Unit 7 - Genetics Flashcards
Purpose of Meiosis
A special type of cell division to make of gametes (sex cells - egg or sperm)
(how a diploid cell becomes a haploid cell)
Steps of Meiosis 1
Interphase - G1 - cell grows
S - DNA is replicated
G2 - preps itself for division
Prophase I
- Homologous pairs (replicated chromosomes paired with corresponding homologous chromosome) come together to form a tetrad. Crossing over occurs.
- nuclear envelope disappears
Metaphase I
- Tetrads (homologous pairs) meet in the middle & connect to spindle fibers (side by side)
Anaphase I - Spindle fibers pull apart the homologous pairs.
Telophase I - nuclear mem. forms around each “cluster” of separated chromosomes
Cytokinesis - It is split and 2 new cells are then formed
Steps of Meiosis 2
Prophase II - homologous pairs of chromosomes become visible
Metaphase II - Chromosomes line up in the center of each cell (vertically)
Anaphase II - The paired chromatids separate
Telophase - nuclear mem. forms around each “cluster” of separated chromosomes
Cytokinesis - the two original cells produced in meiosis I are finally divided into 4 haploid daughter cells
How Crossing Over Leads to Genetic Diversity
When the homologous pairs exchange part of their DNA during Prophase I, which creates NEW chromosomes!
Amt. of Chromosomes in Body Cells VS. Gametes (+ what are Gametes?)
Human body cells have 46 chromosomes - are diploid
Gametes (human eg or sperm cells) have 23 chromosomes - are haploid
Gametes are sex cells (sperm and egg in human).
Compare + Contrast Meiosis + Mitosis
BOTH: begin with 1 diploid parent cell
Mitosis:
Purpose: To produce identical cells; to increase the number of cells; to replace cells.
Result: 2 genetically identical daughter cells.
Chromosome number: Remains the same (diploid to diploid).
Occurs in: body cells.
Genetic variation: No
Meiosis:
Purpose: To produce gametes (sperm/eggs) for sexual reproduction.
Result: 4 genetically unique daughter cells.
Chromosome number: Halved (diploid to haploid).
Occurs in: gametes - reproductive cells.
Genetic variation: Yes
Meiosis includes two rounds of division, Mitosis only includes one.
True Breeding
Producing offspring identical to themselves
EX: The result of the pea plant offspring (via self pollitnation) before Mendel decided to cross it.
Dominant + Recessive (complete dominance pattern)
Dominant - the trait of this gene will be expressed if there is 1 of the gene.
→ Shown by a capital letter (A)
Recessive - the trait of this gene will be expressed only if there are 2 versions of the gene (i.e. no dominant allele is present).
→ Shown by a lowercase letter (a)
Law of Segregation
the pair of alleles segregate from each other during meiosis so that each gamete will get one alelle.
Law of Independent Assortment
The alleles of multiple genes get sorted into gametes independently of one another (FOIL).
Autosome
All chromosomes other the sex chromosomes (remaining 44 chromosomes)
Incomplete Dominance
A BLEND of both traits occurs if heterozygous.
Co-Dominance
BOTH traits are shown if heterozygous.
Complete Dominance
Dominant OR Recessive determines traits.
Gene
Sections of DNA passed from one parental generation to the next.
Allele
Different versions of genes.
Trait
A specific characteristic of an individual.
Multiple Alleles
Having more than 2 alleles per trait (ex: ABO blood group)
Polygenic Traits
Multiple GENES control a trait (ex: skin type).
Sex - Linked Traits
Run through a form of inheritance where genes are located on a sex chromosome.
Pedigree
Chart used to analyze a pattern of inheritance of a trait within a family
Diploid + Haploid
Diploid - a cell having 2 of each chromosome
i.e. 46 chromosomes in a human body cell
Haploid - a cell having half or 1 of each chromosome
I.e. 23 chromosomes in gametes
