Meiosis Flashcards
What are genes?
Discrete units of heredity that are made of DNA segments. They consist of specific nucleotide sequences.
How are genes passed to future generations?
Genes are passed to offspring via gametes (sperm and eggs)
Each gene has a specific chromosomal location known as a locus
Most DNA is packaged into chromosomes
What are somatic cells and how many chromosomes do they have?
Somatic cells are all the cells in multicellular organism except the sperm and egg cells.
They have 23 pairs of chromosomes and each pair are homologous (same length, centromere position, and staining pattern at corresponding loci. One is inherited from the mother and the other from the father)
Define Karyotype
An ordered display of the chromosome pairs of a cell arranged by size at different type
They can be used to screen for defective or abnormal chromosome numbers
What are sex chromosomes?
Chromosomes that determine an individuals sex. Can be XX (female/homologous) or XY (male)
What are autosomes?
The remaining 22 pairs of chromosomes that are not responsible for sex
What are homologous chromosome pairs?
Pairs of chromosomes that include one chromosome from each parent
What is a diploid cell?
Two chromosome sets (2n); one from the mother and one from the father
For humans, the diploid number is 46. (2n=46)
Describe chromosomes
Thread-like structures within nucleus, and consist of protein and a DNA molecule
After DNA synthesis has occurred,each chromosome is replicated
Each replicated chromosome consists of two identical sister chromatids
Define haploid
A single set of chromosomes (not a pair). Humans have 23 (n=23)
In a set 9f chromosomes, how many are autosomal and how many are sex Chromosomes?
Each chromosome set of 23 consists of 22 auto autosomes and a single sex chromosome
In gametes, what cell donates the X chromosome and which decides the sex?
The egg donates the X chromosome and the Sperm will donate either an C or Y chromosome.
What is fertilization?
Union of sperm and egg
What is a zygote and where does it get its chromosomes from?
A zygote is a fertilized egg and it has one set of chromosomes from each parent forming a pair with 46 chromosomes in total
What is a reduction division in regards to chromosomes?
It is when chromosome number changes from 46 to 23 or from diploid to haploid
Why do gametes undergo two phases of meiosis?
Because they need to undergo two cell divisions that result in four haploid daughter cells, with e@ch daughter cell containing half as many chromosomes as the parent cell.
What are the two divisions of meiosis?
Meiosis 1(reductional division): where homologous chromosomes separate
Meiosis 2 (equational division): where sister chromatids separate
This results in 4 daughter cells with unreplicated chromosomes
What are the 4 stages of meiosis 1?
-prophase 1
-metaphase 1
-anaphase 1
-telophase 1 and cytokinesis
Describe the changes that a cell undergoes during prophase 1 (6)
Chromosomes begin to condense
Homologous chromosomes pair up with genes in alignment (synapsis)
Crossing over occurs between non-sister chromatids at a region called chiasmata and an exchange of DNA Segments occurs
Each pair of Chromosomes arrange as a group of four chromatids (tetrad)
Centromeres move, spindle begins, nuclear envelope breaks down, nucleoli disappear
Microtubules from one pole attach to both kinetochores of one homologue and move towards the metaphase plate
Describe the changes in metaphase 1
Microtubules attached at kinetochore. Chromatids along to form metaphase plate
What happens in anaphase one
Sister chromatids are separated and each are pulled by the microtubules to the poles Thus the homologous chromosomes are separated
Compare mitosis and meiosis
Mitosis:
Ploidy
Cytokineses once
Two final cells
Clones
Asexual reproduction, growth & repair, development
Meiosis:
Diploid to haploid
Cytokinesis twice
Four end cells
Unique genetically because of synapsis & crossing over
Gamete production
What three events are unique to meiosis?
Prophase 1: synapsis and crossing over (homologous chromosomes physically connect and exchange
Metaphase 1: at metaphase plate, there are paired homologous chromosomes (tetrads)
Anaphase 1: homologous chromosomes separate rather than sister chromatids
What are mutations?
Changes in organisms DNA and are responsible for genetic diversity
