Unit 1 Genetics Test Review

Chromosome

a single piece of coiled DNA containing many genes

How Chromosomes Form

a single length of DNA is wrapped many times around histones, and forms nucleosomes

nucleosomes then coil up tightly to create chromatin loops

chromatin loops are then wrapped around each other

Diploid

a pair of each type of chromosome

one pair derived from ovum and the other from the sperm

Haploid

only one copy of every chromosome

n=23

Genes

basic unit of heredity in a living organism

holds information to build and maintain an organism’s cells and pass traits to offspring

a segment of a chromosome that contains the code of a single protein (enzyme). Enzyme then causes a chemical reaction to allow the traits to be shown/expressed

Allele

variation of a gene located at a specific location on a chromosome. Each individual organism has two ______ for each trait, which may be homozygous or heterozygous. _______ are alternate forms of a gene.

Homologous Chromosomes

chromosomes that are paired

are alike with regard to size and position of centromere

have the same genes, but not the same alleles at the same locus or location

Tetrad

pair of homologous chromosomes

chromatids of homologous chromosomes are aligned lengthwise, so that genes of one are adjacent to corresponding genes on the other (total of 4 chromatids)

Synapsis

formation of tetrad

Gamete

specialized sex cell (egg or sperm) that is haploid.

only has half the number of chromosomes

male and female gamete fuse and produce a diploid zygote which develops into a new individual

inheritance

passing genetic information from parent to offspring

Sex Chromosomes

1 pair out of 23 (X & Y) determining individuals sez

Female = XX

Male = XY

Autosomes/Somatic Chromosome

22 pairs out of 23, where it is all chromosomes by sex cells, and it is paired based on similar characteristics

Karyotype

photograph of a particular set of chromosomes for an individual (from largest to smallest & then sex chromosomes)

How are Karyotypes prepared?

a sample of a cell in metaphase is takes, then chromosomes are stained revealing banding patter, and then sorted and paired after

DNA

contains instructions for making proteins within the cell

Double Helix

basic shape of DNA, a double-stranded molecule made of two very long polymers bonded together

Polymer

long molecule made of repeating subunits of monomers (one DNA strand is made of millions of monomers of nucleotides)

Monomer

atoms bonded together to create a larger molecule. many bond together to create various polymers

(nucleotides are ___________ of DNA)

Nucleotides

basic building blocks of DNA & RNA

Parts of Nucleotides

deoxyribose pentose sugar

phosphate group

nitrogenous base

Deoxyribose

sugar in DNA

Ribose

sugar in RNA that is has an additional oxygen as a hydroxyl group in #2 carbon

Phosphate Group

links two sugars together to build polymers

Phosphodiester

joins two sugars via phosphate vertically (joins two nucleotides)

Condensation Reaction

produces H2O when phosphodiester bonds from

Nitrogenous Base

four different nucleotides that make up a DNA polymer

Purine Deoxyribonucleotides

guanine & adenine (have 2 rings)

Pyrimidine Deoxyribonucleotides

thymine & cytosine (have 1 ring)

Uracil

takes the place of thymine in RNA

The Backbone

one strand of DNA made of repeating monomers covalently bonded together

Triplet Code

used to send instructions in the cell: to switch genes on and off to make proteins and enzymes

Hydrogen Bond

holds DNA strands together and is weaker than molecular bonds. Millions in a single molecule cause bases to attract each other.

Complementary Base Pairs

only bonds with each other (A&T or U) (C&G)

Antiparallel

one side up and the other down (in DNA the direction of the phosphate (5’end) on one strand and the hydroxyl (OH 3’end on the other)

DNA Replication

original copy of DNA is unzipped and replicated producing two new identical molecules of DNA

Purpose of DNA Replication

as a cell’s chromosomes are copied for cell division, DNA must be copied too, since DNA makes up chromosomes

instructions for making cell parts are encoded in the DNA so each new cell must get a complete set of the DNA molecules

Unwinding Double Helix

used in DNA replication, where each strand of DNA becomes a new template for a new strand. Each double stranded DNA contains the original copy and one new strand. Parent DNA molecule and two daughter molecules are identical (same nucleotides in same order) 

Helicase

enzyme (protein) that breaks the hydrogen bonds between nitrogenous bases to “unzip” or “unwind” the DNA helix. This is the first step in DNA replication

DNA Polymerase

enzyme that moves along the single strands of DNA and helps each free nucleotide bind to a new complementary base to form base pairs. This is the second step to DNA replication and happens as the DNA unzips. 

