Unit 5 Vocabulary Asexual vs. Sexual Reproduction

Asexual reproduction

Reproduction in complex multicellular organisms

Sexual reproduction

Variation in offspring

Mitosis

Produces exact copies

Meiosis

Produces gametes (reproductive cells)

Haploid

Contain one copy of each chromosome

Diploid

Contain two copies of each chromosome

Interphase

DNA is replicated; The cell prepares for division

Meiosis 1

Homologous pairs are separated

Prophase 1

Homologous pairs can exchange segments during crossing over

Metaphase 1

Homologous pairs line up in the middle of the cell; Independent assortment - pairs randomly line up in the middle

Anaphase 1

Homologous pairs are separated (A)

Telophase 1

Two nuclei form and the cell splits into two

Crossing Over

Exchange of genetic material between homologous chromosomes

Tetrad

A group of four chromatids formed by synapsis at the start of meiosis

Sister chromatid

Replicated chromosomes, identical to each other

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 A

Telophase 2

Nuclei form and cells split

Spermatogenesis

Production of sperm cells

Oogenesis

Production of egg cells

Genetic Variation

Variation in population is an advantage; Sexual reproduction increases variation in populations

Nondisjunction

Problems with the meiotic spindle cause daughter cells to have too many or too few chromosomes

Deletion

A chromosomal segment is removed

Duplication

A chromosomal segment is repeated

Inversion

A chromosomal segment is reversed within a chromosome

Translocation

A chromosomal segment is moved from one chromosome to another nonhomologous one

Nondisjunction

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

Sister chromatids

The replicated chromosomes, no longer identical

Homologous chromosomes

Chromosomes that contain genes for the same trait and are the same size

Autosomal dominant

Trait is passed from generation to generation; Kids with the trait had to have a parent with the trait

Autosomal recessive

Trait can skip generations; Kids can have it even if their parents did not

Dominant allele

Codes for a functional protein; Masks the effect of the recessive allele

Recessive allele

Codes for a non-functional protein; Only expressed when there are two copies

Genotype

An organism's genetic makeup

Phenotype

Physical appearance of a trait

Test Cross

Crossing an organism with the dominant phenotype but an unknown genotype with a homozygous recessive organism to determine the unknown genotype

Law of segregation

During meiosis, alleles segregate (separate); Each allele for a trait is packaged into a separate gamete

Law of independent assortment

Different genes separate into gametes independently; Only true for genes on separate chromosomes or on same chromosome but far apart so that crossing over happens frequently

Pedigrees

Family tree diagrams that show the inheritance of traits

Incomplete Dominance

Heterozygotes show an intermediate phenotype

Co-dominance

Two alleles affect the phenotype in separate, distinguishable ways

Pleiotropy

Most genes are pleiotropic - 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

Sex-linked traits

Traits that are located on the sex chromosomes

Y linked

Very few traits; Traits only passed from father to son

X linked

Traits passed on the X chromosome; Males get their X from their mother; An x-linked trait is never passed from father to son

X-inactivation

One of the X chromosomes in female mammals becomes inactivated during embryonic development

Non-nuclear Inheritance

In animals, mitochondria are passed on through egg cells and not sperm cells; In plants, mitochondria and chloroplasts are passed on through ovules and not pollen grains