Meiosis and Inheritance Flashcards

Asexual Reproduction

Mitosis

Produces exact copies

Single-celled eukaryotes

Simple multicellular eukaryotes

Sexual Reproduction

Reproduction in complex multicellular organisms

Variation in offspring

Reproductive cells are produced by meiosis

Meiosis

Produces gametes (reproductive cells)

Two cell divisions

Reduces the number of chromosomes by half

Diploid (containing 2 copies of each chromosome) → haploid (containing one copy of each chromosome)

The cells that are produced are different from each other and from the original cell

Interphase

DNA is replicated

The cell prepares for division

Interphase only happens once

Prophase 1

Homologous pairs can exchange segments during crossing over

Metaphase 1

Homologous pairs line up in the middle of the cell

Independent assortment

Independent Assortment

Pairs randomly line up in the middle

• during metaphase I of meiosis results in the formation of gametes that are different from each other (2²³ combinations in gametes

Anaphase 1

Homologous pairs are separated

Telophase 1

Two nuclei form and the cell splits into two (haploid)

Meiosis 2

Sister chromatids are separated

Prophase 2

Crossing over does not occur

Metaphase 2

Chromosomes line up in the middle of the cell

Anaphase 2

Sister chromatids are separated

Telophase 2

Nuclei form and cells split (haploid)

Crossing Over

Mixes alleles across homologous chromosomes, creating new combinations of traits on each chromosome

Random Fertilization

of an egg cell (any two parents will produce a zygote with 223 x 223 possible diploid combinations)

Autosomes

44 non-sex chromosomes.

Nondisjunction

chromosomes don’t separate properly during meiosis

Results in zygotes with 3 copies of a chromosome (trisomy) or 1 copy (monosomy) instead of 2 copies of each chromosome

Breaking of chromosomes

Deletion

Duplication

Inversion

Translocation

Deletion

A deletion removes a chromosomal segment.

Duplication

A duplication repeats a segment

Inversion

An inversion reverses a segment within a chromosome

Translocation

moves a segment from one chromosome to another, nonhomologous one.

Phenotype

physical appearance of a trait

Genotype

an organism’s genetic makeup

Law of Segregation

During meiosis, alleles segregate (separate)

Homologous chromosomes separate during anaphase I

Each allele for a trait is packaged into a separate gamete

Law of Independent Assortment

Different genes separate into gametes independently

Non-homologous chromosomes align independently during metaphase I

Only true for genes on separate chromosomes or on same chromosome but far apart so that crossing over happens frequently

Incomplete Dominance

Heterozygotes show an intermediate phenotype

red, pink, white

Co-Dominance

2 alleles affect the phenotype in separate, distinguishable ways

Pleiotropy

affect more than one phenotypic character

Epistasis

One gene masks another

Polygenic Inheritance

Some phenotypes are determined by the additive effects of 2 or more genes on a single character

Phenotypic Plasticity

Phenotype is controlled by the environment and genes