biology 3592 midterm

What is the chromosomal basis of human heredity?

DNA packaged into chromosomes transmitted during mitosis and meiosis.

What are nucleotides?

Building blocks of DNA, consisting of a base, sugar, and phosphate group.

What is the structure of DNA?

Double helix formed by two strands of DNA with proteins as the functional molecules.

What are the functions of proteins in DNA?

Produce polypeptides, RNAs, and specify cellular characteristics.

How is DNA packaged in somatic cells?

46 linear chromosomes, including 22 pairs of autosomes and 1 pair of sex chromosomes.

What is the mitochondrial chromosome?

Circular chromosome with its own genome and genes, maternally inherited.

What is the size and gene content of the mitochondrial chromosome?

About 16,600 bp with 37 genes involved in oxidative phosphorylation.

What is the origin of the mitochondrial chromosome?

Thought to originate from bacteria.

What is the role of mitochondria in energetically costly cells?

More energetically costly cells require more mitochondria.

Do mitochondria in sperm donate their DNA?

No, mitochondria in sperm do not donate their DNA.

How many chromosomes are present in somatic cells?

Two chromosomes, one from the mother and one from the father.

How is chromosome number determined?

Chromosome number is based on size

which chromosomes are not in order of size?

21 and 22, 21 is smaller

Does a larger chromosome always have more genes?

Generally, larger chromosomes have more genes, but gene distribution can vary.

What percentage of DNA codes for protein?

Only about 1.5% of DNA codes for protein.

What percentage of the human genome is composed of repetitive sequences?

About 50% of the human genome is composed of repetitive sequences.

What are the types of repetitive DNA in the human genome?

Tandem repeats (repeated one after another) and interspersed repeats (spread throughout the genome).

What is the role of complementarity in DNA replication?

Complementarity allows for precise replication of DNA.

How many protein coding genes are there in the human genome?

About 19-20,500 protein coding genes.

What is chromatin?

DNA and associated proteins

What is a nucleosome?

DNA wrapped around a histone protein

What is the histone octamer?

A complex of four different histone proteins (H2A, H2B, H3, H4)

What is the function of H1 in chromatin structure?

Causes the winding of DNA into the 30 nm structure

What is the structure of the 10 nm fiber?

Beads on a string

What is the structure of the 30 nm fiber?

Coiling into a solenoid

What is the somatic cell cycle?

Process of producing identical copies of somatic cells

What happens during interphase?

Majority of the cell cycle spent in this phase, DNA replication occurs in S phase

What is G0 phase?

Permanent arrest in G1 phase

What are the stages of mitosis?

Prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis

What happens during prophase?

Chromosome condensation and spindle formation

What happens during prometaphase?

Nuclear membrane breaks up and chromosomes start moving towards the middle

What happens during metaphase?

Maximal condensation and chromosomes align at the equatorial plane

What happens during anaphase?

Chromosomes separate at the centromere

What happens during telophase?

Chromosomes decondense and nuclear membrane reforms

What is cytokinesis?

Division of cytoplasm

How many chromosomes are present in all phases of the cell cycle?

46 chromosomes

What are sister chromatids?

Replicated chromosomes

What is chromosome spread?

Chromosomes from metaphase or prometaphase used for identification

what is the p arm of a chromosome?

short arm

what is the q arm of the chromosome?

long arm

What is cytogenetic chromosome banding?

Staining technique to identify chromosomal abnormalities

What is meiosis I?

Separation of homologous chromosomes

What is meiosis II?

Separation of sister chromatids

What happens during meiosis I?

Reduction division, reduction from 2n to n

when does recombination occur in meiosis?

prior to reduction

What happens during meiosis II?

Similar to mitosis, separation of sister chromatids

What is the result of meiosis I?

Haploid cells

What is recombination in meiosis?

Exchange between paternal and maternal chromosomes

What determines the composition of each transmitted chromosome?

