Complex Inheritance and Human HeredityChapter 11

Let’s review!

• We inherit traits from our parents, we get half of our genes from mom, and half from dad

• Alleles are either recessive (lowercase) or dominant (uppercase)

• Homozygous recessive, homozygous dominant, heterozygous

New Words!

• Autosome/Autosomal: Any chromosome other than the sex chromosomes (X & Y). Chromosomes designated 1-22.

• Carrier: An individual who is heterozygous for a recessive disorder

• Pedigree: A diagram that traces the inheritance of a particular trait through several generations of the same family

BASIC PATTERNS OF INHERITANCEGenetic Disorders

Genetic Disorders

• An abnormal condition that a person inherits through their genes

• Can be caused by either changes in DNA, or an extra or missing chromosome

• Genetic disorders can be recessive or dominant

Recessive Disorders

• Two recessive alleles, one from each parent

• If an individual is heterozygous, they are a carrier (this means they could pass it on even if they don’t have it!)• BB – Normal• Bb – okay, but a carrier• bb – disease

• Often skips a generation

Cystic Fibrosis

• Affects cell membrane protein, water cannot diffuse from cells

• the body produces an abnormally thick mucus in the lungs

• Chromosome 7• Medication, strict diet,

enzyme replacement• Death is usually caused by lung

complications

Tay-Sachs

• Absence of enzyme that breaks down fatty substances

• Chromosome 15• Buildup of fatty acids in brain• Cherry red spot on back of eye• Causes deafness, blindness,

severe retardation, and death usually by age 4

• Most carriers choose to avoid birth because there is no cure

Albinism

• Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes• White hair• Very pale skin• Pink pupils

Galactosemia

• Recessive genetic disorder characterized by the inability of the body to digest galactose.

• People with this disorder should avoid milk products

OGT

The mutation for cataracts (c) occurs on a gene represented by the letter E. Owls that are homozygous for the mutation (EcEc) exhibit cataracts. Owls that are homozygous for normal eyes are EE and owls that are carriers of the mutation but do not exhibit cataracts are EEc.  What percentage of the offspring in a cross between parents with the genotypes EE and EcEc will exhibit cataracts?  A. 0% B. 25% C. 50% D. 75%

Dominant Disorders

• Caused by dominant alleles

• Those who do not have the disorder are homozygous recessive.• BB – have disease• Bb – have disease• bb – normal

Huntington’s Disease

• Affects the nervous system• Deterioration of brain

tissue, usually begins between age 30 and 40

• Chromosome 4• No cure, but have

medications to cope with symptoms

• People usually die 15-20 years after onset of degeneration

Achondroplasia

• causes small body size and limbs that are comparatively short, most common type of dwarfism

• Chromosome 4• 75% born to parents of

average size• When this happens it is

due to a gene mutation

GENETIC DISORDERSTo Test or Not to Test?

Choosing Thomas

• You will need one worksheet and one index card• Find the rest of your family based on the number on your

cards• Complete the worksheet as a group and be prepared to

discuss your answers as a class

PEDIGREES

Pedigrees

• A diagram that traces the inheritance of a particular trait through several generations of the same family

• Allows us to use family trees and affected individuals to predict the risk of disease in future offspring

Symbols

• Male: • Female:

• Affected Individual:

• Carrier:

• Mating:

• Siblings:

• Divorced/Separated:

• Deceased:

• Individuals are in birth order from left to right (oldest at left, youngest on right)

• Individuals are numbered• Generations are numbered with roman numerals• When referring to an individual, use the generation

number and then the individual number• II-4

Example of a Pedigree

You

Parents

Aunts, UnclesAunts, Uncles

GrandparentsGrandparents

BrotherDo any disorders run in this family??

I

III

II

What can you tell from a pedigree?

• Whether a family has an autosomal or sex-linked disease or disorder• If the trait is dominant or recessive• Autosomal: appears in both sexes equally• Sex-linked disorder: allele is located only on the X or Y chromosome.

Most sex-linked genes are on the X chromosome and are recessive• So who would have an X-linked disorder more often, boys or girls?

COMPLEX PATTERNS OF INHERITANCE

Let’s Review!

• Basic patterns of inheritance involve…• The passing of dominant or recessive traits

• Disorders that are recessive require:• 2 recessive alleles, 1 from mom, 1 from dad• A normal person who carries the gene could pass it on

• Disorders that are dominant require:• 2 dominant alleles, 1 from mom, 1 from dad OR• 1 dominant allele (heterozygous)• There are no carriers for these disorders, you either have it

or you don’t!

Let’s Review!

• These disorders are autosomal• Chromosomes 1-22

• Geneticists use a diagram called a pedigree to trace familial traits and predict the inheritance of the trait in future offspring

• Sometimes the laws and principles of genetics established by Gregor Mendel do not always explain the inheritance patterns seen in an organism.

Incomplete Dominance

• Neither allele is completely dominant nor completely recessive

• Heterozygous phenotype is a blend of the two homozygous phenotypes• a mix in physical

appearance between the dominant and the recessive

Codominance

• Both alleles are completely expressed in the heterozygous condition. • Sickle Cell

Sickle Cell Anemia

• Abnormal hemoglobin causes a person’s red blood cells to be sickle shaped• The shape causes clots and blockages, they also carry less

oxygen• The allele for the disease is codominant with the normal

allele (heterozygous)• People who are heterozygous for sickle cell also have a

higher resistance to malaria

Sickle Cell

• rr – all sickle shaped cells

• Rr– mixture of both• RR– normal shaped

cells

Codominant or Incomplete?

