Lecture 2.1 - Genotype-Phenotype Meiosis and Mendelian Ratios

Meiosis

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

Diplontic

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

The haplontic life cycle is marked only by

mitosis in the haploid stage

Haplodiplontic organsisms undergo

mitosis in haploid and diploid stage

Is diplontic or haplontic organisms more stable?

Diplontic organisms are more stable because of homology-directed repair mechanisms during mitosis (can’t use during haploid mitosis in haplontic eukaryotes)

Asexual reproduction

mitosis creates two identical organsims from one individual

Sexual reproduction

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

• Mom makes he egg, Dad makes sperm, they combine to make you

Each gamete contains only…

half of the genetic material that the adult will have

What is not a stable species?

• Triploids are not stable since they can’t undergo meiosis properly

• 3 is not divisible by 2, you need a stable half ploidy to undergo meiosis

Prophase 1

Homologous chromosomes are held together with a protein lattice (containing the protein cohesin, which binds satellites on the chromosome)

Crossing over happens because

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

Crossing over 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

experience recombination

Parental chromosomes

chromosomes that don’t

What is the outcome of meiosis?

Creates haploid cells from a diploid cell progenerator

What did Mendel discover about peas?

• F1 phenotypes shoes dominance/recessive relationships

• F2 phenotypes shows the reoccurrence of recessive traits

What did Mendel discover about genes?

There are “hereditary determinants of particulate nature”

What did Mendel discover about homologous chromosomes?

Genes come in pairs

What did Mendel discover about dominant/recessive alleles/Law of Dominance?

Alternate phenotypes of a single character are determined by different forms of these genes

What did Mendel discover about ploidy?

Gametes contain one member of each gene pair

What did Mendel discover about the Law of Segregation?

Inheritance of alleles was random/Random fertilization

What did Mendel discover about Law of Independent Assortment?

Genes controlling different traits are inherited independently

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