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