Multiple Alleles

• Sometimes, there are 3 or 4 alleles that code for a single trait• Blood Groups

• This doesn’t mean a person has more than 2 alleles for the trait, just that more than 2 exist in the population

•1 gene, more than 2 alleles

Blood Groups

• 3 forms of the allele• IA – type A• IB – type B• i – type O

• i is recessive to IA and IB

• IA and IB are codominant• IAIB – type AB

Blood Groups

Heterozygous• IAi – type A• IBi – Type B• IAIB – type AB

Homozygous• IAIA – Type A• IBIB – Type B• ii – Type O

OGT

 A scientist uses a microscope to examine two slides of living bacteria. Each slide contains a different type of bacteria. While the cells on the first slide are moving rapidly, the cells on the second slide are stationary.  Based on these observations, the cells on the second slide most likely have no  A. nucleus B. flagella C. chloroplasts D. mitochondria

Sex-Linked Traits

• Genes that are found on the X chromosome

• Expressed more in males because they only have one X chromosome (XY) compared to females (XX)

Hemophilia

• Recessive sex-linked disorder

• Takes a long time for blood to clot (body lacks proteins involved in clotting)

• Very rare in females because she would need to have both X chromosomes with the recessive trait.

Patricia is a healthy carrier of hemophilia and Sam is completely healthy. Complete the Punnett square below. • Mom’s genotype: • Dad’s genotype:• What is the probability of getting: • Daughter with hemophilia? • Son with hemophilia?• Carrier? • Healthy child?

Red-Green Colorblindness

• Recessive X-linked trait• Male only needs one copy of

this allele in order to be colorblind.

• Female would need to have two copies of the recessive allele.

• It is very rare to find a color blind female.

• Mothers pass this to their sons• Father pass it to their

daughters

Judy is homozygous recessive for colorblindness and Dennis is healthy. Complete their Punnett square below.

• Mom’s genotype:• Dad’s genotype: • What is the probability of getting: • Colorblind daughter? • Color blind son? • Carrier?• Heterozygous child?

Baldness

Baldness is X-linked RecessiveGrandpa bald = XbY X Grandma = XBXB

Daughter = XBXb marries Male = XBY Sons?

50% XB(normal) 50% Xb(bald)

This is why men should look to their mom’s dad for probability of baldness. But beware grandma could be a carrier too!

OGT

At 25°C, water has a density of 1.0 g/mL and vegetable oil has a density of 0.90 g/mL.  How would a substance with a density of 0.95 g/mL behave when placed in both oil and water?  A. a decrease in air quality. B. a decrease in biodiversity. C. an increase in deciduous tree species. D. an increase in nighttime temperatures.

What’s different?

Nondisjunction

• Cell division during which sister chromatids fail to separate properly

• If this occurs during Meiosis I or II then the resulting gametes will not have the correct number of chromosomes

• Nondisjunction occurs in both autosomes (body cells) and in gametes

• Trisomic: one extra chromosome (only 3 trisomies that result in survival after birth)

• Monosomic: one missing chromosome (usually lethal, except in Turner’s Syndrome)

http://www.youtube.com/watch?v=EA0qxhR2oOk

Down Syndrome

• Chromosome 21• Trisomy

• Can be moderate or severe• Short stature, heart

defects, and mental disability

• Correlated with mother’s age, can be from nondisjunction of father’s chromosome 21

Other Examples

Autosomal• Patau Syndrome: Trisomy 13• serious eye, brain, circulatory

defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months

• Edwards’s Syndrome: Trisomy 18• almost every organ system

affected 1:10,000 live births. Children with full Trisomy 18 generally do not live more than a few months.

Sex Chromosomes• Klinefelter Syndrome: XXY• Male sex organs; unusually small

testes, sterile. Breast enlargement and other feminine body characteristics. Normal intelligence.

• Trisomy X: XXX• 1:1000 live births - healthy and fertile

- usually cannot be distinguished from normal female

• Monosomy X: Turner’s Syndrome• 1:5000 live births; the only viable

monosomy in humans - women with Turner's have only 45 chromosomes!!! XO individuals are genetically female, however, they do not mature sexually during puberty and are sterile. Short stature and normal intelligence. (98% of these fetuses die before birth)

Environmental Factors

• The environment can have an influence on how genes are expressed• Toxic agents• Diet and exercise• Sunlight and water• Temperature• Medications

• Conditions can cause a gene to shut down or turn on I got the “fat” gene.

Additional Vocabulary

• Karyotype: an image that shows homologous chromosomes arranged in decreasing size

• Telomere: caps on the ends of chromosomes, have a protective function

Epistasis

• BBC: The Ghost in Your Genes• Epistasis: When the one gene hides the effects of another

gene• Epigenetics

OGT

A driver traveling from the coniferous region to the tundra region would most likely observe A. sink in both oil and water B. sink in oil and float on water C. float on oil and sink in water D. float on both oil and water