unit 3 test review - genetics

Introduction to Cell Division:

List the 4 basic functions of cell division.

• Repair, replace, reproduce, and grow cells

Why can cells not grow in size indefinitely?

• Cells are limited in size because of limitations in their surface area to volume ratio, nutrient intake, and internal transport

• As cells grow larger, the essential materials travel within the cell less effectively 

Why is accurate cell division required for biological continuity?

• Accurate cell division ensures:

  • New cells receive the correct number of chromosomes

  • Preserving genetic information across generations.

What is chromatin?

• Fibres of SNA in its uncondensed form

How are chromatin and chromosomes related to one another?

• Chromatins condense to form chromosomes during cell division

• Chromosomes are made of tightly coiled chromatin

What is the importance of chromatin replication to successful cell division?

• Ensures new cell receives a complete set of DNA

List and describe the stages of chromatin replication.

• Initiation: Enzymes unwind the DNA at specific origins.
  
  

• Elongation: New strands of DNA are synthesized using each original strand as a template.
  
  

• Termination: DNA replication stops and the strands are checked for errors.
  
  

Mitosis:

What is mitotic cell division?

• Occurs in all cells except gametes

• 1 cell division

• 2 final daughter cells produced

• Same number of chromosomes in daughter cell compared to parent cell (diploid 2n = (n = 23))

• No tetrads (synapsis chromosomes)

• No crossing over

• Identical genetics to parent cell

• Repair, growth, reproduction

How much of a cell's life is spent in interphase and mitosis:

• Interphase: 95% of the cell’s life

• Mitosis: 5% of their cell-cycle time (less than 1 hour)

How can each of the following stages of mitosis be recognized?

• Interphase

  • Cell prepares to divide: growth, DNA replication, cell functions

• Early prophase

  • Chromatin begins to condense into visible chromosomes, nucleus present

• Late prophase

  • Nuclear membrane breaks down; spindle fibers being to attach to chromosomes

• Metaphase

  • Chromosomes line up in the middle (equator) of the cell

• Anaphase

  • Sister chromatids are pulled apart to opposite sides of the cell

• Telophase 

  • Two new nuclei start to form; chromosomes begin to uncoil; spindle fibers disappear.

• Cytokinesis:

  • Two new daughter cells are produced

What are chromatids and centromeres?

• Chromatids: 

  • Fibres of SNA in its uncondensed form

  • Exists during S phase of interphase to allow DNA to replicate

• Centromeres:

  • The region where sister chromatids are joined and where spindle fibers attach during mitosis.

Describe cytokinesis in a plant cell

• A cell plate forms in the center of the cell

• Develops into a new cell wall, dividing the cell into two

How does this differ from animal cell cytokinesis?

• The cell membrane pinches inwards to divide the cell into two

• Called the cleavage furrow

State another difference between plant and animal cell mitosis.

• No cell wall and cell plate in animal cells

• Animal cells have cleavage furrow in telophase rather than a cell plate

Meiosis:

What is meiotic cell division?

• Occurs in gamete cells

• Double (2) the cell division (PMAT occurs twice)

  • IPMAT I and PMAT II

• 4 final daughter cells produces

• Half amount of chromosomes as parent cell (haploid n)

• Tetrads form (synapsis chromosomes)

• Crossing over in prophase I

• Genetically different from parent cell

• Genetic diversity (genetic variation)

What is meant by the terms haploid (n) and diploid (2n):

• Haploid

  • Contains half the number of chromosomes (n) as the parent cell (2n)

  • Ex. sperm and egg cells in humans, meiosis

• Diploid

  • Containing pairs of chromosomes

    • All somatic cells are diploid

    • In humans 2n = 46

    • Zygote has 2n (n from female + n from male gametes) 

What are homologous chromosomes?

• Pair of chromosomes with the same genes at same location

• NOT identical

  • May carry different versions of the gene/trait (alleles)

• Same: Length, centromere location, banding pattern when stained 

How does cytokinesis of meiotic cell division differ in males and females in humans?

• Males = four equal sperm cells

• Female = unequal, haploid one large egg cell (ovum) and 3 smaller polar bodies cells (which degenerate)

Errors in Meiosis

• Two types of errors: Structure and Number

• Structure

  • Deletion: a piece of chromosome is deleted

  • Duplication: Chromosome section appears twice or more times

  • Inversion: Section of chromosome is inverted

  • Translocation: segment of chromosome is attached to a different non-homologous chromosome (it should pair with homologous (same chromosome))

• Number 

  • Nondisjunction: when homologous chromosome pairs or sister chromatids do nope separate during meiosis

Mendelian Genetics:

Why are pea plants an ideal organism for studying inheritance? (give 2 reasons)

• Easy and observable traits (ex. color and seed shape)

• Reproduce quickly (cross pollination or self pollination)

State Mendel's Principle of Dominance.

