Chapter 9 - Sexual Reproduction and Inheritance

Meiosis

Sexual reproduction that has 2 rounds of cell division and turns diploid gametes into haploid gametes.

Sexual Reproduction

Combination of two genomes to form a single individual

Theory 1 of Origin of Sexual Reproduction

Mitochondria did it due to the creation of oxygen reactive species.

Theory 2 of Origin of Sexual Reproduction

More genetic variation in populations because it's the shuffling of alleles to in a population to create new combinations. 

Theory 3 of Origin of Sexual Reproduction

Removes bad versions of genes from a population.

Meiosis 1 

Daughter cells become haploid, sister chromatids form tetrad which is pulled apart, cells are haploid because they no longer contain two copies of the genes.

Meiosis 2

Sister chromatids are pulled apart and daughter cells now only have one of each chromosome.

Spermatogenesis 

Formation of male gametes.

Oogenesis

Formation of female gametes.

Non-disjunction

Unequal separation of chromosomes leading to extra or reduced chromosome number.

Crossing Over

Important for genetic diversity happens when tetrads are formed and alleles on homologous chromosomes switch places.

Random Orientation of Chromosomes

Different combinations of maternally and paternally inherited chromosomes (calculation 2^n)

Random Fertilization 

Egg releases chemicals which attract sperm and might be able to decide which sperm fertalizes. 

Gene

Heritable feature.

Allele

Different versions of a gene.

Homozygous

Two copies of the same allele, true bred

Heterozygous 

Two different alleles for the same gene

Genotype

Actual gene in an organism

Phenotype

The outward appearance of expressed genes

Dominant

Allele will be expressed 

Recessive

Requires both copies to be expressed

Law of Independent Assortment

Some genes are inherited independently from each other (they need to be on different chromosomes)

Mendelian Inheritance

• One gene, two alleles

• One copy from each parent

• An allele can be dominant or recessive

Particular Inheritance

Genes are passed from one generation to the next as discrete units (disproved blended inheritance)