1 genetics, the oldest branch of biology. 2 genetics = information flow transmission genetics =...
TRANSCRIPT
1
Genetics, the oldest branch of Biology
2
Genetics = Information Flow
Transmission Genetics = information flow between generations
Molecular Genetics = information flow within cells/organisms
DNA RNA Protein
3
pea plant from green seed
Data of Goss (1824)
Xpea plant from yellow seed
All seeds yellow – grow and self fertilize
Some pods with allyellow seeds – grow into plants andself fertilize
Some pods with all seedsyellow, some with green and yellow seeds
Some pods with allgreen seeds
Many pods with both yellow and green seeds
Self fertilization ofplants grown from green
All progeny plants Have pods with green seeds only
5
Data of Mendel (1866)
pea plant from green seed X
pea plant from yellow seed
All seeds yellow - Grow into plants and self fertilize(F1)First filial
generation
Count # of green and yellow seeds:-8023 total seeds-6022 yellow-2001 green – grown into plants: self fertilization yields all green seeds
(F2)second filialgeneration
Take 519 yellow seeds – grown into plants: self fertilizationOf these 519 plants, 166 bred true (all yellow seeds), 353 did not (mixed yellow and green seeds)
6
7
8
9
Mendel’s modelTrue breeding yellow AA
True breeding green aa
egg cells pollen cells
x
fertilize
Aa (yellow seeds) – grow into plants and self fertilizeF1
F2AA Aa
aA aa
(pollen)
(eggs)
A
A
a
a
3:1 yellow:green__________________¼ true breeding yellow½ “impure” yellow¼ true breeding green
aA
10
Mendel’s First Law
Each trait is governed by 2 particles*, one inherited from each parent. These two particles do not influence each other in any way within an individual, but separate, uncontaminated in any way, into gametes at the time of reproductive cellFormation. (an unstated corollary is that any pollen cell can fertilize any egg cell = random fertilization).
Testing the law:- the test cross (Aa x aa) predicts new ratios- other traits tested
*Introduce modern terms: dominant, recessive, alleles, phenotype, genotype, heterozygote,homozygote
11
12
Results of all Mendel's crosses in which parents differed for one character
Parental phenotype F1 F2 F2 ratio
1 . Round X wrinkled seeds All round 5474 round; 1850 wrinkled 2.96:1
2. Yellow X green seeds All yellow 6022 yellow; 2001 green 3.01:1
3. Purple X white petals All purple 705 purple; 224 white 3.15:1
4. Inflated X pinched pods All inflated 882 inflated; 299 pinched 2.95:1
5. Green X yellow pods All green 428 green; 152 yellow 2.82:1
6. Axial X terminal flowers All axial 651 axial; 207 terminal 3.14: 1
7. Long X short stems All long 787 long; 277 short 2.84: 1
What happens if two character traits are followed simultaneously?
13
Fig. 13.16
14
15
Mendel’s Second Law
Second Law=The Law of Independent Assortment:
During the formation of gametes, the segregation of alleles at one locus is independent of that of the segregation of alleles at any other.
16
Genes’ eye view of meiosis and mitosis
17
Mendel’s Second Law
The Law of Independent Assortment: During the formation of gametes, the segregation of alleles at one locus is independent of that of the segregation of alleles at any other.
Each trait is governed by 2 particles*, one inherited from each parent. These two particles do not influence each other in any way within an individual, but separate, uncontaminated in any way, into gametes at the time of reproductive cellFormation. (an unstated corollary is that any pollen cell can fertilize any egg cell = random fertilization).
Each trait is governed by 2 particles*, one inherited from each parent. These two particles do not influence each other in any way within an individual, but separate, uncontaminated in any way, into gametes at the time of reproductive cellFormation. (an unstated corollary is that any pollen cell can fertilize any egg cell = random fertilization).
Mendel’s First Law
A Gene's (allele) Eye View of Mitosis and Meiosis
18
Figure 10.5 Meiosis Accounts for the Segregation of Alleles
(Part 1)
19
Figure 10.5 Meiosis Accounts for the Segregation of Alleles
(Part 2)
20
Figure 10.8 Meiosis Accounts for Independent Assortment of
Alleles
A a
A aA a
A a
A a
mitotic metaphaseanaphase, telophase,cytokinesis
A
a
A
a
A
abb
BB
B
b
aa
bb
AA B
B
genotype: Aa; Bb
Meiosis I metaphase
Meiosis I product cells
replication
Meiosis I anaphase,telophase, cytokinesis
aa
bb
AA B
B
Meiosis I product cells
A B
A B
a b
a b
Meiosis II product cells
Meiosis II anaphase,telophase, cytokinesis
Meiosis II metaphase
Meiosis II metaphase
AB
AB
ab
ab
aa
bb
AA
BB
Meiosis I product cells
A
B
A
a
a
b
Meiosis II products cells
Meiosis II anaphase,telophase, cytokinesis
Meiosis II metaphase
Meiosis II metaphase
bAb
Ab
aB
aB B
25
Eye Color Is a Sex-Linked Trait in Drosophila
26
27
28
Probability – Predicting Results
Rule of addition: the probability of 2 mutually exclusive events occurring simultaneously is the sum of their individual probabilities.
