Chromosome Inheritance Notes Flashcards
Why does down syndrome happen?
abnormal number of chromosomes
chromosome abnormality in 21
How can an extra chromosome cause a wide range of
phenotypic effects?
- Chromosomes transmit genetic information
- The type and amount of genetic material is important for normal development
Chromosomes
are structures within living cells that contain the genetic material
What are chromosomes composed of?
- DNA (genetic material)
- Proteins (chromatin), provides organized structure
- Eukaryotic chromosomes: linear and contained in the nucleus
- Prokaryotic chromosomes: circular and located in the nucleiod
Chromosome structure in the nucleus
Chromosomes are present in the nucleus as chromatin
Chromatin
a long thread primarily made of DNA with some protein scaffolding
When does chromatin duplicate and condense?
In preparation for cell division (mitosis or meiosis)
it condenses and duplicated into visible chromosomes of a karotype
What are duplicated chromosomes called?
Chromatids
What are chromatids joined by?
Centromere
How many chromosomes do humans have?
46 (23 pairs)
- you get 23 from mom, 23 from dad
Dogs chromsomes
78 (39 pairs)
Cat chromsomes
38 (19 pairs)
Horse chromsomes
64 (32 pairs)
Cow chromsomes
60 (30 pairs)
Rice chromsomes
24 (12 pairs)
Corn chromsomes
20 (10 pairs)
Potatoes chromsomes
48 (24 pairs)
Centromere
- located at the center of a chromsome
- Holds sister chromatids together and is important
for cell division
Telomeres
- located at the end of chromosomes (caps)
- protective ends that prevent degradation.
Chromosome Arms
- Short arm (p)
- Long arm (q)
Sister chromatids
- both chromosomes replicated
- the two exact copies
How does the length of the arms and the centromere help in the function of the chromosome?
Helps in function, stability, and genetic disorders (plays a role)
Types of cells in plants and animals
Somatic and germ cells
Somatic cells
- make up a big majority of cells in an organism
- in G0 phase of going through mitosis
Germ cells
are precursors (before) to gametes
* Set aside during embryogenesis
* Become incorporated into reproductive organs
* Only cells that undergo meiosis to produce haploid gametes
Mitosis
Nuclear division that generates two daughter cells containing the same number and type of
chromosomes as parent cell
Meiosis
Nuclear division that generates gametes (egg
and sperm) containing half the number of chromosomes
found in other cells
Purpose of Mitosis
- growth and repair
Number of cells produced in mitosis
2 identical cells
Is there genetic variation in mitosis?
No
Purpose of Meiosis
Sperm, egg production
Number of Cells produced in Meiosis
4 unique cells
Is there genetic variation in meiosis?
Yes
What is the cell cycle?
a repeating pattern of cell growth and division
an alternation between interphase and mitosis
What does nuclear divison during mitosis create?
- two genetically identical daughter cells
How many parts does interphase have?
Three, Period of cell growth and chromosome duplication between divisions
Parts of interphase
- Gap 1(G1) Phase
- Synthesis (S) Phase
- Gap 2 (G2) Phase
Formation of microtubles in cytoplasm
Centrosome, centrioles
Centrosome
microtubule organizing center near the nuclear
envelope
Centrioles
core of centrosome (not found in plant cells
When does most cell growth occur in the cell cycle?
G1 and G2 Phase
Do some cells stop dividing in the cell cycle?
Yes, some cells stop dividing and arrest in the G0 phase
What phase does chromosomes replicate to form sister chromatids?
S phase
Checkpoints of the Cell Cycle
- each step has to be complete before moving onto the next
- helps prevent errors in cycle
What happens in the G1 phase?
cell growth, chromosomes are not
duplicating or dividing
interphase; Gap before duplicatio
What happens in S phase?
duplication of
chromosome into sister
chromatids
DNA synthesis and chromsome duplicaition
What happens in G2 Phase?
cell growth,
synthesis of proteins
required for mitosis
G2: interphase Gap before mitosis
Diploid
2n (each chromosome pair has one material and paternal copy)
Haploid
n (gametes, carry only a single set of chromosomes)
What fuses during fertilization to form a zygote
Two gametes
What are zygotes?
diploid (2n) carry two matching sets of chromosomes, one each from egg and sperm
What is Metacentric chromosome?
Centromere is in the middle
What is Acrocentric chromosome?
Centromere is near one end
Homologs
contain same set of genes but have different alleles
Non-homologous
carry unrelated set of genes
Karotype
Micrograph of stained chromosomes
arranged in homologous pairs
Autosomes
all chromosomes except x and y
Sex chromosomes
unpaired x and y
Nondisjunction
homologs of a chromosome pair segregate during meiosis 1
can result in abnormal chromosome (down (trisomy)
How does meiosis contribute to genetic diversity?
Independent assortment of nonhomlogs created differenet combinations of alleles across gametes
Crossing-over between
homologs creates different
combinations of alleles within
each chromosome
Cytokinesis
- final stage of cell divison
- Begins during anaphase but not completed until after
telophase - Cytoplasm of parent cells split into two daughter cells with
identical nuclei
Cytokinesis definition
- the cytoplasm divides and produces two
daughter cells
Cytokinesis in animals
- In animals – contractile
ring that contracts to
form cleavage furrow - organelles (for example, ribosomes,
mitochondria, Golgi
bodies) are distributed to each daughter cell
Cytokinesis in plants
- In plants – have cell
plate that forms near
equator of cell
*organelles (for example, ribosomes,
mitochondria, Golgi
bodies) are distributed to each daughter cell
