INTRODUCTION TO GENETICS › uploads › 1 › 0 › 9 › 7 › 109790705 › 20… ·...
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Chapter 11
INTRODUCTION TO
GENETICS
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11-1 The Work of Gregor Mendel
I. Gregor Mendel
A. Studied pea plants
1. Reproduce sexually (have two sex cells = gametes)
2. Uniting of male and female gametes = Fertilization
3. Pollination = Transfer of pollen from male part of plant to
female part of planta. Two Types:
- Self-pollinate:Male and female gametes come from same
plant, offspring are identical to parents
*Allows for true breeding:
Produce identical offspring to self
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- Cross-pollinate: Male and female gametes are from two
different plants
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II. Laws of Heredity
A. Heredity: Passing on of characteristics from parents to
offspring
B. Genetics:Study of heredity
C. Traits: Specific characteristic
E. Genes: Determines traits
F. Alleles: Forms of a gene
D. Hybrid: Offspring of crosses btw parents with different
traits
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Page 310
III. Mendel’s Experiment
A. Crossed plants with contrasting traits
1. Studied seven traits
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2. First crossed monohybrid (one trait) plants P = parents
F1 = first filial generation
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F2 = second filial generation
Example: P = tall x short
F1= all tall
Self-pollinate: F1 x F1
F2= ¾ tall, ¼ short 3:1 ratio
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B. Mendel’s Conclusions: Biological inheritance is determined by
factors (genes) passed from one generation to the next that
follow 3 Laws.
1. Law of Dominance:
Some alleles are dominant and
others are recessive
2. Law of Segregation:
gametes randomly pair producing
four combinations of alleles
3. Law of Independent Assortment:
Pairs of genes separate
independently from each other
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11-2 Applying Mendel’s Principles
IV. Probability
A. Likelihood a particular event will occur
B. Can be used to predict the outcomes of genetic
crosses
V. Punnett Squares
A. Visual diagram to find all possible genetic
variations of offspring of a cross
B. Phenotype
1. Physical characteristic (looks/behavior/you
can see it)
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C. Genotype
1. Genetic make-up
2. Made up of alleles
3. Three combinations
a. Homozygous Dominant TTb. Homozygous recessive ttc. Heterozygous Tt
D. Example:
Cross: Homozygous Dominant X Homozygous Recessive
Cross: Heterozygous X Heterozygous
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VI. Dihybrid Cross (2 traits)
A. Round Yellow RRYY x wrinkled green rryy
B. F1= RrYy
C. F1 x F1 (self-pollinate)
Page 317
*To find the allele combinations for
the gametes you have to FOIL
FOIL = First Outside Inside Last
RY Ry rY ry
R r Y y
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D. 9 Round Yellow, 3 Round Green
3 wrinkled Yellow, 1 wrinkled green
E. Get a 9:3:3:1 Ratio of Phenotypes
F. Law of Independent Assortment:
Genes for different traits are inherited
independently from each other during
gamete formation
VI. Dihybrid Cross (2 traits)
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Summary of Mendel’s Principles
Inheritance is determined by units called , which are
passed from parents to offspring.
Where more than one form of a gene for a single trait exists,
some alleles may be and others .
Each adult has two copies of each gene—one from each
parent. These genes from each other when
gametes are formed.
Alleles for different genes usually segregate of
each other.
genes
dominant recessive
segregate
independently
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VII. Modes of Inheritance
A. Incomplete Dominance (Page 319 Figure 11-12)
1. Neither allele is dominant or recessive, so they
mix together
2. Phenotype somewhere between the two alleles
Example: Red (RR) x White (WW) = PINK (RW)
B. Codominance
1. Both alleles are dominant & contribute to phenotype
Example: Black Rooster (BB) x White Hen (WW)
= Checkered Chickens (BW)
11-3
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C. Multiple Alleles (Page 320)1. More than 2 alleles are available
Example: eye color, rabbit fur color
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D. Polygenic Traits
1. Traits controlled by more than 2 genes
Example: human skin color (at least 4 genes), most
human traits
(= Many Genes for a trait)
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E. Genes & the Environment (page 321)
1. Environmental conditions can affect gene expression & influences
genetically determined traits.
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11-4 Meiosis
VIII. Chromosome Number
B. Haploid
1. Chromosome appear in pairs
(2 sets of chromosomes 1 from
mom and 1 from dad)
2. n
C. Diploid
1. Gamete cell has one of each kind of chromosome
2. 2n
A. Homologous Chromosomes
1. Paired chromosomes with genes of same
traits in same order
2. Not always identical
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IX. Meiosis
A. Occurs in specialized cells that produce gametes
1. Gamete = sperm/ovum
B. Organisms inherit a single copy of every gene from each parent
C. Produces gametes with only 1 set of genes
D. Two divisions
1. Meiosis I and Meiosis II
2. Diploid (2n) cell at beginning of Meiosis I and 4 haploid
(n) cells at the end of Meiosis II
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1. Interphase
a. DNA replicates
2. Meiosis I
a. Prophase I
- Chromosomes pairs with its corresponding homologous
chromosome (matched gene by gene = TETRAD)
- Non-sister chromatids overlap & exchange material =
Crossing Over (Page 324)
Interphase I
Prophase I
E. Stages
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b. Metaphase I
- Paired homologous chromosomes line up across center of the cell
Metaphase I
c. Anaphase I
- Homologous chromosomes separate by fibers and move to
opposite ends of the cell
Anaphase I
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d. Telophase I and Cytokinesis
- Nuclear membranes form and cell separates
Telophase I
*The two cells produced by meiosis I have chromosomes
and alleles that are different from each other and from the
diploid cell that entered meiosis I.
e. The two cells enter a second meiotic division.
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Meiosis I Page 324
Interphase I
Prophase I
Meiosis I
Metaphase I Anaphase ITelophase I
and Cytokinesis
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3. Meiosis II
a. Prophase II
- Spindle fibers formsProphase II
b. Metaphase II
- Chromosomes line up in the middle of
the cell
Metaphase II
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c. Anaphase II
- Centromere splits sister chromatids
and go to opposite ends of the cell
Anaphase II
d. Telophase II and Cytokinesis
- Nuclei reform, spindle fibers
break down, cytoplasm divides
Telophase II
e. END RESULT: 4 haploid cells (different)
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Meiosis IIPage 325
Telophase I and Cytokinesis I
Meiosis II
Prophase II Metaphase II Anaphase IITelophase II
and Cytokinesis
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X. Gamete Formation
A. In male animals, meiosis results in four equal-sized gametes called sperm.
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B. In many female animals, only one egg results
from meiosis. The other three cells, called polar
bodies, are usually not involved in reproduction.
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XI. Comparing Mitosis and Meiosis
Mitosis vs Meiosis
1 division 2 divisions
2 identical diploid cells 4 different haploid cells
Body cells (skin, muscle,..etc.) Sex cells (gametes)
½ the # of chromosomes as
parent cell
Same # of chromosomes as
parent cell
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2N = 4 N = 2
Comparing Mitosis and Meiosis
prophase (I)
metaphase (I)
anaphase (I)
telophase (I)
End of Meiosis I
End of Meiosis II
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11-5 Linkage and Gene maps
XII. Gene Linkage
A. Chromosomes are groups of linked genes
B. Chromosomes assort independently not the genes
XII. Gene Maps
C. Crossing over sometimes separates genes on
chromosomes = Genetic Diversity
A. Shows distance between genes on chromosomes
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