Semi-Conservative Model of Replication

one daughter strand is paired with a parent strand, one old one new is __________________

Why new cells are produced

for growth and to replace damaged or old cells, all cells are derived from pre-existing cells

Prokaryotes

organisms whose cells lack a nucleus and other organelles, for ex. bacteria

Eukaryotes

organisms whose cells contain membrane-bound organelles for ex. Animals 

Eukaryotic Chromosomes

store genetic information, have between 10-50 chromosomes in their body cells, human body cells have 46 chromosomes (23 pairs)

Chromatin

long uncoiled strand of DNA that takes up less space in a cell. They can’t be seen when cells aren’t dividing.

Histones

a protein which DNA is tightly coiled around to form structures call nucleosomes. Makes mixed up DNA strands into sticks/chromatin

Chromatid

duplicated chromosomes which aren’t held together by the centromere

Centromere

holds sister chromatids together

Asexual Reproduction

a single cell dividing to make 2, identical daughter cells

Sexual Reproduction

involves two cells (egg & sperm) joining to make a new cell (zygote) that is not identical to the original cells

5 Phases of Cell Cycle

Interphase (G1 - primary growth, phase)

(S synthesis; DNA replicated)

(G2 - secondary growth phase)

Mitosis

Cytokinesis

Interphase (G1)

1st growth stage after cell division, Cells mature by making more cytoplasm & organelles, so daughter cells have all organelles, Cell carries on its normal metabolic processes

Interphase (S stage/synthesis)

DNA is copied or replicated

Interphase (G2)

2nd growth stage, occurs after DNA has been copied, all cell structures needed for division are made (ex. Centrioles which move to poles), both organelles & proteins are synthesized

Mitosis/Karyokinesis

Division of the nucleus, only occurs in eukaryotes, has 4 stages, doesn’t occur in some specialized cells such as brain cells

Early Prophase

Chromatin in nucleus condenses to form visible chromosomes (creates absence of space in nucleus), Mitotic spindle forms from fibers in cytoskeleton or centrioles (animal)

Late Prophase

Nuclear membrane & nucleolus are broken down, chromosomes continue condensing & are clearly visible, spindle fibers called kinetochores attach to the centromere of each chromosome (Only called kinetochores only if they grab the centromere of the chromosome called the astor if it doesn't) Spindle finished forming between the poles of the cell 

Metaphase

Chromosomes, attached to the kinetochore fibers, move to the center of the cell, chromosomes are now lined up at the equator (or _________ plate), preparing for the actual division of the chromosomes

Anaphase

Occurs rapidly, high forced, sister chromatids are pulled apart to opposite poles of the cell by kinetochore fibers

Telophase

Sister chromatids at opposite poles, Spindle disassembles (disappears), Nuclear envelope (nuclear membrane) forms around each set of sister chromatids, Nucleolus reappears, Cytokinesis occurs, Chromosomes reappear as chromatin

Cytokinesis

division of the cytoplasm, Division of the cell into half, in plant cells, cell plate forms at equator to divide cell, In animal cells, cleavage furrow forms to split cell 

Daughter Cells of Mitosis

Have the same number of chromosomes as each other and as the parent cell from which they were formed, Identical to each other, but smaller than parent cell, Must grow in size to become mature cells (G1 of Interphase)

Checkpoints in the Cell Cycle

messages sent to the cells nucleus to “divide, or not to divide” at: G1, S Synthesis phase (DNA Replication): cyclins/cyclin dependent kinase signals the division, G2 gap phase 2- cell size/energy reserves are assessed and if all chromosomes have been replicated correctly, M checkpoint (metaphase): spindle checkpoint, are the sister chromatids attached correctly 

Meiosis

occurs after interphase to form gametes, starts with 46 double-stranded chromosomes which is 23 pairs of homologous chromosomes. Is called a reduction - division. The original cell is diploid (2n) 4 daughter cells are produced that are haploid (1n)

Meiosis I

homologous chromosomes separate, 23 double stranded chromosomes after division

Meiosis 2

sister chromatids separate (end up with 4 haploid cells), 23 single stranded chromosomes after division

Zygote

a fertilized egg cell - when two haploid (1n) gametes (sperm and egg cell) fuse to form a diploid (2n) zygote. 23 chromosomes from father, 23 from mother 

Early Prophase I

chromosomes number doubled, forms homolog pairs 

Late Prophase I

the chromosomes condense, crossing over occurs, spindle fibers form, and the nuclear envelope fragments

Metaphase I

homologous pairs of chromosomes align along the equator of the cell, so there are two rows of chromosomes. centromeres are at the opposite sides of the cells, and this is where the mitrotubules attach to the centromere/kinetochore

