendels work

• Cross fertilized two true breed parents that
  displayed opposite traits.(P or Parental
  generation)
• All First filial or F1 offspring were purple

43
What happened to the white color?
44
Self-fertilized F1

• Second filial or F2 generation yielded about ¼
  white and ¾ purple
• So the white flower color was not lost just masked

45
Self-fertilized F2

• Saw that all white flowered F2 yielded all white
  F3 but the purple still yielded 31 ratio of
  purple to white
• Therefore the white allele was not lost but
  rather hidden or masked by the purple allele

46
From these experiments, Mendel concluded

• Traits are determined by physical unit that come
  in pairs (he did not know these would later be
  called alleles)
• Gametes separate and carry only 1 allele for each
  gene
• The particular allele that ends up in a gamete is
  caused by chance
• One allele is dominant and one recessive
• True-breeding organisms have the 2 copies of the
  same allele

47
Thursday 4/24/14

• AIM why did Mendel decide to perform a dihybrid
  cross?
• DO NOW Let A represent the allele coding for
  terminal flowers and a axial flowers. Complete
  the following table
• HOMEWORK text read pages 274-275. answer
  questions 3 and 4 page 275

Genotype Phenotype
AA Homozygous dominant terminal
Aa Heterogygous terminal
aa Homozygous recessive axial
48
Mendels Law of dominance

• When two different alleles are present, the
  dominant alleles gives the resulting phenotype
  and masks the trait of the recessive allele
• However the recessive allele is still present
• Homozygous Dominant and heterozygous organisms
  display the same phenotype
• Recessive alleles are only displayed when present
  in 2 copies
• Homozygous recessive

49
Mendels Law of segregation

• Pairs of alleles on homologous chromosomes
  separate from each other during gamete formation
• Gametes receive only one allele from a homologous
  pair.
• Fertilization produces offspring with a copy of
  one allele from mom and one from dad

50

51

52

53
Mendels Hypothesis were consistent with his
results

• 2 plants that look alike may actually carry
  different combinations of alleles
• Genotype the combination of alleles carried by
  an organism
• Homozygous Dominant AA
• Heterozygous Aa
• Homozygous recessive aa
• Phenotype The physically observable feature
• So a homozygous dominant individual and a
  heterozygous individual will display the same
  phenotype but have different genotypes
• The only way for the recessive phenotype is
  observed is if the individual is homozygous
  recessive

54
Mendel was not satisfied

• He wanted to see if alleles could be inherited
  together
• He asked himself are all round seeds yellow?
• Are all green seeds wrinkled?
• He looked at two traits at the same time
• Dihybrid cross
• Ex seed shape and seed color
• His results were inconclusive which means all
  round seeds were not yellow all wrinkled seeds
  were not green

55
In order to investigate, Mendel performed a
dihybrid cross

• Dihybrid cross crossed plants that differed in
  more than one trait
• Specifically Mendel looked at seed shape and seed
  color

56
Cross Fertilization
Homozygous Dominant
Homozygous recessive
ALL heterozygous
Dominant shape Recessive color
Dominant color Recessive shape
Both Dominant traits
Both recessive traits
57

• R-round
• r-wrinkled
• Y-Yellow
• y-green

58

59
Friday 4/25/14
60
Mendels dihybrid cross

• P true breed RRYY(Round Yellow) x rryy(wrinkled
  green)
• All F1 RrYy (Round Yellow)
• Allowed F1 to self-fertilize which yielded the
  following phenotypic ratio
• F2 9331 ratio of
• Round Yellow Round green wr Yellow wr,green

61

• F1 Self Fertilization

62

F1 self fertilization
63

64

Display of all possible genotypes
65

66

67

68

69

70
Law of independent assortment

• Multiple traits are inherited independently of
  each other because alleles of genes are
  distributed independently during gamete formation
• Genes found on different chromosomes assort
  independently of each other during gamete
  formation
• Genes are inherited independently

71
What was the major question Mendel was trying to
answer when he performed his dihybrid cross?

• Mendel asked himself if two characteristics were
  inherited together.
• Specifically is seed color inherited with seed
  shape?

72
Testcross

• Cross fertilize a dominant phenotype plant with a
  homozygote recessive plant
• WHY?
• Purpose is to analyze the ratio of the offspring
• This will tell us the parents genotype
• (homozygous dominant or heterozygous)

73
What do we call this type of cross ad why would
we perform it?
74
Test cross

• Determines the genotype of a dominant displayed
  phenotype

75
Testcross

• The only way to display the recessive phenotype
  is to have a homozygous recessive genotype
• After performing a testcross, If the f1 offspring
  display ALL dominant phenotypes then I know the
  Parent genotype is homozygous Dominant.
• If the offspring display 50 dominant phenotype
  and 50 recessive than the Parental genotype is
  heterozygous

76
(No Transcript)
77
(No Transcript)