CHAPTER 11 Introduction to Genetics
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Transcript of CHAPTER 11 Introduction to Genetics
CHAPTER 11Introduction to Genetics
Genetics- the scientific study of heredity
Gregor Mendel
Gregor Mendel’s work
Fertilization- sexual reproduction, union of male and female reproductive cells
True-breeding- to produce offspring that are identical to the parents in characteristics
Gregor Mendel’s work
Cross-pollination- taking the sperm cells from one plant and joining them with the egg cells of another plant
Gregor Mendel’s work
Trait- specific characteristic
P generation- Parental generation
F1 generation- offspring of first generation
F1 “first filial”
Hybrids- offspring of
parents with different traits
Conclusions
1. Biological inheritance is determined by factors that are passed from one generation to the next
Genes- chemical factors that determine traits
ex: the gene for plant height
Alleles- different forms of a gene
ex: the short allele and the tall allele
Conclusions
2. Principle of dominance
some alleles are dominant and some are recessive
Segregation
What happened to the traits of the P generation that disappeared in the F1 generation?
Segregation
F2 generation- the F1
generation self-pollinated
Segregation
The gametes (sex cells)
contain only one of the traits.
The gametes separate the
traits and recombine them
in the offspring
11-2 Probability and Punnett Squares
• Probability- the likelihood that a particular event will occur
Punnett Squares
• Can be used to predict and compare the genetic variations that will result from a cross
• Homozygous- two identical alleles for a particular trait. Ex: TT or tt
• Heterozygous- two different alleles for a particular trait. Ex: Tt
• Phenotype- physical characteristics• Tall plants or short plants
• Genotype- genetic makeup• TT, tt, or Tt
• Can two organisms have the same phenotype but a different genotype?
Probabilities predict averages
• Increasing the number of offspring yields results closer to the predicted averages
11-3 Exploring Mendelian Genetics
• Independent Assortment• Does the segregation of one pair of alleles affect
the segregation of another pair of alleles?
• Round Yellow X Wrinkled Green
Round Yellow X Wrinkled Green• All the F1 generation were round yellow
• Which traits are dominant?
ry ry ry ryRY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
F2 generation, RrYy X RrYy
RY Ry rY ryRY
Ry
rY
ry
F2 generation, RrYy X RrYy
RY Ry rY ryRY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryy
F2 generation, RrYy X RrYy
• Round Yellow
RY Ry rY ryRY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryy
F2 generation, RrYy X RrYy
• Round Yellow• Round Green
RY Ry rY ryRY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryy
F2 generation, RrYy X RrYy
• Round Yellow Wrinkled Yellow• Round Green
RY Ry rY ryRY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryy
F2 generation, RrYy X RrYy
• Round Yellow Wrinkled Yellow• Round Green Wrinkled Green
RY Ry rY ryRY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryy
9: 3: 3: 1 Ratio
• Round Yellow Wrinkled Yellow• Round Green Wrinkled Green
RY Ry rY ryRY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryy
Independent Assortment
• Genes for different traits can segregate independently during the formation of gametes.
RY Ry rY ryRY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy RryyrY RrYY RrYy rrYY rrYyry RrYy Rryy rrYy rryy
Beyond Dominant and Recessive Alleles
• Incomplete Dominance
R RWW
Beyond Dominant and Recessive Alleles
• Incomplete Dominance – neither allele is dominant
R RW RW RWW RW RW
Beyond Dominant and Recessive Alleles
• Incomplete Dominance – neither allele is dominant
R WRW
Beyond Dominant and Recessive Alleles
• Incomplete Dominance – neither allele is dominant
R WR RR RWW RW WW
Beyond Dominant and Recessive Alleles
• Codominance- both alleles contribute to the phenotype
• Ex: Brown mated with white creates a mixture of brown and white (roan)
Beyond Dominant and Recessive Alleles
• Multiple Alleles- genes that have more than two alleles
• Ex: Human blood types• Blood phenotypes: A, B, AB, O
Phenotype Genotype Genotype
Type A IA IA IA i
Type B IB IB IB i
Type AB IA IB
Type O i i
• Polygenic Traits- Phenotype is controlled by many different genes
• Ex: Skin color is controlled by at least three different genes
Thomas Hunt Morgan• Fruit Flies (Drosophila melanogaster)
• Ideal for genetics experiments:• Reproduce quickly
• Large # of offspring
• Small in size
Nature vs. Nurture
• Which has a greater influence on an organism, the DNA or the environment?
