Chapter 2: The Human Genome and the Chromosomal Basis of Heredity Flashcards
hereditary material containing the genetic information
DNA
- units of genetic information
- they are organized along the chromosomes with with precise location or locus
genes
rod-shaped structures
chromsomes
maps the chromosomal location of the genes
gene map
species specific characteristic chromosome complement (number and morphology)
karyotype
-study of chromosomal structure and inheritance
cytogenetics
-normal human chromosome number is 46
nuclear genome
-refers to all cells in the body except those of the
gamete-forming germline - most are diploid
Somatic Cells
-members of a pair of chromosomes ->
carry same subset of genes arranged linearly along its DNA
Homologous chromosomes
-one of the alternate versions of a gene or DNA sequence
at a given locus
alleles
-located in the cytoplasm, have a small chromosome
which is an important part of the human genome
Mitochondria
What is the length of the mitochondrial chromosome?
16kb, which is about 16,000 nucleotides
- basic structural unit of chromatin
- appear as “beads on a string”
nucleosome
- a secondary heliical chromatin structure of coiled nucleosomes appear as a thick 30-nm diameter cylindrical fiber
soleonoid
What are the components that make up the DNA structure?
5-carbon deoxyribosenitrogen-containing purine (or pyrimidine base) phosphate group
How is a nucleotide formed?
when a deoxyribose and a phosphate group join
How may DNA molecules does the nuclear genome have?
46 DNA molecules
Which histones can be post-translationally modified?
H3, H4
What percentage do satellite DNA make up of all genetic material?
10-15%
How do you find satellite DNA?
arrays of various short repeats organized tandemly head to tail
different types of tandem repeats that can be separated as a distinct fraction of DNA
satellite DNA
long arrays of satellite DNA found in genetically inert regions on chromosomes 1, 9, and 16 and more than one-half of the Y chromosome
pentanucleotide repeats
What are 3 examples of dispersed repetitive DNA?
- Alu family
- LINE
- segmental duplications
What is special about the Alu family?
it is the best studied dispersed repetitive element
What is LINE?
a long interspersed nuclear element family composing ~20% of the genome. They are retrostransposons (copies can be integrated and cause insertional inactivation)
What is segmental duplication?
genetic rearrangements that can lead to gene deletions resulting in disease
Where does mitosis occur?
ordinary somatic cell division
What does mitosis result in?
2 diploid daughter cells with 2n chromosomes identical to parent DNA
Where does meiosis occur?
in germline cells
What does meiosis result in?
in reproductive cell gametes that are haploid/contain 23 chromosomes
What is interphase?
period of biosynthesis and growth between two mitosis; has 3 checkpoints
What are the checkpoints of the cell cycle?
G1, G2, S phases
When does G1 occur? is there synthesis of DNA?
after mitosis; no synthesis of DNA
What happens in S phase?
chromosomes replicate to become bipartite with 2 sister chromatids
What are telomeres?
in the end of each chromatid, they ensure chromosome integrity during cell division
What is telomerase?
enzyme that maintains chromosome ends
What does it mean that DNA replication is a semiconservative process?
it means that one strand of the double helix is directly from the parent and the other is synthesized from that
What does the centromere do?
it holds the two sister chromatids together
during what phase do chromosomes start to condense?
mitotic phase (M phase)
What happens in M phase?
chromosomes condense and 1 chromatid of each chromosome is distributed to each daughter cell
What are the 5 stages of Mitosis?
Prophase, Prometaphase, Metaphase, Anaphase, Telophase
What happens in prophase?
chromosomal condensation and formation of mitotic spindle
What happens in prometaphase?
nuclear membrane breaks up, chromosomes attach to microtubule in kinetochore
What happens in metaphase?
maximum condensation and alignment at equatorial plane
What happens in anaphase?
chromsomes separate at centromere, sister chromatids separate and are independent daughter chromosomes, they move to opposing poles
What happens in telophase?
chromosomes begin to decondense, nuclear membrane begins to form
What is euchromatin?
It is the C-G rich portion of chromatin; it is genetically active
What is heterochromatin?
chromosomal segment that remains in interphase is mostly repetitive DNA with no genetic activity
What are the phases of Prometaphase in Meiosis 1?
Leptotene, Zygotene, Pachytene, Diplotene, Diakenesis
What are the consequences of Meiosis?
1) reduction of chromosome number from diploid to haploid
2) shuffling of genetic material due to random assortment of the homologues
3) additional shuffling of genetic material due to crossing over
What is G-banding?
technique used to stain chromosomes; it shows the base composition and distribution of repetitive DNA elements
What do you see in G-banding?
black and white alternating pattern
What happens in Leptotene?
you have separated homologues, sister chromatids are very close to each other and start to condense
What happens in zygotene?
sister chromatids begin to form a complex by synapsing; they line up by their entire length
what happens in pachytene?
the sister chromatids are now a tetrad and undergo crossing over
What happens in diplotene?
the bivalent are together, you have a chiasma which is where crossing over occured
What happens in diakenesis?
the bivalents separate
when does spermatogenesis start occuring
at puberty
Where are sperm formed?
in seminiferous tubules of testes
What forms spermatogonia?
primordial germ cells
In the developmental stage, what is the final cell type?
primary spermatocyte
What happens with the primary spermatocyte?
It undergoes meiosis 1, forming 2 halpod secondary spermatocytes
What cell type of spermatogenesis undergoes meiosis 2?
secondary spermatocyte to form four spermatids that later form sperm
When does oogensis occur?
at prenatal development
Into what does oogonia develop and does the resulting cell undergo meiosis 1 or 2?
oogonia develop into primary oocyte and then undergo meiosis 1
What happens with the primary oocytes that do not degenerate?
they remain in prophase 1 until menstruation
What happens before ovulation?
oocyte compeltes meiosis 1 becoming a secondary oocyte and first polar body
When does meiosis 2 proceed in oocyte?
after fertilzation to produce a fertilized mature ovum and second polar body
How long is S phase?
6-8 hours
How long is G1, S, G2 phase?
16-24 hours
How long is mitosis?
1-2 hours
Where are the most g bands? the least?
prophase; metaphase
formation of the mitotic spindle
prophase
nuclear membrane breaks up
prometaphsae
maximal condensation
metaphse