Anaphase I

homologs separate and move to opposite poles, sister chromatids remain attached at their centromeres. Each copy of chromosomes are on separate sides of the cell. They are not entirely identical, as it’s composed of different characteristics (from paternal or maternal one can have more than the other)

Telophase I

the nuclear envelopes reassemble, spindle disappears, and it now divides the cell into two, as the cells are now haploid

Cytokinesis I/Interkinesis

chromosomes completely uncoil to become chromatin, nuclear membrane completely reforms 

Meiosis II

only one homolog of each of the chromosome is present in the cell, and the sister chromatids carry identical genetic information

Interphase II

the cells prepare for division, chromatin begins to coil/condense into chromosomes, however the DNA is not duplicated so it remains a haploid (n)

Prophase II

the nuclear envelope fragments, chromosomes condense, the spindle forms, however there is no crossing over

Metaphase II

chromosomes line up at the center of the cell (no longer in pairs through), independent assortment occurs again of the sister chromatids, and the microtubules attach to the centromere/kinetochore

Anaphase II

the sister chromatids separate and now move to opposite poles of the cell, and continue to be haploid

Telophase II

the nuclear envelope assembles, chromosomes now uncoil, spindle disappears, and now cytokinesis occurs by dividing the cell into two. There is now 4 haploid daughter cells. 

Cytokinesis II

produces 4 haploid daughter cells

Results of Meiosis

the gametes (egg & sperm) form, as four of the haploid cells contain one copy of each chromosome. there is one allele for each gene, and it contains different combinations of alleles for different genes along the chromosome

Gametogenesis

gamete formation

Spermatogenesis

production of sperm

• meiosis takes place in testes

• begins with diploid cell called a spermatogonium

Oogenesis

production of eggs

• meiosis takes place in the ovaries

• begins with a diploid cell called an oogonium

• Oogonia reproduces by mitosis, then oocyte begin meiosis but stops at prophase 1 till meiosis 1 continues for the cell each month beginning at puberty. Creating an unequal division of cytoplasm (a polar body and a visible egg)

Gamete formation in animals

• Meiosis in mammals differs drastically between males & females

• two types of ____________ in humans

  • Spermatogenesis

  • Oogenesis

Spermatogonium (pl: Spermatogonia)

• a diploid that starts spermatogenesis

• _____________ reproduces by mitosis and resulting cells undergo meiosis

• 1 _____________ produces 4 sperm

Polar Body

created during oogenesis and will eventually degenerate

Oogonium (pl: Oogonia)

• a diploid cell that starts oogenesis

• _________ reproduces by mitosis, then begins meiosis but stops at prophase 1

Major differences between Spermatogenesis & Oogenesis

• cytokinesis is unequal among daughter cells during __________

• at birth, the ovaries contain all the cells it will ever have that will develop into eggs

  • sperm continue to develop by meiosis throughout the male reproductive years

• __________ has a long resting period after prophase 1 until hormones activate them

Why is cytokinesis is unequal during oogenesis

• ensures only one zygote is formed during fertilization

• more nutrients given to 1 egg to ensure survival or zygote

• more than one zygote means nutrients are divided (increases chance of health complications)

400,000 - 500,000 eggs

• all the cells in the ovaries that will ever develop into eggs

• only 400 will mature and become eggs

• each egg will complete division process upon puberty one at a time

Fraternal Twins

When more than 1 egg is released and both are fertilized (diff DNA)

Identical Twins

A single zygote divides into two separate bodies (genetically identical)

Importance of Meiosis

provides a vast amount of genetic variation

Independent Assortment

How pairs orient themselves in Metaphase1 and Metaphase2 will determine their variance (diff combos of chromosomes). In Anaphase1 homologs pairs independently separate, in Anaphase2 sister chromatids independently separate.

• 2ⁿ

2ⁿ

• number of genetically distinct gametes that can be produced from a diploid cell during independent assortment

• n = number of chromosome pairs

• In humans 2²³ = 8,388,608

Crossing Over

In prophase1 chromosomes exchange DNA by ________ each other

• occurs in several points along non-sister chromatids

• result: chromosomes have genes form maternal & paternal origin

• bonds holding DNA together are broken & reformed (might not reform correctly)

Errors Cause by Changes in Chromosome Structure

Deletion, Duplication, Inversion & Translocation

Deletion

• a piece of the chromosome deleted/lost

• missing gene = info form making vital proteins missing

• can be caused by: viruses, irradiation, chemicals