What is Genetics?

The study of how traits are inherited.

Heredity: The passing of traits from one generation to the next.

Traits: Characteristics

How can we determine the frequency of a trait in offspring?

Gregor Mendel: Father of Genetics.Discovered the basics of heredity

Mendel worked with Pea Plants

He concluded that each trait is controlled by "Two Factors" (genes), one from each parent.

Genes are short sections of chromosomes

(They control which traits are expressed in an organism)

Alleles : different forms of a gene that exist in a population.Some alleles can be dominant over other alleles

Mendel Law of Dominance:

When organisms pure for a trait are crossed, all their offspring will show the dominant trait.

The trait that was expressed is dominant, while the trait that did not show up was called recessive

Parent generation F1 Generation

Tall x Short all plants are Tall

Recessive:

  • A trait that is covered over.
  • Hidden when the other copy of the gene contains the dominant allele.
  • It shows up only when there is no dominant allele present
  • lower-case letter (t)

Dominant

  • A trait that covers over another form of that trait
  • Always shows up
  • capital letter (T)

Phenotype: The physical appearance of an organism

Genotype: The genetic makeup of an organism

Phenotype is: Brown hair

Genotype can be: Bb or BB

B: Brown

b: blond

For a recessive trait to show their appearance in an offspring, both recessive alleles must be present in an individual

Blond genotype is bb

Tall Plant (TT) x short plant (tt)

All offspring are Tall Plants (Tt)

Homozygous or pure; alleles for a trait are the same Ex: TT ortt

Heterozygous (hybrid): alleles for a trait are different Ex: Tt

  • Cross the F1 generation to itself.
  • F2 ¼ are short , ¾ are tall.

Punnet Squares:a technique used to help determine the possible frequency of a trait in offspring

Example: Pea Plant TT X Pea Plant tt

Let T= Tall allele (gene)

Let t= short allele (gene)

What is the phenotype of all the offspring?

What is the genotype of all the offspring?

Incomplete Dominance:

  • When neither allele for a gene follows the dominant/recessive pattern
  • The organism shows a trait that is an intermediate phenotype.

Example:

The gene for the color of some flowers has one allele for red and one for white. When both alleles are present, neither is dominant, and the flower color is pink. Cross: WW x RR all F1 will be WR(Pink)

Polygenic Inheritance

  • Occurs when a group of gene pairs acts together to produce a trait
  • The effects of many alleles produces a wide variety of phenotypes
  • Ex: eye color, height, and skin color are produced by a combination of many genes.

The impact of the environment on genes

The environment affects the expression of genes.

Ex: Himalayan rabbits: the dark-colored fur allele is able to express only at low temp.

Multiple Alleles:

  • A trait that is controlled by more than two alleles is said to be controlled by multiple alleles
  • Traits controlled by multiple alleles produce more than three phenotypes of that trait
  • Example:
  • The alleles for blood types in humans are:
  • A, B, and O
  • The O allele is recessive to both the A and B alleles

Genotype / Phenotype
AA or Ao / A
BB or Bo / B
AB / AB
oo / O

Sex Determination

Sex Linked Inheritance

There are more colorblind males than females?

There are more male hemophiliacs than female?

There are more males with muscular dystrophy than females?

Recessive traits that are carried on the X chromosome, only need one copy in males to express themselves.

Males (XY)

Females have two X chromosomes and therefore both must carry the recessive allele to be expressed

Female (XX)

Do these crosses using the Punnet Square for color blindness

Cross: XY(normal male) x XXc female carrier for color blindness

1) Colorblind male x Normal female

Xc Y XX

2) Colorblind male x Female carrier

Xc Y Xc X

3) Normal Male x Colorblind female

X Y XcXc

RECESSIVE GENETIC DISORDERS

Sickle Cell Anemia: abnormally shaped red blood cells that can not function properly. Oxygen can not reach tissues.

Cystic Fibrosis:Homozygous recessive disorder. Thick mucus builds up in the lungs and makes it hard to breath

Human Genome

  • Identify genes responsible for specific traits
  • Be able to begin treatment of disorders while children are young and save lives of people at risk.

Why do we study Pedigrees? See packet

  • Karyotyping: Enlarged photograph of the pair chromosomes undergoing mitosis. Show missing or extra chromosomes.

HUMAN GENOME

Tracking human genes:

Chromosome map representing all of the human genetic material or chart that shows the location of individual genes on a chromosome

  • Identify genes responsible for specific traits
  • Be able to begin treatment of disorders while children are young and save lives of people at risk.

Why would such gene map be useful?

  • More than 3000 human disorders are inherited: cancer, huntington's disease, cystic fibrosis etc...
  • Developing a map of these genes is the first step towards diagnosing