Genetics What makes each species unique? - PowerPoint Presentation

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Genetics What makes each species unique? - PPT Presentation

Heredity The passing of genetic traits from parent to offspring The scientific study of heredity is known as genetics The History Until the nineteenth century the explanation for why offspring resemble their parents was the blending inheritance model ID: 930953

alleles rryy genes cross rryy alleles cross genes offspring ratio tall dominant red traits phenotype chromosomes white ggnn short

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Slide1

Genetics

Slide2

What makes each species unique?

Heredity:The passing of genetic traits from parent to offspring.The scientific study of heredity is known as:

genetics

Slide3

The History:

Until the nineteenth century the explanation for why offspring resemble their parents was the blending inheritance model.Blending inheritance: The hypothesis that factors from both parents

mix in the offspring.

Like mixing yellow and blue to make green

Slide4

Gregor Mendel

(1822-1884):The founder of modern genetics. Worked with garden peas because:

They have easily distinguished traits

self-fertilize in nature

Slide5

Worked with garden peas because:

All were true-breeding:

self-fertilization produces offspring

identical to the parent.

Slide6

Mendel cross-pollinated the plants

by mating his different true breeding varieties

with each othe

Mendel’s Experiments:

Studied traits: 7 characteristics that all had

two distinct forms

Trait:

a specific characteristic that varies from one individual to another

Slide7

Slide8

Original pair of plants were called P (

Parental

)

Offspring were called F1 (

first Filial

)

Hybrids:

the

offspring

that result from crossesbetween parents

with different traits

Slide9

When crossing two different parents, what were the offspring like?

P: tall plant X short plant

F1:

All tall offspring

Slide10

Mendel’s Conclusions:

1. Inherited traits are determined by factors that are passed from one generation to the next.Today these factors are called

genes.

Slide11

Mendel’s Conclusions:

Alleles: The different forms of a gene – each is given a letter. Ex: The gene for height has a

tall plant

allele (T) and a short plant allele (t).

Slide12

Mendel’s Conclusions:

2. The principle of dominance: Some alleles are dominant and others are recessive

If an organism has a

dominant form

of an allele for a trait, the organism will always show that form.

Dominant alleles are written with a capital letter.

Slide13

If an organism has a

recessive form of a trait, it will only show if the dominant allele is NOT present.

Recessive alleles are written with a lower-case

letter.

Slide14

Let’s look back at Mendel’s experiment. The cross of tall and short plants resulted in all tall hybrid offspring.

The recessive allele reappeared in the F2 generation!

parental

Slide15

Mendel’s Conclusions:

3. Principle of Segregation: During gamete formation, alleles are

segregated

from each other so that each gamete carries only a

single copy of each gene.

The alleles are paired up again when the gametes fuse during fertilization.

Slide16

Gametes

Principle of Segregation

Slide17

Probability and Punnett Squares:Mendel realized that the principle of probability could be used to explain the results of his genetic crosses.

Probability: The likelihood that a particular event will occur What is the probability of flipping heads twice?

The

principles of probability can be used

to predict the

outcomes of genetic crosses

We can determine the probable results

of a genetic cross by drawing a Punnett square

½ X ½ = ¼

Slide18

Let’s cross the F1 generation plants from Mendel’s garden

Parents: Tt x Tt

Two types of gametes produced by each parent

Slide19

Homozygous:

having two of the same allele.

Ex: TT or

Heterozygous:

having two different alleles.

Ex: Tt

Phenotype: the

physical characteristics of the organism

Ex: “Tall plant”

or “short plant”Genotype:

The

gene

tic makeup of an individual

(

the actual

alleles)

Ex:

Slide20

Note:

If a plant has a tall phenotype, it can have one of two genotypes

Phenotype:

tall plant;

Genotype:

TT OR

Slide21

Trait

phenotype

genotype

Height

“T”

Tall-dom.

Short-rec

Hair color

“B”

Black-dom

red-rec.

Fill in the table below with the appropriate phenotype or genotype for the given trait

tall

TT or Tt

short

BB or Bb

black

red

Slide22

Problem:

Cross a heterozygous tall plant with a heterozygous tall plant. Use the letter “T.”

___ X

___

Gametes:

Genotypes of offspring:

Phenotypes of offspring:

Genotypic ratio: (example 1 TT : 1

)

Phenotypic ratio: (example 1 tall : 1 short)

TT,

Tall & short

1TT: 2Tt: 1tt

3 tall: 1 short

Slide23

Note: The larger the number of individuals in the sample,

the closer the results will be to the expected ratio.

Slide24

Try a monohybrid (single-trait cross) problem:

In rabbits, brown fur (B) is dominant to white fur (b).

Cross

a homozygous brown furred rabbit with a white furred rabbit

and

determine the genotypic and phenotypic ratios resulting from the cross

. Use a

Punnett

Square to show your work.

P: __________________X_______________

Phenotypic ratio:

Genotypic ratio:

all brown

all Bb

Slide25

If one of the parent rabbits has white fur

and the other has brown fur, is there anyway they could get an offspring with white fur? Do a cross to support your answer. P: __________________X_______________

Phenotypic ratio:

Genotypic ratio:

brown: 1 white

1Bb

: 1bb

Slide26

Test cross: a cross with a recessive individual and a dominant individual to see if a

dominant individual is heterozygous or homozygous.

