Chapter 9: Sexual Reproduction and Inheritance

Sexual Reproduction

The combination of two genomes to form a single individual, shuffles the alleles present in a population creating new combinations

Origin of sexes is due to mitochondria

By having 2 copies of a genome, if one becomes damaged there is second copy preventing the cell from dying and taking the mitochondria with it

Free radicals

Made by mitochondria that cause cellular damage

Mutations

Any change to the sequence of DNA, creates new alleles in a population

Meiosis

Sexual reproduction in eukaryotes, there are 2 rounds of cell division, generates gametes

Meiosis 1

Important for generating genetic diversity, first round of cell division, sister chromatids form a tetrad which is when the homologous chromosomes become attached in a single structure, the daughter cells go from diploid to haploid

Meiosis 2

The sister chromatids are pulled apart and now each daughter cell only has one of each chromosome

Spermatogenesis

Formation of sperm, takes place in the testes, a self-generating stem cell replicates by mitosis forming the primary spermatocyte which remains a stem cell and the second primary spermatocyte undergoes meiosis 1 to form secondary spermatocyte which then undergoes meiosis 2 forming the 4 haploid daughter cells which them mature into sperm

Oogenesis

Formation of the egg, primary oocyte begins meiosis in the follicles prior to birth and takes place in the ovaries, beginning with puberty about every 28 days a primary oocyte will complete metaphase 1 forming a secondary oocyte which is then halted at meiosis 2 unless it is fertilized

Crossing Over

Takes place in prophase 1 of meiosis, the alleles on homologous chromosomes can switch places which breaks linked genes and creates new combinations of linked alleles

Random Orientation of Chromosomes

Occurs during metaphase 1, the orientation of chromosomes is random which results in different combinations of maternally and paternally inherited chromosomes

Random Fertilization

Random sperm is chosen to fertilize the egg

Who discovered the first principles of inheritance?

Mendel did with the experiment of pea plants which showed that each parent contributed a gene

Allele

Different versions of a gene

Homozygous

two copies of the same allele

Heterozygous

Having two different alleles for the same gene

Genotype

The genes in an organism

Phenotype

The outward appearance of an allele

Dominant

The allele will be expressed if there is one copy of it present

Recessive

Requires both copies to be expressed

Law of Independent Assortment

Genes are inherited independently of each other

Mendel’s Contribution

Showed that genes are passed from one generation to the next as discrete units, he disproved blending inheritance, and Mendelian Inheritance were the first rules of genetics

What did Thomas Hunt Morgan do?

He brought in the age of modern genetics and discovered mutations and linked genes which didn’t follow Mendel’s Independent Inheritance

Codominance

Both alleles are expressed

Incomplete Dominance

The heterozygotes have a phenotype in between both alleles

Pleiotropy

One gene affects several other traits

Epistasis

One gene controls the expression of another gene

Polygenic Trait

Two or more genes controls the expression of another gene

Phenotypic Plasticity

A trait changes in response to the environment