BIOL1020 MOD4 WEEK2

What is a gene and allele?

Gene:

• a hereditary unit of DNA

• Genes code for proteins, and proteins make traits

Allele:

• An allele is a variant of a gene

• Every gene has (at least) TWO alleles. Inherited from each parent

What are the Three laws of Mendelian Genetics?

1. Law of Dominance

2. Law of segregation

3. Law of independent assortment

What is the law of dominance

The dominant allele determines the organism’s appearance, whereas the recessive allele has no noticeable effect.

• Homozygous dominant - AA

• Heterozygous - Aa

• Homozygous recessive - aa

What is the Law of Segregatiion

Two alleles for a heritable characteristic segregate/separate from each other during gamete formation and end up in different gametes.

• segregation of alleles happens during anaphase I of meiosis I

What is the law of independent assortment

Two or more genes assort independently during gamete formation in metaphase I of meiosis I (when pairs of duplicated chromosomes line up at metaphase plate)

What is a test cross

Used to identify the genotype of an unknown parent by crossing with a known homozygous recessive organism.

How to set up dihybrid cross

How are the Laws on Mendelian Genetics Broken?

Law of Dominance broken by:

• Codominance

• Incomplete dominance

• Peristalsis

• Pleiotropy

Law of segregation broken by:

• “The ploidys” (chromosome non-disjunction)

Law of independent assortment broken by:

• Linkage

• Asymmetric inheritance

• Species-specific selection

Explain how the law of dominance is broken

Codominance and incomplete dominance

• some alleles are both expressed, giving heterozygous individuals unique expressions. Can be expressed as a mixing of traits (incomplete dominance) or 50-50 expression of original traits (co-dominance)

Epistasis

• Some genes can interfere with the expression of other genes. This can prevent or alter how a specific gene is expressed.

Pleiotropy

• a single gene can be responsible for a multitude of effects on trait expressions across the whole body.

Explain how the law of segregation is broken

Aneuploidy

• when alleles fail to segregate properly during meiosis I, leading to incorrect numbers of chromosomes in gametes.

Which can cause polyploidy

• having more than two copies of chromosomes or partial chromosomes

• Can cause a number of chromosomal disorders

Which can also cause monosomy

• if daughter cells have too many chromosomes, others are missing some.

• Only full monosomy in humans is turner syndrome.

How is the law of independent assortment broken?

Via Asymmetric inheritance

1. Species-species selection

2. Sex-linked traits (important one)

What are sex-linked traits?

Genes that are located on the X and Y chromosomes, their expression of genes is determined by sex.

Have different inheritance patterns which depend on t he sex of the parent providing the trait.