When crossing Pp x Pp, the probability of producing Pp offspring is probability of obtaining Pp (1/4), PLUSprobability of obtaining pP (1/4)¼ + ¼ = ½
29
Probability – Predicting Results
Rule of multiplication: the probability of 2 independent events occurring simultaneously is the PRODUCT of their individual probabilities.
When crossing Rr Yy x RrYy, the probability of obtaining rr yy offspring is:probability of obtaiing rr = ¼probability of obtaining yy = ¼probability of rr yy = ¼ x ¼ = 1/16
30
Testcross
Testcross: a cross used to determine the genotype of an individual with dominant phenotype
-cross the individual with unknown genotype (e.g. P_) with a homozygous recessive (pp)
-the phenotypic ratios among offspring are different, depending on the genotype of the unknown parent
31
32
33
Genes GenesPhenotypes
polygenic inheritancepleiotropy
34
35
Figure 10.12 Inheritance of Coat Color in Rabbits “continuous” variation: multiple alleles of one gene
36
Gene Interaction (alleles of same gene)- dominance- incomplete dominance- co-dominance- lethal alleles
Gene Interaction (alleles of different genes):- in different pathways
(Drosophila eye pigmentation)- in same pathway
- recessive epistasis
37
Fig. 13.18
38
codominance
39
40
Fig. 13.20
41
wild-type (+/+)
Antennapedia mutant
(Antp/+)
fly heads
+/+ x Antp/+
½ “Antp” (Antp/+)½ “+” (+/+)
Antp/+ x Antp/+
2/3 “Antp” (Antp/+)1/3 “+” (+/+)
?¼ +/+ (“+”)½ Antp/+ (“Antp”)¼ Antp/Antp (lethal)
43
Fig. 13.19
44
Extensions to Mendel
45
Eye Color Is a Sex-Linked Trait in Drosophila
46
white-eyed, normal-winged female x red-eyed, miniature winged male (wild type)
w+ mw m+
w m+
w m+
w+ m
wild type females w m+
white-eyed, normal-winged males
x
w m+
½ red-eyed, miniature winged
for male progeny, EXPECT:
w+ m
½ white-eyed, normal-winged
64% of males fell into above classes, but 36% were either wild typeOr doubly mutant !!!!!!!
47
w m+
w+ m
wild type females
genetic recombination = chromosomal crossing over
36% of chromosomes in meiosis I:
w m+
white-eyed, normal-winged males
x
w+ m+ w m
36% of males are either doubly mutant or wild type :
48
Chiasmata visible inLocusta migratoria spermatogenesis
A synaptonemal complex
49
50
51
52
53
54
Genetic Mapping
Mapping genes in humans involves determining the recombination frequency between a gene and an anonymous marker
Anonymous markers such as single nucleotide polymorphisms (SNPs) can be detected by molecular techniques.
55
Testis Determining Factor (SRY)
Channel Flipping (FLP)
Catching and Throwing (BLZ-1)
Self Confidence (BLZ-2) - (note: unlinked to ability)
Addiction to Death and Destruction Films (T2)
Preadolescent fascination with Arachinida and Reptilia (MOM-4U)
Sitting on John Reading (SIT)
Selective Hearing Loss (HUH?)
Lack of Recall for Important Dates (OOPS)
Inability to Express Affection Over the Phone (ME-2)
Spitting (P2E)
New Genes Identified on the Human Y Chromosome
57
• effects of recombination on chromosomes within a family
• siblings inherit different chromosome regions from their parents
• grandson inheritschromosome regions
from all four of hisgrandparents’chromosomes
58
59
Early Ideas of Heredity
Before the 20th century, 2 concepts were the basis for ideas about heredity:
-heredity occurs within species
-traits are transmitted directly from parent to offspring
This led to the belief that inheritance is a matter of blending traits from the parents.
60
Early Ideas of Heredity
Botanists in the 18th and 19th centuries produced hybrid plants.
When the hybrids were crossed with each other, some of the offspring resembled the original strains, rather than the hybrid strains.
