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Complex Traits of Heredity Chpt . 12. 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 ) . - PowerPoint PPT Presentation
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Complex Traits of HeredityChpt. 12
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)
Complex Patterns of Inheritance
Complex TraitsSimple 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!!
CodominanceBoth Alleles Expressed
Together
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!!
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)
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)
Who’s the Father of the Calves….Codominance Mystery!!!
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…
Incomplete Dominance
Straight HairH’H’
Wavy Hair Intermediate
PhenotypeH’H
(Heterozygous)Curly Hair
HH
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
X-Linked (sex linked) Traits/Disorders/Conditions
X-linked TraitsIf a Recessive Trait: XNXN = Normal female XNXn = Normal CarrierXnXn Affected femaleXNY= Normal MaleXnY=Affected Male
Males can NEVER be carriers!!!!
Colorblindness Is Recessive and On the X Chromosome
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
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 YXN 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!!!
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
Notice the Difference in Brightness!! Light Colors to Dark Colors!!
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
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
Blood Types are controlled by three alleles….…A,B and O
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)
Example of a punnett square of a Heterozygous Type A father and Type O mother.
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
Environmental Influences and
Genetics
External Factors and Internal
Factors• Temperature, nutrition, light, chemicals, hormones, age, can influence gene expression.
External Factors• In arctic foxes
temperature has an effect on the genetic expression of coat color seasonally.
External Factors• Leaves can have different sizes, thicknesses,
and shapes depending on the amount of light they receive.
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)
Internal Factors• An organism’s age can also affect gene
function.• Random mutations can accumulate• Organ function diminishes