Chapter 13 Flashcards
What is hereditary?
transmission of traits from one generation to another
What is variation? (2)
reason identical copies from parents result in differences in offspring
the pheneotype
What are genetics? (2)
the scientific study of heredity and hereditary variation
the genotype
What are genes? (2)
hereditary units containing information/DNA
Programs cells to synthesize certain enzymes or proteins
What are gametes? (3)
reproductive cells that transmit genes
male gametes- sperm
female gametes- eggs
What is the locus?
gene’s specific location on a chromosome
What is asexual reproduction?
a single individual passes its genes without fusion of gametes
What is an example of asexual reproduction, and what does it result in?
Mitotic cell division
results with a clone (genetically identical individual)
What is sexual reproduction? (2)
two parents give rise to offspring with unique combinations of genes two parents
Vary genetically from siblings and parents
What is a life cycle?
sequence of stages in the reproductive history of an organism
What us a karyotype? (2)
pairs of chromosomes arranged from the longest
The two sets of 23 types of chromosomes are put together
What are homologous chromosomes/ homologs? (2)
pair of chromosomes with the same length, centromere position, and staining pattern
both pairs carry the same genes
What are human female chromosomes?
homologs of X chromosomes
What are human male chromosomes?
XY chromosomes
What are sex chromosomes, and what do they determine?
Human X and Y chromosomes
determines offspring’s sex
What are autosomes
non-sex chromosomes
What are diploid cells? (2)
cell with two sets of chromosomes (2n=46)
n= number of chromosomes in a single set
What are haploid cells? (2)
cells with only one set of chromosomes
In humans, the haploid number is 23
What is the human life cycle? (3)
Begins with fertilization, When a haploid sperm fuses with a haploid egg and fuses their nucleus
Forms a zygote- Diploid fertilized egg
As humans develop into sexually mature adults, mitosis of the zygote and its offspring generate somatic cells
How do gametes develop and reproduce? (4)
Only cells that do not produce through mitosis
Develop from germ cells in gonads
It cannot undergo mitosis if it does, it would become diploid
Undergoes meiosis
How is significant about gamete meiosis? (3)
Reduces the number of sets of chromosomes from two to one in gametes
Prevents doubling of chromosomes
Only diploid cells undergo meiosis
How do sexual life cycles vary?
Different species have different timing of fertilization and meiosis in their life cycle
What are the three groups of sexual life cycles?
humans and most animals
alternation of generations
fungi, protists, and algae
What is the sexual life cycle of humans and most animals? (2)
gametes are the only haploid cells
Do not undergo further cell division other than meiosis prior to fertilization
What is alternation of generations? (2)
Exhibited by some algae and plants
includes both a diploid and haploid stage
What occurs during the diploid stage in the alternation of generations? (5)
AKA sporophyte
Produces haploids through miosis called spores
Spores do not fuse, but divide mitotically,
generating a haploid stage called gametophyte
gametophyte gives rise to gametes by mitosis
What occurs during the haploid stage in the alternation of generations?
During fertilization, it results in a fusion of two haploid cells into a diploid zygote
Zygote develops into next the next sporophyte generation
What occurs in the sexual life cycle of fungi, protists, and some algae? (4)
After gametes fuse and form a diploid zygote, meiosis occurs without a diploid offspring developing -
Produces haploid cells instead of gametes
Haploid cells divide by mitosis and give
rise to a descendent
The Descendent undergoes further mitosis to produce the cells that develop into gametes
What is meiosis? (3)
Consists of two consecutive cycles, Meiosis 1 and Meiosis 2
Results in four daughter cells, one chromatid each, with half the amount of chromosomes as the parents
begins with a pair of sister chromatids, one from each parent
What occurs during Meiosis 1?
Reduction division (reduces the number of chromosomes)
What occurs during Prophase 1 early stage? (6)
Centrosome moves
Spindle forms
The nuclear envelope breaks down
Chromosome condenses
Chromosomes pair with their homolog
cross over occurs
What is cross-over?
DNA molecules of chromatids are broken and rejoined with each other
What occurs during Prophase 1 middle stage?
Each pair has one or more x-shaped regions called chiasmata where crossover overs
What occurs during Prophase 1 late stage? (2)
Microtubules from one pole attach to the kinetochores
Homologous pairs will move toward the metaphase plate
What occurs during Metaphase 1? (2)
Pairs of chromosomes are now on the plate
Both chromatids are attached to kinetochore microtubules from one pole
What occurs during Anaphase 1? (3)
Proteins cleave sister chromatid cohesions along chromatid arms to separate
Homologs move toward opposite poles
Sister chromatid cohesion persists, causing chromatids to move as a unit
What occurs during Telophase 1? (3)
Each half of the cell has a complete haploid set of duplicated chromosomes
Composed of two sister chromatids
One or both chromatids include regions of non-sister chromatid DNA
What occurs during cytokinesis?
Occurs simultaneously with telophase, forming haploid daughter cells
What occurs during Meiosis 2?
Equational division- chromosomal number remains equal as haploid
What occurs during Prophase 2? (3)
Spindle forms
each chromosome still consists of two chromatids
moves towards metaphase 2 plate
What occurs during Metaphase 2? (3)
Chromosomes are positioned at the metaphase plate
Because of crossover, chromatids are genetically different
Kinetochores are attached to microtubules from opposite poles
What occurs during Anaphase 2? (2)
Proteins breakdown the cohesion of sister chromatids
Chromatids move to opposite poles
What occurs during Telophase 2? (2)
Nuclei forms
chromosomes decondenses
What is the result of meiosis? (2)
One parent cell produces four daughter cells with a haploid set of chromosomes
All genetically distinct from parent and sibling cells
What occurs during the first step of crossover? (3)
During interphase, duplicated chromatids are held by cohesins
Each homologous pairs are associated along their length
DNA molecules get broken at corresponding points
What occurs during the second step of crossover? (3)
Synaptonemal complex forms
- Zipperlike protein complex
- Attaches homologs to each other
What occurs during the third step of crossover? (3)
Synaptonemal complex fully forms
Homologs are in synapsis
DNA breaks join to corresponding breaks, crossing over
What occurs during the fourth step of crossover? (3)
Synaptonemal complex disassembles
Remains attached at cohesion
Crossover locations show up as chiasmata
What is unique to meiosis when compared to mitosis? (3)
Synopsis and cross over
Homologous pairs at metaphase
Separation of homologs
How do the sister chromatids differ in mitosis and meiosis?
In mitosis, remain together until anaphase
In meiosis, remain together until anaphase 2
Where does genetic variation arise during sexual reproduction? (3)
Independent assortment of chromosomes
Crossing over
Random fertilization
What is the independent assortment of chromosomes? (3)
Random orientation of homologous pairs at metaphase during meiosis 1
50% chance a daughter cell will get maternal chromosomes
Independent assortment- maternal and paternal homologs sort independently from every other pair
How does crossing over result in genetic variation? (3)
Produces recombinant chromosomes
Individual chromosomes carrying genes from different parents
About 1-3 crossovers occur per pair
What is random fertilization?
The fusion of the male gamete and female gamete produces a zygote with trillions of diploid combination
How does genetic variation and evolution correlate? (2)
The population evolves from the reproductive success of its variants
Sexual reproduction generated genetic diversity
