Patterns of Inheritance- Mendelian Genetics- June 16 - PART 1

the study of DNA, its structure, its mutations, and hereditary variations in DNA

Genetics

• An Austrian monk

• “Father of Modern Genetics”

• He took care of the monastery gardens

• He studied traits in flowering plants

  • Pea plants were his primary organism of study

Gregor Mendel

every organism produced through sexual reproduction has how much % of its genetic information from each parent?

50%

a unit of information

• a piece of DNA on a chromosome that codes for a specific trait

• each individual typically has two blank for each trat

• one from each parent

gene

the exact position a gene is found on a chromosome

Locus

different forms of the same gene

• ex: flower color

alleles

2 identical alleles in a given gene

• ex: 2 purple alleles or 2 white alleles

Homozygous

2 different alleles in a given pair

• ex: one purple allele and one white allele

heterozygous

the allele that is expressed in a heterozygous individual

• represented by a capital letter

• pea plants A= purple

dominant allele

what traits did mendel study

flower color

-flower position

-seed color and seed shape

-pod shape and pod color

-stem length or height

the allele that is not expressed or is masked in a heterozygous individual

• represented by a lower case letter

• pea plants, a=white

recessive allele

the actual genetic makeup that an individual has for a trait

genotype

two dominant alleles in a given gene pair

• AA

homozygous dominant

two recessive alleles in a given pair

• aa

homozygous recessive

two different alleles (one dominant one recessive) in a given gene pair

• Aa*

heterozygous*

the actual physical or physiological expression of a gene pair

phenotype

an individual that is homozygous dominant or heterozygous would have a phenotype of what flowers

purple flowers

an individual that is homozygous recessive would have the phenotype of what flowers

white flowers

a. complete (true) dominance

b. incomplete dominance

c. multiple alleles

types of inheritance

• 2 possible alleles exist for a trait

• 1 is dominant, 1 is recessive

• Heterozygous individuals express the dominant form of the trait

Complete (true) dominance

• 2 possible alleles exist for a trait

• no dominance exists

• heterozygous individuals express both alleles simultaneously—> results in a 3rd phenotype

Incomplete dominance

• more than 2 possible alleles exist for a trait

• multiple phenotypes possible

multiple phenotypes possible

A cross (mating) between 2 parents resulting in offspring

• monohybrid

• dihybrid

Genetic cross

a genetic cross involving the inheritance of one trait (4 box punnett square)

monohybrid cross

a genetic cross involving the inheritance of two traits simultaneously (16 box punnett square)

Dihydrid Cross

P generation

parental generation (parents)

F1 generation

• 1st generation of offspring from parents

first filial generation

F2 generation

• 2nd generation of offspring from F1 parents

second filial generation

a diagramming method used to study the inheritance of a trait by offspring from two known parents

Punnett Square

punnet squares predict what

offspring will results from 2 known parents

traits carried on autosomes (non sex chromosomes)

• in humans, some disorders are recessive, while others are dominant

autosomal inheritance

traits carried on sex hormones

• in humans, most disorders are recessive, few are dominant

sex-linked inheritance

• Albinism

• Cystic fibrosis

• Galactosemia

• Phenylketonuria

• Sickle Cell Disease

• Tay Sach’s Disease

examples of autosomal recessive disorders

autosomal recessive disorders

A=

a=

=normal

= disorder

to express disorders that are recessive, an individual would need to have a

homozygous recessive genotype

autosomal disorder that results in a lack of skin pigmentation due to low or absent melanin production

albinism

autosomal recessive disorder that is the most common lethal genetic disorder in the U.S.  It results in an over secretion of mucus that clogs the respiratory tract and can lead to fatal respiratory infections

cystic fibrosis

autosomal recessive disorder that results from an abnormality or lack of liver enzymes needed to transform galactose to glucose. 

• Galactose accumulates in the blood and leads to mental defects.

galactosemia

autosomal recessive disorder that results from a lack of enzymes that transform the amino acid, phenylalanine to tyrosine. 

• Phenylalanine accumulates in the blood and becomes a neurotoxin. 

• Special diets, containing protein without phenylalanine, are required for individuals with this disorder.

phenylketonuria (PKU)

autosomal recessive disorder that results when a substitution of one amino acid occurs in the amino acid sequence of hemoglobin. 

• This causes red blood cells to “sickle” thereby impairing oxygen transport in the blood. 

• Most common in individuals of African descent.

sickle-cell disease

autosomal recessive disorder that results from a deficiency of a lysosomal enzymes that is needed to break down glycolipids (carbohydrates) on the surface of nerve cells. 

• The glycolipids clutter the nerve cell surface and interfere with nerve cell functioning. 

• This causes nerve impulses to be slowed. 

• Most common in individuals of Eastern European Orthodox Jewish descent.

Tay-Sach’s Disease

autosomal dominant disorders key

A= disorder

a= normal

autosomal dominant disorder that is a type of dwarfism that results due to defective cartilage and bone growth

Anchondroplasia

autosomal dominant disorder that causes a build up of a lactic acid in the brain which typically affects areas of the brain controlling skeletal muscle contractions and can result in jerky, abrupt movements, stuttering, dementia, and even death

huntington’s disease

autosomal dominat disorder that results in the development of extra digits on an individual’s hands and feet

polydactyly

to have a autosomal recessive disorder you must have the genotype of

aa, homozygous recessive

traits carried on sex chromosomes (that determine gender)

sex-linked inheritance

traits carries on X chromosomes only

• Females have 2 X chromosomes and therefore 2 genes for the trait

  • Homozygous dominant, homozygous recessive or heterozygous

  • Heterozygous females are carriers

• Males have 1 X chromosome and therefore only 1 gene for the trait

  • Males have a greater frequency of expressing sex-linked recessive disorders

X-linked chromosomes

most sex-linked disorders are

recessive

sex-linked disorders key

A= normal , a= disorder

only females with an XaXa genotype and males with an XaY genotype will express a

sex-linked recessive disorder

sex-linked recessive disorder that results in the inability to see color. 

• This is caused by the inactivation of some color receptors called cones which are located on the retina of the eye.

colorblindness

sex-linked recessive disorder that is a one type of early hair loss. 

• It results when enzymes that allow for the production of testosterone stop functioning and then prevents new hair growth and causes the loss of existing hair from their follicles

male-pattern baldness

a sex-linked recessive disorder that is a blood disorder where individuals lack the blood clotting mechanism. 

• It can be treated with medication. 

• If untreated, an individual could bleed out from a simple cut.

hemophilia

a sex-linked recessive disorder is the most common form of muscular dystrophy where an important protein in muscle tissue is absent. 

• It leads to the destruction of muscle tissue starting in the limbs and moving upwards. 

• The destroyed muscle tissue is then replaced by fat and connective tissue. 

• Respiratory failure occurs in individuals in their early to late 20’s.

duchenne’s muscular dystrophy

what chromosome is much larger in the human and carries more genes

the X chromosome

what chromosome only carries genes associated with being male

• the presence of it determines that an individual is biologically male

• the absence of it determines that an individual is biologically female

The Y chromosome

a human male will pass how many autosomes and what kind of chromosome to offspring via sperm

22 autosome and either an X or a Y chromosome

a human female will pass how many autosomes and what chromosome to offspring via her egg

22 autosomes and an X chromosome

the gender of a child is determined by

which sex chromosome is contained with the sperm cell