Genetics chapter 1 and 2

gene

a ‘unit’ of heredit

• is a segment of DNA that produces a functional product such as a polypeptide

Genes provide

the blueprint that determines the traits of an organism

Traits

are the observable characteristics of an organismMost

Most human cells contain

• 46 human chromosomes, 23 pairs

• 22,000 coding genes

  • 3 billion dna base pairs per set of chromosomes ( containing A,T,G, and C)

Diploid

refers to a cell or organism that contains two sets of chromosomes (i.e. somatic cells)

• denoted as "2n" and represents the total number of chromosomes present in most cells

Haploid

refers to a cell or organism that contains a single set of chromosomes. In humans, this refers to cells such as gametes (sperm and egg cells)

• carry half the genetic information necessary for a new individual.  (n)

Somatic cells

Body cells, other than gametes

• Blood cells, for example

Germ cells

Gametes

• Sperm and egg cells

Cytogenetics

The field of genetics that involves the microscopic examination of chromosomes

•Centromeres

Constricted regions on chromosomes

• Location of centromere establishes appearance of chromosome

Centromere: Long arm =

q arm

Centromere: short arm =

p arm

Centromere: Metacentric

middle

Submetacentric

between the middle and end

Acrocentric

close to end

At end

at end

cell division purpose

asexual reproduction

achieving multicellularity

G0 phase

A cell may remain for here long periods

• in this phase is all cell decides to ither progress through the cell cycle or divide again

• Terminally differentiated cells (for example adult nerve cells)

G1 phase

Cell commits and prepares to divide

period where cell increases its supply of proteins and number of organelles

• DNA is checked for errors

S phase - interphase - DNA replication

Cell chromosomes are replicated → chromatids (2 copies) → form sister chromatids

• cell now has twice as many chromosomes as the G1 phase (46 chromosomes in G1 → 46 sister chromatids in S phase)

G2 phase - protein synthesis

cell grows and increases the number of proteins necessary for cell division

M phase - miotic phase - cell diviosion

Cell is subdivided through prophase, metaphase, anaphase, telophase, and cytokinesis resulting in to identical daughter cells

Mitosis: 46 pairs of sister chromatids are separated and sorted Thus, each daughter cell receives

46 chromosomes

In a cell preparing for mitosis, you see two identical copies of a chromosome held together by a centromere. HC or SC?

sister chromatids

A person inherits a chromosome carrying the gene for blue eyes from their mother and a chromosome carrying the gene for brown eyes from their father. HC or SC?

Homologous chromosomes

A cell contains four chromosomes in total, with two pairs that look similar but may have different alleles of  genes for specific traits. HC or SC?

Homologus chromosomes

There are 100% identical and generated during S-phase. HC or SC?

sister chromatids

Consider an original mother cell that is diploid (2n).

It contains a total of?

4 chromosomes

• Two chromosomes per set (n= 2)

Interphase

Chromosomes decondense forming chromatids (6 pairs not seen until prophase)

• centrosome, the attachment point of the mitotic spindle, divides

Spindle Apparatus- Needed for M phase

Microtubules

• are formed by rapid polymerization of tubulin proteins

There are three types of spindle microtubules

• Aster microtubules

• Polar microtubules

• Kinetochore microtubules

Aster microtubules

Important for positioning of the spindle apparatus

Polar microtubules

Help to “push” the poles away from each other

Kinetochore microtubules

Attach to the kinetochore, which is bound to the centromere of each individual chromosome

Prophase

Chromatids coil up and condense

centrioles divide and move apart

Prometaphase

centrioles reach the opposite poles, spindle fiber from

Kinetochore microtubules grow

Prometaphase: Kinetochore microtubules grow from the two poles

• If they make contact with a kinetochore, the sister chromatid is “captured”

• If not, the microtubule depolymerizes and retracts to the centrosome

Prometaphase two kinetochores on a pair of sister chromatids are attached to

kinetochore MT on opposite poles

Metaphase

Pairs of sister chromatids align themselves the metaphase plate

• Each pair of chromatids (dyad) is attached to both poles by kinetochore microtubules

Cohesin

protein complex that holds sister chromatids together

Separase

Enzyme that degrades cohesin

Shugoshin

Protein that protects cohesin from being degraded by separase

Anaphase

centromeres split and daughter chromosomes migrate to opposite poles

As anaphase proceeds

Kinetochore MTs-

shorten

• Chromosomes move to opposite poles

As anaphase proceeds

Polar MTs lengthen

Poles themselves move further away from each other

elongating the cell

Telophase

Daughter chromosomes arrive at thr poles

cytokensis commences

• nucleus membrane froms two separate nuclie

Outcome of Mitotic Cell Division

produces two daughter cells are genetically identical to each other

• ensures genetic consistency from one cell to the next

development of multicellularity relies on

the repeated process of mitosis and cytokinesis

Meiosis

Parents (diploid) make gametes with half the amount of genetic material (haploid)

• These gametes fuse with each other during fertilization to create a new diploid individual

Gametes

1n

contains only 23 chromosomes

Unlike mitosis, meiosis involves

two successive divisions to reduce the chromosome content (termed meiosis 1 and 2). Each meiotic division is subdivided into:

• Prophase

• Prometaphase

• Metaphase

• Anaphase

• Telophase

Meiosis: Prophase 1 is further subdivided into five stages known as

• Leptonema

• Zygonema

• Pachynema

• Diplonema

• Diakinesis

meiosis beging with _____ and ends with _____.

one cell with 4 diploid chromosomes (2n = 4)

4 genetically differentiated haploid cells, each with two chromosomes (n = 2)

Meiosis significantly increases the

level of genetic variation due to crossing over

Mitosis vs meiosis II

For a diploid organism with six chromosomes

• Mitosis begins with 12 chromatids joined as six pairs of sister chromatids

• Meiosis 2 begins with 6 chromatids joined as three pairs of sister chromatids

Sexual Reproduction

Parents (diploid) make gametes through the process of gametogenesis with half the amount of genetic material (haploid)