Mendelian genetics & Cytogenetics

Who discovered the fundamental laws of inheritance through studying peas?

Gregor Mendel: His experiment with peas plants presented the appearance of genes in the offspring resulted in phenotypes that were dominant or recessive.

Know as the “father of genetics”

What are the 3 principles or laws of inheritance Mendel found?

1. Law of dominance

2. Law of segregation

3. Law of independent assortment

Homozygous

Same allele of gene 1 on both homologoues (aa, AA)

-Dominant: AA

-Recessive: aa

Heterozygous

Different alleles of gene 2 and gene 3 on each homologue

-Aa

Genotype

Describes the alleles example (Aa, AA, aa)

-This will then determine the phenotype

Phenotype

Is the trait, example: short, tall, brown, white

Law of Dominance

When an organism is heterozygous for a trait it expresses only the dominant allele. The recessive trait will be express only when the offspring inherits the recessive allele from both parents.

Law of Segregation

Sperm and egg carry 1 allele for each trait due to meiosis I & II of anaphase

When they reproduce their offspring will have 2 alleles

Law of Independence

independent assortment, alleles get sorted into gametes

Punnett square

A tool to show all possible allelic combinations of gametes in a cross of parents with known genotypes to predict the probability of their offspring having certain phenotypes.

Monohybrid

Genetic cross in which a single trait is followed from one generation to the next.

Incomplete Dominance

Occurs when neither of the two alleles is fully dominant nor recessive towards each other.

-This results in a third phenotype

example: red and white flower produce offspring who comes out pink

Co-dominance

When both alleles are dominant and equally expressed.

-The colors don’t blend but are equally seen

example: cattle coat (red, white, roan)

Polygenic inheritance

The inheritance of traits that are determined by more than one gene.

This has many possible phenotypes

example: skin color

Cytogenetics

A field of study which analyzes the number and structure of human chromosomes.

-Being able to analyze the number and structure of chromosomes in a cell can help identify genetic problems as the cause of disease or disorder.

How do chromosomal abnormalities occur?

-During cell division

-Most occur by accident in the production of gametes during meiosis

-Some happen after conception in the embryonic development during mitosis

Cytogenetic analysis

is performed during pregnancy if the fetus is showing developmental delays.

-It can determine if there is an extra or missing chromosome (aneuplodies) or structural abnormalities (deletions, duplications, translocations)

Centromere

-When the chromosome replicates, it keeps the sister chromatids together until they get pulled apart in anaphase.

-spindle fibers attach

-gives chromosome its characteristic shape (each has 1)

Metacentric chromosome

a chromosome with a centromere located in the middle of the chromosome, separating the two arms.

Submetacentric chromosome

Has a center mere that is slightly displaced from the center, resulting in one short arm and one long arm

Acrocentric chromosome

A chromosome whose centromere is placed very near one end

-p(short) & q(long) arms

What are the 3 key features to identify chromosomes

1. Size

2. Banding Pattern

3. Centromere position

Banding pattern

There is a unique patter of light and dark ands for each chromosome

Polyploidy

3N=69

-Increases to three sets of chromosomes that are called Triploidy

Aneuploidy

2n-1

-one member of the chromosome pair is missing

-Caused by non-disjunction

Non-disjunction

The failure of homologous chromosomes (meiosis I) or sister chromatids (meiosis II) to separate properly during meiosis in anaphase