Slide27

When two traits are inherited, are the two characteristics inherited as a package or are they inherited independently of each other?

The Two-Factor Cross:Mendel crossed true-breeding plants with

round yellow peas

with plants that had

wrinkled green peas.

(Use “R” for shape and “Y” for color)

P cross: RRYY x rryy

F1 cross:RrYy x RrYy

F2 generation: Produced 556 seeds315 round and yellow

32 were wrinkled and green209 had combinations of traits different from both original parents.

Slide28

4. Principle of Independent Assortment:

Each pair of alleles segregates independently of the other pairs of alleles during gamete formation.

Let’s show how this occurs

: Gametes:

Ry rY

RRYY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

rrYY

RrYy

RrYY

RrYy

Rryy

rrYy

rryy

Slide29

9 Round Yellow:

3 Round Green:

3 Wrinkled Yellow:

1 Wrinkled Green

The expected phenotypic ratio in the F2 generation:

Mendel’s results were very close to this expected ratio.

Slide30

Let’s try another Dihybrid Cross:

Brown eyes (B) and tongue rolling (R) are dominant traits in humans. These traits are dominant over blue eyes and non-tongue rolling. A

heterozygous brown eyed, non-tongue roller

female marries a

blue eyed, heterozygous tongue roller

male and they have children.

What is the genotype of the wife?

What is the genotype of the husband?

Slide31

Exceptions to Mendel:So far all of our problems have dealt with complete dominance. However, some alleles are neither dominant nor recessive, and many are controlled by multiple alleles or multiple genes.

1. Incomplete dominance: one allele is not completely dominant over another

The heterozygous phenotype is in between

the two

homozygous phenotypes

Example: In the Japanese 4 o’clock flower , a red flower (R) crossed with a white flower (W) will produce offspring with pink flowers (a blending of the phenotypes)

Genotypic ratio:

Phenotypic ratio:

All pink

All RW

Slide32

Exceptions to Mendel:

2. Co-dominance:

both alleles contribute to the phenotype

Example: In cattle, red hair and white hair are codominant.

Cattle with both alleles are roan

(both alleles appear in the phenotype: red hairs & white hairs)

Cross a Roan cow with a Red Bull:

Genotypic ratio:

Phenotypic ratio:

: 1H

1Red: 1Roan

Slide33

3. Multiple alleles: Some genes have more than just 2 alleles

Example: human blood has three alleles: A, B, and O.

Exceptions to Mendel:

A blood:

OR I

AiB blood: I

BIB OR IB

i AB blood: IA

IB O blood:

Human Blood Types

(Phenotype:Genotype)

Slide34

As long as we are talking about blood types….

Rh Blood Group (not

a case of multiple alleles)

Phenotype: Genotype

+ or Rh

+ Rh

-Rh-:

Rh- Rh

Slide35

4. Polygenic traits:

One trait is controlled by 2 or more genesExample: Human height, skin color

Exceptions to Mendel:

Slide36

Exceptions to Mendel:

5. Pleiotropy:

One gene influences multiple characteristics

Example:

Sickle-cell anemia

Slide37

Sex-linkage: genes located on one of the

sex chromosomes are called sex-linked.

There are two types of chromosomes in animals:

Autosomes

The chromosomes that are

not

involved

in determining gender.

Sex chromosomes: The “mismatched” chromosomes that determine the gender of the organism (Female = XX ; Male = XY)

Example: hemophilia &red green colorblindness

Slide38

Write the following genotypes:

Colorblind male:

___________

Female carrying the colorblind gene:

___________

Male with normal vision:

___________

XCX

XCY

Colorblindness is a recessive sex-linked trait

Genotypes of sex-linked traits are written with a superscript

Slide39

Example: The gene for eye color in fruit flies is located on the X chromosome. Red eye color is dominant to white eye color. A

white eyed male is crossed with a homozygous red eyed female. Determine the genotypes and phenotypes of the F1 generation.

Genotypic Ratio:

Phenotypic Ratio:

1 red eyed female:

1 red eyed male

Slide40

The Chromosome Theory of Heredity

Where in the cell are the factors that control heredity? Where are the genes?

Chromosomal theory of heredity:

Genes occupy specific

positions on chromosomes.

Chromosomes undergo

independent assortment & segregation

Slide41

Linked Genes:

Linkage groups:

Genes are linked together in chromosomes

Genes that are close together are likely to be inherited together

a chromosome

Slide42

Thomas Hunt Morgan: (1900’s)

Worked with fruit flies, In fruit flies Gray bodies (G) is dominant over black (g) and Normal wings (N) are dominant over vestigial wings (n). He first crossed a homozygous gray, normal winged fly (GGNN) with a black, vestigial winged fly (

ggnn

). He expected the F1 flies to be:

He then performed a test cross with

the F1 generation.

Drosophila

melangaster

gray with normal wings

All F1 flies were gray w/ normal wings

GgNn

ggnn

Slide43

GgNn X