inheritance patterns & human genetics
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Inheritance Patterns & Human Genetics
Chapter 12
Chromosomes & Inheritance
Section 12.1
What makes human males different than females?
Sex chromosomes (X and Y) Male: XY Female: XX
Gametes: Egg: carry only X Sperm: carry either X or Y
Who Discovered Sex Chromosomes? Thomas Morgan
Early 1900s Geneticist, embryologist, evolutionary
biologist, Columbia University (USA) Worked with fruit flies; discovered the
role chromosomes play in inheritance
Sex Linkage: When genes are found on the sex
chromosomes
X-linked Genes: genes on the X chromosome
Y-linked Genes: genes on the Y chromosome
Sex Linked Traits Most sex linked
genes are found on the X chromosome
Only genes on the Y chromosome are for male reproductive organ development
Sex Linked Genetic Problems In flies: R = red eyes, r = white eyes
Gene located on the X chromosome
X X
Y
X
Example 1: White eye male mates with a red
homozygous dominant female
XrY x XRXR
XRXr XRY
XRXr XRY
Xr Y
XR
XR
100 % red female 0 % white female
100 % red male 0 % white male
Example 2: Red eye male mates with a red
heterozygous female
XRY x XRXr
XRXR XRY
XRXr XrY
XR Y
XR
Xr
100 % red female 0 % white female
50 % red male 50 % white male
Example 3: White eye male mates with a red
heterozygous female
XrY x XRXr
XRXr XRY
XrXr XrY
Xr Y
XR
Xr
50 % red female 50 % white female
50 % red male 50 % white male
Linkage Groups Genes located on the same
chromosome and therefore inherited together
Goes against Mendel’s Law of Independent Assortment
How do linked genes get “unlinked”?
Crossing Over
The frequency of crossing over between certain genes is used to make a chromosome map
Which two genes have the highest probability of crossing over? The lowest?
AB
C
ab
c
Highest: A & CLowest: A & B
Chromosome Map:Diagram of the linear order of genes on a chromosome
Sex Linkage Problems!!!!
Use these genotypic symbols for the sex linked trait of red-green color blindness in humans to solve the problems that follow.
"Normal" female = XBXB Carrier female = XBXb Color-blind female = XbXb Normal male = XBY Color-blind Male = XbY
1) A normal female marries a color blind male. What are the chances that the offspring will be color blind if they are females? What are the chances that the offspring will be color blind if they are males?
2) A color blind female marries a normal male. How many of the female offspring will be carriers of the color blind allele?
3) A man whose mother is color blind marries a woman with normal vision. What is the genotype of the husband? What percent of their offspring can be expected to be color blind? What percentage of their offspring can be expected to be carriers?
How do biologist keep track of inherited traits over generations in a family?
Pedigree (page 241)
Pedigree Key
Normal male
Affected male
Normal female
Affected female
Marriage
Dead
Let’s try a pedigree problem!
R = Tongue Roller r = No Tongue Roller
John Jones, a tongue roller, marries Jill Smith, a woman that cannot roll her tongue. John and Jill have four children that can each roll their tongue: John Jr., Alice, Lisa, and Sean. John Jr. later marries non-tongue roller Pamela, and they have four children: Jessica, Sherri, Mary, and John III. Sherri and Mary both can roll their tongues, and Jessica and John III are non-tongue rollers. Sean marries Robin, a non-tongue roller. Both Robin’s parents are non-tongue rollers also. Sean and Robin have four children: Nicholas, Harry, Donna, and Sean Jr. Nicholas, Harry and Donna each have the ability to roll their tongues. Sean Jr. cannot.
Human GeneticsSection 12.2
Human genetics is not as easy as Mendel’s peas!
Many patterns of inheritance
Human Patterns of Inheritance
1. Single allele trait2. Multiple allele trait3. Polygenic trait4. X-linked trait5. Nondisjunction
1. Single Allele Trait A trait that is controlled by a single
allele of a gene
Normal dominant-recessive (Mendel)
Example Genetic Disorders: Huntington’s Disease (autosomal
dominant) Cystic Fibrosis (autosomal recessive)
2. Multiple Allele Trait 3 or more alleles of the same gene
code for a single trait
Example: ABO Blood Type
IA = type A (dominant)IB = type B (dominant)i = type O (recessive)
Blood Type Problems If a person is type A blood….what is
his/her genotype?IAIA or IAi
If a person is type B blood….what is his/her genotype?