• When two different alleles are present, the dominant will show/mask to effect the recessive trait

State Mendel's Principle of Segregation.

• Alleles of genes separate during meiosis and each offspring receives one allele from each parent.

What is meant by the term incomplete dominance?

• No allele is completely dominant

• Blending phenotype

• New combination created

What is meant by the term codominance?

• Both traits/alleles are shown/expressed

• Heterozygous organism

  • Ex. black cow x white cow = cow with black and white spots

What is the purpose of a test cross?

• Determines genotypes of an organism showing a dominant trait

• Shows homozygous dominant or heterozygous

What disadvantage can you foresee in performing test crosses?

• Time consuming

• Many offspring to get clear results

• Many results to consider 

Distinguish between autosomes and sex chromosomes. How many pairs of each type do humans have?

• 46 total chromosomes in humans

• Autosomes: non sex chromosomes, control most traits, 22 pairs (44 chromosomes)

• Sex chromosomes: determine sex (XX female or XY male), 1 pair (2 chromosomes)

Sex-linked traits examples

• Color Blindness 

• Hemophilia (body’s ability to make blood clots)

What is a pedigree? How can a pedigree help to trace genetically inherited traits?

• A diagram of individual’s ancestors

• Used in human genetics to analyze Mendelian inheritance of a certain trait

• Used to track the inheritance of a gene

About Blood / Blood Types

• Types: A, B, AB, O

  • IAIA / IAi, IBIB / IBi, IAIB, ii

• Antigens

  • Substances (usually proteins)

  • Tiny markers on the surface of cells

  • Help determine blood type

  • Immune system uses antigens to recognize which cells belong in the body and which doesn’t

• Antibodies

  • Tiny proteins made by the body to fight off foreign antigens (blood types)

  • Look and attack cells that don’t belong

    • Such as wrong blood types

• Rh blood group (+) or (-)

  • Another kind of antigen on red blood cells

  • Have it = Rh (+)

  • Don’t have it = Rh (-)

• Agglutination

  • When blood cells clump together

    • Blocks blood flow and is dangerous

• Hemolysis

  • When red blood cells break open and release its contents

  • Happens due to bad reactions such as blood clotting

  • Can lead to serious damage like kidney damage

Definitions

• Genetics

• The study of heredity and variation of living organisms

• How genetic information is passed from one generation to the next

• Allele

• A trait/gene inherited from generations / parents

• Dominant allele

• Form of a trait that always appears when an individual has alleles for it

• Expressed in capital letters

• Recessive allele

• Form of a trait that always appears when an individual has 2 alleles for it (ex. aa)

• Phenotype

• Physical appearance/traits of an organism

  • ex . GOP: red x white

• Genotype

• Combination of alleles for any given trait / genetic makeup

  • Ex. GOP: XBXb x XbY

• Gene

• A designated segment of DNA on a chromosome

• Position of a gene on a chromosome is called locus / loci

• Genome

• The complete DNA sequence of an organism

• DNA

• The chemical name for the molecule

• Carries genetic instructions in all living things

• Packaging of DNA with histone proteins for storage to result in a condensed chromosome

• Structure: Have 3 components of nucleotides: Phosphate group, Pentose group, Nitrogenous bases

  • A, G, C, T/U,

  • Adenine (A), Guanine (G), Cytosine (C), Thymine (T) (DNA), Uracil (U) (RNA)

    • Base Pairing: A pairs with T/U (2 hydrogen bonds)

    • Base Pairing: G pairs with C (3 hydrogen bonds)

• Somatic cell

• A plant or animal cell that forms the body of the organism (not reproductive cells)

• Karyotype

• A photograph of sorted and paired homologous chromosomes in a cell

• Can show missing or additional chromosomes in a person

  • Helps determine chromosome errors and disabilities 

• Zygote 

• Result of a cell from two gametes fusing

• Synapsis 

• The alignment of homologous chromosomes 

• During prophase I and meiosis I

  • AKA crossing over (segments of DNA exchange with each other)

• Chiasma

• Point of contact or physical link between two non-sister chromatids

• Trisomy

• Gain an extra chromosome

  • Ex. down syndrome

• Monosomy

• Loss of one chromosome (nondisjunction)

  • Most are lethal (dangerous/deadly)

  • Can cause miscarriage 

• Genetic Reduction (outcome of meiosis)

  • Produces haploid daughter cells

• Genetic Recombination (outcome of meiosis)

  •  Different combinations of alleles

  • Genetic variation