Genetics Unit 1

Chapter 1-4

Genetics

the study of heredity and variation of inherited traits

Genome

a collection of all the genes on all chromosomes in an organism

Chromosome

single long molecule of double-stranded DNA that are bound by many different kinds of proteins

Homologous Pair

a set of two unreplicated chromosomes that carry alleles for the same genes in the same locations

Telomere

each end of a chromosome or chromatid

Locus

the position of a gene on a chromosome or chromatid

Centromere

the point of each chromosome or chromatid where each half joins

Arm of Chromosome

the space between the centromere and telomere

Haploid

one copy of the genome or chromosome (1n)

Diploid

two copies of the genome or chromosome (2n)

Tetraploid

four copies of the genome (4n)

Euploid

Chromosome number that is a multiple of n (normal cell)

Aneuploid

more or less than the expected number of chromosomes

C

the amount of DNA in a replicated haploid set

Chromatid

one half of a replicated chromosome

Sister Chromatids

one full replicated chromosome (attached at centromere)

Non-Sister Chromatids

chromatids from originally homologous pair of chromosomes

Gap Phase 1

active gene expression and cell activity, preparing for DNA synthesis

G1 Checkpoint

check for adequate cell size and nutrient availability

S Phase

DNA replication and chromosome duplication

S Checkpoint

check for complete replication and no matching errors

Gap Phase 2 / Interphase

Preparation for cell division

G2 Checkpoint

check for good cell size and complete replication

Prophase

chromosome condensation begins, paired centrosomes begin to migrate to ends of cell, and nucleolus disappears

Metaphase

chromosomes are fully aligned in center of cell along plate and each chromatid is attached to kinetochore microtubule from the centromere

Anaphase

sister chromatids are pulled apart to opposite poles

Telophase

cell elongates and nuclear envelope reassembles with new chromosomes

Cytokinesis

division of cytoplasm to form new cell

Kinetocore Microtubules

small fibers embedded in kintecore that assembles at centromere and is responsible for chromosome movement during cell division

Nonkinetocore Microtubules

fibers that extend toward each other form two polar centrosomes and overlap to elongate/stabilize during cell division

Astral Microtubules

fibers that grow toward the cell membrane where they attach to stabilize cell

Cyclin

a protein that affects when each phase of the cell cycle is active

Cyclin Dependent Protein Kinases

enzymes that are present at constant levels until their specific cyclin activates them for their phase (inactive until binding)

Prophase 1: Lepotene

progressive chromosome condensation begins and centrosomes start to migrate toward opposite poles

Prophase 1: Zygotene

homologous chromosomes enter synapsis, mitotic spindles form, and nuclear envelope breakdown begins

Prophase 1: Pachytene

synapsed homologous chromosomes are seen as bivalent structures and crossing over occurs in non-sister chromatids while kinetocore microtubules attach to kinetochore

Prophase 1: Diplotene

crossing over is complete and synaptonemal complex dissolves which leaves the chiasmata to hold sister chromatids together, tetrads are visible, and the nuclear envelope breakdown finishes

Prophase 1: Diakinesis

completion of end of synapsis and tetrads are moved toward middle of cell

Chromosomal Theory fo Inheritance

chromosomes are in pairs with one from mother and one from mother, chromosomes are separated and independently assorted to gametes, and parental vs recombinant type is decided during gamete formation

Hemizygous

half-zygous, used to describe males with x-linked genes

Nondisjunction

failed chromosome separation

SRY Gene

sex determining region of Y chromosomes that determines genitalia in mammals

Pseudoautonomal Regions

regions on the telomeres that act like autosomal traits even though they are on the sex chromosomes

X-Inactivation

long non-coding pieces of RNA that will completely coat one of the X chromosomes very early in embryogenesis

Barr Bodies

randomly inactive X chromosomes

Haplosufficient

one copy is sufficient to produce phenotype

Haploinsufficient

single copy not enough to produce phenotype

Loss of Function Mutation

mutation causing significant decrease or complete loss of functional gene activity

Null/Amorphic Mutation

mutation causing complete loss of gene function (homozygous produce zero product and heterozygous produces some product)

Leaky Mutation

mutation causing partial loss of gene function (still produces small amount of wild type gene product)

Dominant Negative Mutations

mutations that cause dominant mutant phenotypes by causing abnormal interactions with other genes

Gain of Function Mutations

mutations that result in gain of new function

Hypermorphic Mutations

mutations that cause more gene activity per allele (gene product is typically same as wild type, just in greater amounts)

Neomorphic Mutations

mutations with new gene activities not found in wild type

Incomplete/Partial Dominance

when the heterozygous phenotype falls in a spectrum between homozygous dominant and homozygous recessive

Codominance

when heterozygous produces unique phenotype but each allele expression is distinguishable (often in clusters or speckles)

Allelic Series

a way of writing the relationship between multiple alleles for the same gene in order to show relative dominance

Incomplete Penetrance

a genotype fails to display the matching phenotype

Pentrant

a genotype that displays its matching phenotypes

Variable Expressivity

the degree or form of phenotypic expression

Pleiotropy

alteration of multiple features of a phenotype as a result of one mutation

Anabolic Pathways

pathways that produce series of intermediate compounds by building

Catabolic Pathways

pathways that breakdown things into a series of intermediate compounds

Prototrophic

wild type

Auxotrophic

mutant type

Genetic Dissection

an experimental approach that separately tests the ability of a mutant to execute each step of a pathway by determining the point at which the pathway is blocked in each mutant

Epistasis

when one gene affects the genotypic expression of another gene of the same phenotype

Complementary Gene Interactions

type of epistasis when genes must interact in tandem to produce certain phenotype (9:7 ratio)

Duplicate Gene Action

epistasis that allows dominant alleles of either duplicate gene to produce the wild type phenotype (15:1)

Dominant Gene Interactions

epistasis where there is one phenotype if dominant alleles are present at each gene, one phenotype if recessive alleles are homozygous at either gene, and one phenotype if both genes are homozygous recessive (9:6:1)

Recessive Epistasis

epistasis when recessive alleles at one gene mask or reduce expression of alleles at interacting locus (9:3:4)

Dominant Epistasis

epistasis where a dominant allele of one gene masks or reduces expression of the second gene (12:3:1)

Dominant Supression

epistasis when one dominant allele of one gene suppresses expression of alleles of second gene (13:3)