IBIB or IBi If a person is type O blood….what is
his/her genotype?ii
If a person is type AB blood….what is his/her genotype?
IAIB
Blood TypesBlood Type (Phenotype)
Genotype Can donate blood to: Can receive blood from:
O ii A,B,AB and O(universal donor)
O
AB IAIB AB A,B,AB and O(universal receiver)
A IAIA or IAi AB, A O,A
B IBIB or IBi AB,B O,B
Blood Type Problems # 1 A mother gives birth to a type O
child. The mother is type A blood. The two potential fathers are type A (father 1) and type AB (father 2).
Who’s the daddy?
Blood Type Problems #2 Pretend that Mark is homozygous for
blood type “A” allele, and Mary is type “O”.
What are all the possible blood types of their baby?
3. Polygenic Trait Trait that is controlled by 2 or more genes
Range of phenotypes Influenced by environmental factors too
Examples: skin coloreye colorhuman height
4. X-Linked Trait Trait controlled by a gene on the X
chromosome
Examples:colorblindness (recessive)hemophilia (recessive)
Hemophilia Pedigree
5. Nondisjunction The failure of chromosomes to
separate during meiosis resulting in one gamete with too many chromosomes and one gamete with too few chromosomes
Trisomy Monosomy
Trisomy: cell with 3 copies of a chromosome (too many chromosomes)
Monosomy: cell with 1 copy of a chromosome (too few chromosome)
Example Genetic Disorders:Down Syndrome (Tri-21)Klinefelter’s Syndrome (XXY)Turner’s Syndrome (X__)
Blood Typing Lab! BackgroundBlood is a tissue comprised of 4 components:
plasma, red and white blood cells, and platelets. Plasma is a clear straw-colored liquid portion that makes up 55% of the blood. It contains a number of blood-clotting chemicals that help stop bleeding. Red and white blood cells and platelets make up the remaining 45% of the blood. Red blood cells are tiny biconcave discs. Each red blood cell contains the oxygen-binding protein, hemoglobin. Hemoglobin contains 4 iron ions with bind with oxygen and carbon dioxide.
Blood functions principally as a vehicle with transports gases, metabolic waste products and hormones throughout the body. As blood passes through the lungs, oxygen molecules attach to the hemoglobin. As blood passes through the body’s tissues in capillary beds, the hemoglobin releases the oxygen. Carbon dioxide and other waste gases are, in turn, transported by the hemoglobin back to the lungs. Thereafter the process is repeated.
Mutations that Lead to Genetic Disorders:
Mutation: a change in the DNA of an organism
Can involve an entire chromosome or a single nucleotide
Can lead to genetic disorders
Mutation Types
1. Germ-cell mutation: occurs in the germ cells (gametes)
Does not affect the organism Does affect the organism’s offspring
2. Somatic-cell mutation: occurs in the organism’s body cells
Does affect the organism Does not affect the organism’s offspring
3. Lethal mutation: causes death, often before birth
4. Chromosome mutation: change in the structure of a chromosomea. Deletion – loss of a piece of chromosome b. Inversion- segments of chromosome breaks off, flips, and reattachesc. Translocation- piece of chromosome breaks off and attaches to another chromosomed. Nondisjunction- chromosome fails to separate during meiosis
Deletion Inversion
NondisjunctionTranslocation
5. Gene mutation: involves large segments of DNA or a single nucleotide of DNA
a. Point mutation: single nucleotide mutation within a codon (substitution, addition, or deletion)b. Frame shift mutation: cause the misreading of codons during translation thus making the wrong protein (insertion or deletion)
Detecting Human Genetic Disorders
Before Pregnancy:1. Genetic Screening2. Genetic Counseling
During Pregnancy:1. Amniocentesis2. Chorionic Villi Sampling
After Birth:1. Genetic Screeningvideo
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