human genetics
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Human GeneticsChapter 12
Human Genetic Traits
• Do you think this trait is dominant or recessive?
Widow’s Peak?
DOMINANT
PTC Tasting
• Can you taste the PTC????
•DOMINANT
Earlobe Shape?• Is your earlobe attached?
• Do you think this trait is dominant or recessive? RECESSIVE
Dimples?
DOMINANT
Human Inheritance
• Humans - 23 pairs of chromosomes– These are made of about 100,000 genes
• Scientists study disease causing genes because they can easily be traced– Pedigree – a family record that shows how a
trait is inherited over several generations.
PedigreeA Pedigree of Hemophilia in the Royal Families of Europe
Pedigreepage 299
• Carriers – usually, Heterozygous
-do not express the recessive allele, but pass it to their offspring
Square = Male
Circle = Female
No shading = normal
Shaded = displays trait
Half/Half = Carrier
Pedigree Practice
• Construct a family pedigree of two unaffected parents with a child who suffers from cystic fibrosis.
Pedigree Practice
• Suppose both parents can roll their tongues but their son cannot. Draw a pedigree showing this trait, and label each symbol with the appropriate genotype.
Pedigree Practice
• Describe the pedigree of a boy who has galactosemia. His father has galactosemia, his paternal grandparents are phenotypically normal. His mother and maternal grandparents are both phenotypically normal.
• A boy is an albino. His mother is also an albino. His father is phenotypically normal. However, his paternal grandfather is an albino. The other 3 of his grandparents are phenotypically normal.
• A brother and a sister both are hemophilic. Neither parent shows this trait, however the maternal grandmother suffers from this disorder. The other grandparents are phenotypically normal.
On Your Own
• Page 300
• Mini Lab 11.1 – Investigate Human Pedigrees
Simple Dominant Heredity
• Many traits are inherited just as the rule of dominance predicts.
• Remember, in Mendelian inheritance, a single dominant allele inherited from 1 parent is all that is needed for a person to show the dominant trait.
Patterns of Inheritance• Traits controlled by a Single Allele
– >200 traits are determined by a single dominant allele• Ex. Huntington’s Disease
– >250 other traits are determined by homozygous recessive alleles
• Ex. Cystic Fibrosis, PKU, blue
people in Eastern Kentucky
Sometimes Heredity Follows Different Rules
1. Incomplete Dominance: Appearance of a third phenotype
2. Sex-linked inheritance
3. Codominance: Expression of
both alleles
1. Incomplete Dominance• Incomplete dominance - Cross
between organisms with 2 different phenotypes
-produces offspring with a 3rd phenotype that is a blending of the parental traits. – RED Flower x WHITE Flower ---
> PINK Flower
• R = allele for red flowers W = allele for white flowers red x white ---> pink RR x WW ---> 100% RW
2. Sex determination• In humans, the diploid number of
chromosomes = 46 (23 pairs)– There are 22 matching pairs of homologous
chromosomes called autosomes.– The 23rd pair differs in males and females, they
determine the sex of an individual (sex chromosomes) • X females (XX)• Y males (XY)
*Complete a punnett square to determine the expected ratio of males to females produced given their possible gamete contribution
Sex-linked inheritance• Traits controlled by genes located on sex
chromosomes are called sex-linked traits
• Sex-Linked Traits are found only on the X chromosome– Ex. Hemophilia (recessive)– Ex. Patterned Baldness
• Homozygous baldness-both will lose hair
• Heterozygous-men will lose hair but women will not
– Ex. Colorblindness (recessive)
Color Blindness Activty • http://colorvisiontesting.com/ishihara.htm • http://colorvisiontesting.com/online%20test.htm • Draw your family pedigree for color blindness!
• Predict what your children genotype could be if: – Boys – you married a woman who carried the trait for being color
blind on her X chromosome– Girls – you married a man who was color blind
Patterns of Inheritance
• Complete a punnett square to show how the allele for red eye color is a sex-linked trait
3. Codominance• Codominance - the "recessive" & "dominant"
traits appear together in the phenotype of hybrid organisms.
• Example:
red x white ---> red & white spotted
• R = allele for red flowers W = allele for white flowers red x white ---> red & white spotted RR x WW ---> 100% RW
Examples of Codominance1. Roan fur in cattle
– Cattle can be:1. red (RR = all red hairs)2. white (WW = all white hairs)3. roan (RW = red & white hairs together)
2. Human blood type: AB-2 types of protein ("A" & "B") appear together on the surface of blood cells
– How to determine Blood Types:– 4 possible blood types (in order from most
common to most rare): O, A, B and AB.
– O blood type = individual who is homozygous recessive (ii) and does not have an allele for A or B.
• Blood types A and B are codominant alleles. – Recessive allele i (for blood type O) is only
expressed when 2 recessive alleles are present.
– Individuals who have blood type A:• Genotype = IAIA or IAi
– Individuals who have blood type B:• Genotype = IBIB or Ibi
– Individual who has blood type AB:• Genotype = IAIB
– Individual who has blood type O:• Genotype = ii
Human Blood Types
– Blood transfusion can only take place between 2 people who have compatible types of blood.
– Human blood is separated into different classifications because of the varying proteins on the surface of blood cells.
– These proteins are there to identify whether or not the blood in the individual's body is it's own and not something the immunity system should destroy.
**IMPORTANCE in Real-Life**
Blood type practiceUse a Punnett Square!
1. A woman has type A blood. Her father has type O blood. The woman marries a man with type O blood. What is the chance that they will have a child with type A blood?
2. What is the chance that the couple from question 1 will have a child with type AB blood?
*Show me your answers when you are finished. Keep these in your notes!
Sickle Cell Anemia• Read about
Codominance on pg. 302-303
• Define Codominance.
• Explain Sickle-cell Disease in ½ page.
• Complete Data Analysis Lab 11.1 on the bottom ½ of the page.
Sickle Cell Anemia Cont.
• A Mutation Story:
http://www.teachersdomain.org/resource/tdc02.sci.life.gen.lp_disorder/
Nondisjunction
• Nondisjunction is the failure of homologous chromosome pairs to separate properly during meiosis. The result of this error is a cell with an abnormal (too few or too many) number of chromosomes.
Nondisjunction
Activity: Human Karyotype
Patterns of Inheritance
Child with Trisomy 21
Disorders due to Nondisjunction Cont. – Klinefelter’s (XXY)-male w/ some female
traits
– Turner’s (XO)-female appearance• Single Y chromosome do not survive
• Typically Sterile
Environmental Effects
• Genes are inherited from parents, but sometimes their expression is modified by environmental factors.
• An example is the snowshoe hare we discussed earlier in the year-these hares have dark fur in the summer and white fur in the winter.
Snowshoe Hare
Detecting Human Genetic Disorders
• Genetic Screening – examination of genetic makeup– Karyotype: a picture of chromosomes
grouped in pairs and arranged in sequence.
– Screening of Blood: look for certain proteins• Genetic Counseling-medical guidance
informing of problems that could affect their offspring.
Detecting HumanGenetic Disorders
– Amniocentesis: removal of small amount of amnionic fluid surrounding the fetus
– Chorionic Villi Sampling: tissue that grows between the mother’s uterus and the placenta (between the 8th and 10th week)
– Screening Immediately after Birth:• Ex PKU (Phenylketonuria)-body cannot
metabolize the amino acid phenylalanine– Special diet lacking phenylalanine
Karyotyping
• http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping2.html
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