Number and location of cross overs

What is the composition of transmitted chromosomes after recombination?

Both chromosomes are ~50% grandmaternal and ~50% grandpaternal

What happens during prophase I of meiosis?

Recombination takes place

What is the first stage of prophase I?

Leptotene

What happens during leptotene?

Chromosomes come together, DS breaks occur (potential sites of recombination)

What is the second stage of prophase I?

Zygotene

What happens during zygotene?

Early recombination nodules form (not all result in recombination)

What is the third stage of prophase I?

Pachytene

What happens during pachytene?

Recombination actually takes place, number of events relative to chromosome size, some regions are hotspots for recombination

What is the final stage of prophase I?

Diplotene/Diakinesis

What holds homologs together?

Chiasmata

How many chiasmata per chromosome?

1-2

How many chiasmata per sperm?

~50

Where does crossover happen?

Between Z and P

What are the similarities between Metaphase I and Anaphase I with mitosis?

Homologous chromosomes

What happens during Metaphase I?

Nuclear membrane disappears, spindle forms, alignment of chromosomes on the equatorial plane, crossover events have occurred, chiasmata formed

What happens during Anaphase I?

Homologous chromosomes move apart, reduction from 2n to n

What is the result of meiosis?

Haploid cells

What are the genetic consequences of meiosis?

Many disorders follow Mendelian patterns, reduction of chromosome number, segregation of alleles, independent assortment, crossing over

What is Mendel's first law?

Law of segregation, alleles for each gene segregate from each other during gamete formation

What is Mendel's second law?

Law of independent assortment, genes for different traits can segregate independently during gamete formation

What is the result of independent assortment of chromosomes?

Over 8 million combinations of chromosomes

What is gametogenesis?

Process of forming gametes

What is the difference between spermatogenesis and oogenesis?

Differences in detail and timing

When is female meiosis initiated?

Early during fetal life, from limited number of cells

When is male meiosis initiated?

Throughout adult life, from many dividing cells

What is spermatogenesis?

Formation of sperm in the testes.

What is the final stage of spermatogenesis?

Primary spermatocyte.

What happens during meiosis I in spermatogenesis?

Primary spermatocyte undergoes meiosis I.

What happens during meiosis II in spermatogenesis?

Secondary spermatocytes undergo meiosis II.

How long does spermatogenesis take?

Approximately 64 days.

What is oogenesis?

Formation of eggs in the ovaries.

When does oogenesis begin?

During prenatal development.

Where do ova develop from?

Oogonia cells in the ovarian cortex.

What happens during the 3rd month of oogenesis?

Primary oocytes begin to develop.

What happens to most of the primary oocytes?

Many degenerate.

How many primary oocytes remain arrested in prophase I until sexual maturity?

Approximately 400.

What happens during prophase I of oogenesis?

Crossover occurs.

How many oocytes are ovulated per month?

Approximately 1.

What happens to the oocyte prior to ovulation?

It rapidly completes meiosis I.

What is the result of meiosis I in oogenesis?

Formation of a secondary oocyte and a first polar body.

What happens during fertilization?

The gDNA from the sperm remains in the egg.

What happens to the mitochondrial material in the sperm following fertilization?

It is broken down and not utilized.

What happens to the pronuclei during fertilization?

They fuse.

How does the zygote divide after fertilization?

By mitosis, producing diploid daughter cells.

What is trisomy 18 karyotype?

An abnormal karyotype resulting from non-disjunction.

What can cause non-disjunction?

Failure of chromosomes to segregate properly in meiosis.

Are non-disjunction events more prevalent in male or female meiosis?

They may be more prevalent in both.

What is the relationship between Down syndrome and maternal age?

Down syndrome is highly related to maternal age.

Can non-disjunction occur in the production of sperm?

Yes, it can also be more prevalent in sperm production.

What is the central dogma?

DNA is transcribed into RNA, which is translated into protein.

How many protein coding human genes are there?

Approximately 20,000.