Chapter 11

INTRODUCTION TO

GENETICS

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

- Cross-pollinate: Male and female gametes are from two

different plants

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

Page 310

III. Mendel’s Experiment

A. Crossed plants with contrasting traits

1. Studied seven traits

2. First crossed monohybrid (one trait) plants P = parents

F1 = first filial generation

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

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

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)

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

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

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)

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

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

C. Multiple Alleles (Page 320)1. More than 2 alleles are available

Example: eye color, rabbit fur color

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)

E. Genes & the Environment (page 321)

1. Environmental conditions can affect gene expression & influences

genetically determined traits.

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

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

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

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

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.

Meiosis I Page 324

Interphase I

Prophase I

Meiosis I

Metaphase I Anaphase ITelophase I

and Cytokinesis

3. Meiosis II

a. Prophase II

- Spindle fibers formsProphase II

b. Metaphase II

- Chromosomes line up in the middle of

the cell

Metaphase II

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)

Meiosis IIPage 325

Telophase I and Cytokinesis I

Meiosis II

Prophase II Metaphase II Anaphase IITelophase II

and Cytokinesis

X. Gamete Formation

A. In male animals, meiosis results in four equal-sized gametes called sperm.

B. In many female animals, only one egg results

from meiosis. The other three cells, called polar

bodies, are usually not involved in reproduction.

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

2N = 4 N = 2

Comparing Mitosis and Meiosis

prophase (I)

metaphase (I)

anaphase (I)

telophase (I)

End of Meiosis I

End of Meiosis II

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

Page 328