Nature vs. Nurture
Phenotype often depends on genes and the environment.
• Humans:
• Height- nutrition
• Strength- exercise
• Skin color- exposure to sunlight
• Intelligence- experience
11-4 Meiosis
Chromosome Number
Fruit Fly has 8 chromosomes
4 from father
4 from mother
Homologous chromosomes- same type of chromosome
The 4 chromosomes from the male parent are homologous to the 4 chromosomes from the female parent.
Diploid vs. Haploid
• Diploid- a cell that contains two sets of homologous chromosomes. 2N• Fruit flies: 2N= 8 Humans: 2N=46
Most adult cells are diploid.
Haploid- a cell that contains one set of chromosomes. N
Fruit flies: N= 4 Humans: N=23
Gametes (sex cell: sperm, egg) are haploid.
Phases of Meiosis
• Meiosis- the process of the number of chromosomes per cell is cut in half in the production of daughter cells by the separation of homologous chromosomes
Interphase Prophase Metaphase Anaphase Telophase Cytokinesis
Phases of Meiosis
Interphase I Prophase I Metaphase I Anaphase I Telophase I Cytokinesis
Prophase II Metaphase II Anaphase II Telophase II Cytokinesis
Phases of Meiosis
Interphase I Prophase I Metaphase I Anaphase I Telophase I Cytokinesis
Prophase II Metaphase II Anaphase II Telophase II Cytokinesis
4N2N2N
2N
2N
2N
NN
NN
Phases of Meiosis
Interphase I Prophase I Metaphase I Anaphase I Telophase I Cytokinesis
Prophase II Metaphase II Anaphase II Telophase II Cytokinesis
4N2N2N
2N
2N
2N
NN
NN
Phases of Meiosis
Interphase I Prophase I Metaphase I Anaphase I Telophase I Cytokinesis
4N2N2N
2N
• Tetrad- a structure of two homologous chromosomes, 4 sister chromatids
• Occurs during Prophase I• Crossing over- process of exchanging portions of
sister chromatids
• Crossing over creates many unique combinations of gamete cells.
Sperm production
4N2N2N
2N
NN
NN
Egg production
4N2N2N
2N
NN
NN
Polar Body
Polar Body
Polar Body
Zygote Formation
• Egg and Sperm join together to form a zygote• Egg= N
• Sperm= N
• Zygote = 2N
11-5 Linkage and Gene Maps
T T TT TT
T T
T T
TTTT
T t TT t t
T t
T t
tTt
T
T Tt Tt Ttt Tt Tt
T T TT TT
T T
T T
TTT
T
t t t t t t
t t
t t
ttt
t
T tT TT Ttt Tt tt
T t T t T t
T t
T t
tTt
T
T t T t T t
T t
T t
tTt
T
It is really the chromosomes that get sorted not the individual genes in meiosis
tT
tT tT
tT tT
What if there are two trait on one chromosome?
What if there are two trait on one chromosome?
Those traits would be inherited together.
For fruit flies, body color and wing size are linked. Those genes are on the same chromosome.
Do not find these combinations:
GN
gn
GN
gn
Gn
gN
Is it possible to find these combinations if the genes are linked?
GN
gn
GN
gn
Gn
gN
If the genes are linked, crossing over can occur.
This helps create genetic diversity.
GN
gn
Gn
gN
Alfred Struvenat developed gene maps
• The further apart two genes are on a chromosome, the more likely they are to cross over.
• A gene map shows the frequency at which genes cross over and therefore their relative position on the chromosome.