This evidence contradicted the idea that traits are directly passed from parent to offspring.
61
Early Ideas of Heredity
Gregor Mendel
-chose to study pea plants because:
1. other research showed that pea hybrids could be produced
2. many pea varieties were available
3. peas are small plants and easy to grow
4. peas can self-fertilize or be cross-fertilized
62
Early Ideas of Heredity
Mendel’s experimental method:1. produce true-breeding strains for each
trait he was studying2. cross-fertilize true-breeding strains having
alternate forms of a trait -perform reciprocal crosses as well
3. allow the hybrid offspring to self-fertilize and count the number of offspring showing each form of the trait
63
Monohybrid Crosses
Monohybrid cross: a cross to study only 2 variations of a single trait
Mendel produced true-breeding pea strains for 7 different traits
-each trait had 2 alternate forms (variations)
-Mendel cross-fertilized the 2 true-breeding strains for each trait
64
Monohybrid Crosses
F1 generation (1st filial generation): offspring produced by crossing 2 true-breeding strains
For every trait Mendel studied, all F1 plants resembled only 1 parent
-no plants with characteristics intermediate between the 2 parents were produced
65
Monohybrid Crosses
F1 generation: offspring resulting from a cross of true-breeding parents
F2 generation: offspring resulting from the self-fertilization of F1 plants
dominant: the form of each trait expressed in the F1 plants
recessive: the form of the trait not seen in the F1 plants
66
Monohybrid Crosses
F2 plants exhibited both forms of the trait in a very specific pattern:¾ plants with the dominant form¼ plant with the recessive form
The dominant to recessive ratio was 3 : 1.Mendel discovered the ratio is actually:
1 true-breeding dominant plant2 not-true-breeding dominant plants1 true-breeding recessive plant
67
Monohybrid Crosses
gene: information for a trait passed from parent to offspring
alleles: alternate forms of a gene
homozygous: having 2 of the same allele
heterozygous: having 2 different alleles
68
Monohybrid Crosses
genotype: total set of alleles of an individual
PP = homozygous dominant
Pp = heterozygous
pp = homozygous recessive
phenotype: outward appearance of an individual
69
Monohybrid Crosses
Principle of Segregation
Two alleles for a gene segregate during gamete formation and are rejoined at random, one from each parent, during fertilization.
70
Monohybrid Crosses
Some human traits are controlled by a single gene.-some of these exhibit dominant inheritance-some of these exhibit recessive inheritance
Pedigree analysis is used to track inheritance patterns in families.
71
Dihybrid Crosses
Dihybrid cross: examination of 2 separate traits in a single cross
-for example: RR YY x rryy
The F1 generation of a dihybrid cross (RrYy) shows only the dominant phenotypes for each trait.
72
Dihybrid Crosses
The F2 generation is produced by crossing members of the F1 generation with each other or allowing self-fertilization of the F1.
-for example RrYy x RrYy
The F2 generation shows all four possible phenotypes in a set ratio:
9 : 3 : 3 : 1
73
Dihybrid Crosses
Principle of Independent Assortment
In a dihybrid cross, the alleles of each gene assort independently.
74
Extensions to Mendel
Mendel’s model of inheritance assumes that:
-each trait is controlled by a single gene
-each gene has only 2 alleles
-there is a clear dominant-recessive relationship between the alleles
Most genes do not meet these criteria.
75
Extensions to Mendel
Polygenic inheritance occurs when multiple genes are involved in controlling the phenotype of a trait.
The phenotype is an accumulation of contributions by multiple genes.
These traits show continuous variation and are referred to as quantitative traits.
For example – human height
76
Extensions to Mendel
Pleiotropy refers to an allele which has more than one effect on the phenotype.
This can be seen in human diseases such as cystic fibrosis or sickle cell anemia.
In these diseases, multiple symptoms can be traced back to one defective allele.
77
Extensions to Mendel
Incomplete dominance: the heterozygote is intermediate in phenotype between the 2 homozygotes.
Codominance: the heterozygote shows some aspect of the phenotypes of both homozygotes.
78
Extensions to Mendel
The human ABO blood group system demonstrates:
-multiple alleles: there are 3 alleles of the I gene (IA, IB, and i)
-codominance: IA and IB are dominant to i but codominant to each other
79
Extensions to Mendel
The expression of some genes can be influenced by the environment.
for example: coat color in Himalayan rabbits and Siamese cats
-an allele produces an enzyme that allows pigment production only at temperatures below 30oC
80
Extensions to Mendel
The products of some genes interact with each other and influence the phenotype of the individual.
Epistasis: one gene can interfere with the expression of another gene