Topic 3: Genetics (3.1-3.3)

gene

a heritable factor that consists of a length of DNA and influences a specific trait

DNA

deoxyribonucleic acid; a genetic blueprint coding for and determining the characteristics of an organism

locus

the position of a gene on a particular chromosome

alleles

various specific forms of a gene/specific trait; differ from each other by one or only a few bases

explain how new alleles are formed

through mutations

gene mutation

a change in the nucleotide sequence of a section of DNA for a specific trait

point mutation

a single nucleotide change; results in a codon that codes for a different amino acid from the original codon; can be neutral, beneficial, or detrimental

neutral mutations

have no effect on the function of the feature

beneficial mutations

change the gene sequence to create variance

detrimental mutations

disrupt the normal function of a trait

missense mutation

a point mutation in which a single nucleotide changes

nonsense mutation

a genetic mutation in a DNA sequence that results in a shorter, unfinished, protein product

genome

total genetic information of a cell, organism, or organelle

state how many chromosomes the human genome consists of

46 chromosomes, 23 pairs

proteome

the entire set of proteins that can be expressed by a genome, cell, tissue, or organism; in cells genome is the same but the proteome is different

single nucleotide polymorphism (SNP)

a variation in a single nucleotide that occurs at a specific position in the genome

list characteristics of prokaryote genetics

1. prokaryotes have no nucleus, DNA is not enclosed

2. prokaryote DNA is not packaged (naked)

3. DNA floats freely in the nucleoid

4. genophore: single chromosome of a circular DNA molecule

plasmids

circular DNA molecules; NOT present in eukaryotes and only SOMETIMES present in prokaryotes; can be exchanged through pili

list characteristics of eukaryote genetics

1. use of histone proteins compact DNA greatly for storage

2. DNA is contained in the nucleus

centromere

a constriction point on chromosomes which divides the chromosome into two sections

homologous chromosomes

• carry the same sequence of genes but not the same alleles

• inherited from parents in sexually reproducing organisms

• same structural features

• diploid

diploid cells

• pairs of homologous chromosomes

• possess two gene copies (alleles) for each trait

• all body cells are diploid and new ones are created by mitosis

haploid cells

• one chromosome of each pair

• all gametes are haploid, made from diploid cells through meiosis

outline how the formation of a new organism involves diploid and haploid cells

diploid organisms create gametes (sex cells) during reproduction with half the number of chromosomes (haploid); then two haploid gametes fuse to create a zygote

explain how sex is determined by the sex chromosomes

• females carry two copies of the X chromosome XX

• males carry one copy of the X chromosome and one copy of the Y chromosome XY

• the Y chromosome carries the genes for male sex characteristics

• homologous in women but not in men

• always determined by the male

karyotypes

the number and types of chromosomes in a eukaryotic cells

karyograms

a photo or diagram showing the chromosomes of an organism in homologous pairs by decreasing length

meiosis

reduction division; a diploid nucleus divides into four haploid cells

prophase I

• chromosomes condense

• nuclear membrane dissolves

• chromosomes pair forming bivalents

• crossing over occurs

• homologous chromosomes are held together at points called chiasmata

metaphase I

• spindle fiber from centrioles connect to bivalents pulling them toward the middle of the cell

anaphase I

• spindle fibers contract splitting the bivalent

• homologous chromosomes move to opposite poles of the cell

telophase I

• chromosomes decondensed

• nuclear membrane may reform

• cell divides, cytokinesis

• ends with two haploid daughter cells

prophase II

• chromosomes condense, nuclear membrane dissolves, centrioles move to opposite poles

metaphase II

• spindle fiber from centrioles connect to bivalents pulling them toward the middle of the cell

anaphase II

• spindle fibers separate the sister chromatids, now called chromosomes

telophase II

• chromosomes decondensed

• nuclear membrane may reform

• cell divides, cytokinesis

• ends with four haploid daughter cells

nondisjunction

a failure of homologous chromosomes or sister chromatids to separate properly during cell division; three forms:

1. failure of a pair of homologous chromosomes in anaphase I

2. failure of sister chromatids to separate during meiosis II

3. failure of sister chromatids to separate during mitosis