Chapter 13 Flashcards
Transmission of traits fromone generatin to the next is called
Heredity
Scientific study of heredity and hereditary variation
Genetics
Discrete units of hereditary information consisting of a specificc nucleotide sequences in DNA
Genes
What are gametes?
Reproductive cells- sperm and egg
DNA is packaged into
Chromosomes
Each chromosome consists of??
A single long DNA molecule coiled in association with various proteins
A gene’s specific location along the lenght of a chromosome
Locus
Asexual reproduction
Genestically identical offspring- produced by mitosis
Sexual reproducation
Unique combinations of gene’s inherited from 2 parents
The generation to generation sequence of stages in the reproductive history of an organism from conception to production of its own offspring is called
Life cycle
Display of condensed chromosomes arranged in pairs is called
Karyotype
A pair of chromosomes have:
- Same lenght
- Same centromere position
- Same staining pattern
- Are called homologous chromosomes or homologs
Sex chromosomes
Female: XX
Male: XY
Nonsex chromosomes are called
Autosomes
The “n” number is the number of chromosomes in a
Single set-haploid
Cell with 2 chromosomes sets referred to as 2n
Diploid cell
Diploid number In humans is
46-thus 2n=46
Haploid number in humans is
23 (23 autosomes & single sex chromosomes)
Union of gametes
Fertilization
What is a zygote?
Fertilized egg and is 2n
The only cells not produced by mitosis is
Gametes
Mitosis results in
2 daughter cells
Meiosis results in
4 non identical daughter cells
Sister chromatids make up one replicated
chromosome
The two chromosomes of a homologous pair are individual chromosomes that were inherited from
different parents
3 events unique to meiosis that occur during meiosis 1
- Synapsis and Crossing Over
- Homologs on the metaphase plate
- Seperation of homologs
Meiosis is often called reduction division because it halfes the number of?
Chromosomes
Origins fo genetic variaton among offspring
- Independent assortment of chromosomes
- Crossing Over
- Random fertilization
Not associated with asexual reproduction
Meiosis
A cell having 22 autosomes and an “x” chromosomes would be?
egg or sperm
A cell that has 24 chromosomes in each somatic cell that is made of 12 homologous pairs has a diploid number of? and haploid of?
Dipoild-24
Haploid-12
Fertilization produces a zygote which is
Diploid
When does crossing over occur?
Prophase 1
A cell with 20 chromosomes has how many chromosomes in each daughter cell after mitosis
20 chromosomes
A cell with 20 chromosomes has how many chromosomes in each daughter cell after meiosis
10 chromosomes
Gametes are always
Haploid
After which process does a diploid cell change to haploid?
Meosis 1
Meiosis 1
- Homologous chromosomes seperate
- Results in 2 haploid daughter cells which replicated chromosomes
- Halves the # of chromosomes
Phases of meiosis 1
- Prophase 1
- Metaphase 1
- Anaphase 1
- Telophase 1 and cytokinesis
Prophase 1
- Occupies 90% of time reequired for meiosis
- Chromosomes begin to condense
- Synapsis-homologous chromosomes loosely pair up, aligned gene by gene
- Crossing-Over occurs in sister chromatods & exchange of DNA segments
- Each pair of chromosomes forms a tetrad (a group of 4 chromastids)
- Each tetrad usually had one or more chiasmata (X-shaped regions where crossing overoccured)
Metaphase 1
-Tetrads line up at the metaphase plate
Anaphase 1
- Pairs of homologous chromosomes seperate
- One chromosome moves toward each pole, guided by the spindle fibers
Telophase 1
- Each half of the cell has a haploid set of chromosomes
- Each chromosome still consists of 2 sister chromatids
Cytokinesis in Meiosis
Occurs simulataneously
- Forming 2 haploid daughter cells
- in animal cells- a cleavage furrow forms
- In pplany cells- a cell plate forms
Meiosis 2
- Sister chromatids seperate
- Results in 4 haploid daughter cells with unreplicated chromosomes
- Very similar to Mitosis
Phases of Meiosis 2
- Prophase 2
- Metaphase 2
- Anaphase 2
- Telophase 2 and cytokensis
Prophase 2
- A single apparatus forms
- Chromosomes (2 chromatids) move toward the metaphase plate
Metaphase 2
- Sister chromatids are arranged at the metaphase plate
- Kinetochores of sister chromatids attach to microtubles extending from opposite poles
Anaphase 2
- Sister chromatids seperate
- Sister chromatids of each chromosome now move as 2 newly individual chromosomes toward opposite poles
Telophase 2 and Cytokinesis
- Chromosomes arrive at opposite poles
- Nucei form and the chromosomes being decondensing
- Cytokinesis seperates the cytoplasm
Result of Meiosis
- 4 daughter cells (each with a haploid set of unreplicated chromosomes)
- Each daughter cell is genetically distinct from the others and from the parent cell
3 mechanisms contribute to genetic variation
- Independent assortment of chromosomes
- Crossing over
- Random Fertilization- because any sperm can fuse with any ovum
Number of daughter cells in mitosis
Same as parent
Number of daughter cells in meiosis
Half as many
Mitosis results in
2 identical daughter cells
Meiosis results in
4 non identical daughter cells
Sister Chromatids
- Contains identical DNA molecule
- Attached by adhesive protein complexea called Cohesions
Centromeres
- narrow waist of the duplicated chromosome
- Region where the 2 chromatods are most closely attached
Gametes
- Reproductions cells (sperm and egg)
- Half as many chromosomes as somatics cells
Chromatin
A complex of DNA and proteins
Prophase
- Chromatin fibers beccome more tightly coiled (chromosomes)
- Nucleloi diappear
- Each duplicated chromosome appears as 2 identical sister chromatids joined at their centrometers
- Mitotic spindle begins to form
Mitotic spindle
apparatus of microtubles that controls chromosomes movement during mitosis
Chromosomes and microtubules attach to one another at
Kinetochore
