Download - Complex Traits of Heredity Chpt . 12
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Complex Traits of Heredity
Chpt. 12
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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)
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Complex Patterns of Inheritance
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Complex Traits
Simple Mendelian genetics does not explain most traits
For 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!!
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CodominanceBoth Alleles Expressed
Together
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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 **RW (Heterozygous) ~~~displays BOTH Red AND white alleles!!
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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)
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Codominant Punnett Square
Roan Cow (RW)
Roan Bull (RW)
R
W
R W
RR R W
R W WW
1Red:2Roan:1 White25% Red25% white50% Roan (red AND White)
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Who’s the Father of the Calves….Codominance Mystery!!!
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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 REDPINK
USE PRIMES ABOVE THE ALLELE (LETTER) FOR LACK OF PIGMENTATION…
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Incomplete Dominance
Straight HairH’H’
Wavy Hair Intermediate
PhenotypeH’H
(Heterozygous)
Curly HairHH
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Incomplete Dominance – Hair
H
H’
H’
H H’HHH
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
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X-Linked (sex linked) Traits/Disorders/Conditions
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X-linked TraitsIf a Recessive Trait: XNXN = Normal female XNXn = Normal CarrierXnXn Affected femaleXNY= Normal MaleXnY=Affected Male
Males can NEVER be carriers!!!!
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Colorblindness Is Recessive and On the X Chromosome
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Hemophilia: sex-linked recessive trait. If affected, lack a blood clotting factor.
May die from a cut if left untreated
Treatment entails giving the person the clotting factor by injection
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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?
Xn Y
XN Xn
Xn
XN XN Y
Xn Xn Xn
Y
1. Probability of a Colorblind Daughter??
1 of 2 Daughters or 50% of the girls
2. Colorblind Sons??
Xn
YXN
Xn
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!!!
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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
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Notice the Difference in Brightness!! Light Colors to Dark Colors!!
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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
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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
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Blood Types are controlled by three alleles….…A,B and O
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Blood Types – Multiple Alleles
Phenotype Genotype
Type AB IAIB , or AB Codominant!!
Type O ii or OO Recessive
Type A IAIA or AA (homozygous A)or
IAi or AO (heterozygous A)
Type B IBIB or BB (homozygous B)or
IBi, BO (heterozygous B)
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Example of a punnett square of a Heterozygous Type A father and Type O mother.
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Practice Punnett Squares – Cross the Following:
A homozygous Type A female with a Type O male
A Type AB male with an O female
A heterozygous Type B male with a heterozygous A female
A couple that are both type AB
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Environmental Influences and
Genetics
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External Factors and Internal
Factors• Temperature, nutrition, light, chemicals, hormones, age, can influence gene expression.
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External Factors• In arctic foxes
temperature has an effect on the genetic expression of coat color seasonally.
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External Factors• Leaves can have different sizes, thicknesses,
and shapes depending on the amount of light they receive.
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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)
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Internal Factors• An organism’s age can also affect gene
function.• Random mutations can accumulate• Organ function diminishes