Genotype-Phenotype Meiosis and Mendelian Ratios

Meiosis

• special form of cell division that creates gametes (sex cells), like eggs and sperm

• occurs in the nucleus of somatic cells

Life cycles

• when meiosis and mitosis occur

• adults undergo meiosis to create single sperm/egg which interact to form a zygote,

• which in turn undergoes mitosis until it develops into an adult to restart the process

• Meiosis is “gametic”

Diplontic

• mitosis occurs only in the diploid stage, not the haploid stage (sperm/eggs)

• can utilize their extra copy to repair double strand breaks during mitosis

• leading to more stable karyotypes and fewer wasted resources due to dead end haploid individuals

haplontic life cycle

• the only diploid cell is the zygote, which immediately undergoes meiosis, and mitosis is only for haploid cells

• there are two routes for the generation of novel gametes, either mitosis only, or fertilization + meiosis which generates genetic diversity

• Meiosis is “zygotic”

Haplodiplontic organisms

• experience mitosis in both haploid and diploid cells

• can repair structural mutations only if the majority is their mitosis is in the diploid stage

Haplontic cells

• advantage that they do not need to sexually mate

• [blank] cells can divide mitotically in the haploid state in the short term, while occasional mating still provides enough genetic diversity to be an advantage

Asexual

• Mitosis creates two identical organisms from one individual

• Not capable of forming a long, stable life

Sexual

• Meiosis in different individuals in a population create gametes which combine to make a new organism

• enough genetic diversity to escape diseases

Ploidy

is determined by number of chromosomes of each type a cell has

Triploids

• are not stable species since they cannot undergo meiosis properly

• 3 is not divisible by two ( need a stable half ploidy to undergo meiosis)

Diploid

Cells with two copies of each chromosome

Haploid

Cells with one copy of each chromosome

heterozygous genotype

individuals with the [blank] as “carriers” because they “carry” the recessive allele but don’t show that phenotype

homozygous genotype

phenotype that comes from a recessive allele

Prophase 1

Homologous chromosomes are held together with a protein lattice

Crossing Over

• have similar DNA sequences, homologous chromosomes exchange part of their DNA during Meiosis 1

• This process also serves as a checkpoint to make sure each chromosome is paired up before the chromosomes divide

• This is when many tumor suppressor genes are active in the cell cycle

Recombinant chromosomes

Chromosomes that experience recombination

Parental chromosomes

Chromosomes that don’t experience recombination

Mendels’s Laws of Heredity

Law of Dominance: some alleles are dominant, others are recessive, a heterozygous individual will display the dominant form
Law of Segregation: only 1 allele is carried in a gamete
Law of Independent Assortment: genes of different traits segregate independently to the gametes