Complex Traits of Heredity - PowerPoint Presentation

Slide1

Complex Traits of

Heredity

Chpt

. 12

Slide2

Recall Simple Types of Heredity

Recessive

 Recall, must have both recessive alleles (aa) to have a recessive trait

Autosomal

(Complete) Dominance

 Recall, only 1 allele needed to have a dominant trait (AA or

Aa

)

Slide3

Complex Patterns of Inheritance

Slide4

Complex Traits

Simple

Mendelian genetics does not explain most traitsFor example: There are at least 8 different genes associated with eye color so it isn’t so cut and dry like Mendel’s pea plants!!

Slide5

Codominance

Both Alleles Expressed Together

Slide6

Below; Both Pigmented (Red) and Non-Pigmented (White)

Both the pink and the white alleles are expressed in the heterozygote

**

RR=Red

**W

W

= White

**

R

W (Heterozygous)

~~~displays BOTH

Red

AND white alleles!!

Slide7

Codominance

in Animals

** Example: When a red horse is crossed with a white horse, a roan horse is produced. The phenotypes are:

Red (RR)

White (WW)

Occurs in cows too!!!

Roan (RW)

Heterozygous Red and White

(Hybrid)

Slide8

Codominant

Punnett Square

Roan Cow (RW)

Roan Bull (RW)

R

W

R

W

RR

R

W

R

W

WW

1Red:2Roan:1 White

25% Red

25% white

50% Roan (red AND White)

Slide9

Who’s the Father of the Calves….

Codominance

Mystery!!!

Slide10

Incomplete Dominance

– two phenotypes create a heterozygote that is intermediate between each of them; A blending of the two phenotypes to create a third phenotype

RRR’R’

Heterozygous/Hybrid

Intermediate

R’R

R’R

WHITE

RED

PINK

USE PRIMES ABOVE THE ALLELE (LETTER) FOR LACK OF PIGMENTATION…

Slide11

Incomplete Dominance

Straight Hair

H’H’

Wavy Hair

Intermediate Phenotype

H’H

(Heterozygous

)

Curly Hair

HH

Slide12

Incomplete Dominance – Hair

H

H’

H’

H

H’H

HH

H’H’

H’H

A couple, both with wavy hair, want to have a baby. What are the genotypic and phenotypic ratios of their possible offspring??

Genotypic Ratio:

1HH:2H’H:1H’H’

Phenotypic Ratio:

1Curly:2Wavy:1Straight

Slide13

X-Linked (sex linked) Traits/Disorders/Conditions

Slide14

X-linked Traits

If a Recessive

Trai

t:

X

N

X

N

= Normal

female

X

N

X

n

=

Normal Carrier

X

n

X

n

Affected female

X

N

Y= Normal Male

X

n

Y

=Affected Male

Males can NEVER

be carriers!!!!

Slide15

Colorblindness Is Recessive and On the X Chromosome

Slide16

Slide17

Hemophilia:

sex-linked recessive trait. If affected, lack a blood clotting factor.May die from a cut if left untreatedTreatment entails giving the person the clotting factor by injection

Slide18

X-linked – REMEMBER NO SUPERSCIPTS ON Y CHROMOSOME!!!

If a man is colorblind and has a child with a heterozygous female carrier………What is Dad’s genotype? Mom’s?

X

n

Y

X

N

X

n

X

n

X

N

X

N

Y

X

n

X

n

X

n

Y

1. Probability of a Colorblind Daughter??

1

of

2

Daughters or 50% of the girls

2. Colorblind Sons??

X

n

Y

X

N

X

n

1

of

2

Sons or 50% of the boys

3. Out of ALL of the children, how many are carriers??

ONLY

1

of

the four Children… Why?

Males only have 1 X!! Can’t Carry on the Y….this is X-Linked!!!

Slide19

Polygenic Traits

–

2 or more genes affect one phenotype Examples: hair color, eye color, height**Polygenic traits follow a normal distribution, bell

curve based on an average of a population

Slide20

Notice the Difference in Brightness!! Light Colors to Dark Colors!!

Slide21

A simplified model for polygenic inheritance of skin color

** Polygenic traits in a population typically follows a bell curve; lightest skin color to the left of the curve and the darkest to the

right……Notice the majority of the population is a medium tone

Slide22

Multiple Alleles

– 3 or more forms of a genes (alleles) involved in ONE trait

In the hypothetical family above, there are 6 alleles for one trait

Slide23

Blood Types are controlled by

three

alleles….…A,B and O

Slide24

Blood Types – Multiple Alleles

Phenotype Genotype

Type AB

I

A

I

B

,

or AB



Codominant

!!

Type O

ii or OO

 Recessive

Type A I

A

I

A

or AA (homozygous A)

or

I

A

i

or AO (heterozygous A)

Type B I

B

I

B

or BB (homozygous B)

or

I

B

i

, BO (heterozygous B)

Slide25

Example of a

punnett

square of a Heterozygous Type A father and Type O mother.

Slide26

Practice Punnett

Squares – Cross the Following:

A homozygous Type A female with a Type O maleA Type AB male with an O femaleA heterozygous Type B male with a heterozygous A femaleA couple that are both type AB

Slide27

Environmental Influences and Genetics

Slide28

External Factors and Internal Factors

Temperature, nutrition, light, chemicals,

hormones, age, can influence gene expression.

Slide29

External Factors

In arctic foxes temperature has an effect on the

genetic expression

of coat

color seasonally.

Slide30

External Factors

Leaves

can have different sizes, thicknesses, and shapes depending on the amount of light they receive.

Slide31

Internal Factors

Males

and females differ in hormones and structural

differences

can cause a single genotype to express more than one phenotype (antlers in males)

Slide32

Internal Factors

An organism’s age can also affect gene function

.Random mutations can accumulate

Organ function diminishes