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.