Offspring are genetically identical to original cell or organism
Involves inheritance of all genes from one parent
Asexual reproduction produces new cells in order to ..???
produce new unicellular cells
heal wounds and replace damaged cells/tissues
grow and develop
what are mostly sexual
What are mostly asexual
Asexual reproduction - cell replication ='s
- only one parent cell
- offspring are genetically identical to parent
- DNA replicated and evenly divided so 2 daughter cells get same DNA, TWO copies of each gene ='s Mitosis
Sexual reproduction ='s
- offspring are genetically different from one another and from parents
- Gamete are combinded from two parents
- DNA replicated and divide up so each of 4 daughter cells gets ONE copy of each gene ='s MEIOSIS
Genetic Variation in Population='s
Shuffling of gene forms (alleles)
DNA from two parents ='s
random gamete fusion, mating choice
How many chromosomes does a person have ??
Life cycles of sexually reproducing organisms involve....??
alternation of haploid and diploid stages
Some life cycles include longer ______ phases and longer ____phases???
Longer diploid and haploid phases
In most animals _______ state dominates
When the Diploid statedomintate what happens to the Zygote
Zygote first undergoes mitosis to produce diploid cells
What happens later in the life cycle to diploid cells??
Diploid cells undergo meiosis to produce haploid gametes
What do Gametes do when they combine??
Gametes combine to regenerate diploid zygote
What are the products of Mitosis??
- Diploid cells
- 2 copies of each autosome (1-22)
- 2 sex chromosomes: 2X or (1X +1Y)
What are the products of Meiosis???
- Haploids cells
- 1 copy of each autosome (1-22)
- 1 sex chromosome: 1X or 1Y
specialized form of cell division in gonads to produce gametes
What does gametogenesis reduce??
Reduces number of chromosomes in each cell by one-half.
In Gametogenesis chromosomes come in ??
Human somatic cells have 22 pairs of autosomes, and one pair of sex chromosomes (2X or X+Y)
human gametes have one of each pair (22 autosomes plus 1X or 1Y)
What are the 4 phases in Meiosis I
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
What happens in Prophase I
homologous pairs come together
What happens to Metaphase I
homologous pairs line up at equator
what happens in Anaphase I
homologous pairs separate
What happens in Telophase I
nuclear envelope reforms
Meiosis II occurs when
after an nterval of variable length
What is the difference between Anaphase I in Meiosis I and Anaphase in Mitosis
in Anaphase I Microtubules pull homologous chromosomes apart and sister chromatids are held together
In Anaphase in Mitosis microtubules pull sister chromatids apart
What is the difference in Metaphase I in Meiosis I and Metaphase in Mitosis
- Metaphase I:
- -Chiasmata hold homologues together
- -the kinetochores of sister chromatids fuse and function as one
- -microtubules can attach to only one side of each centromere
- -Homologues do NOT pair
- -kinetochores of sister chromatids remain separate
- -microtubules attach to both kinetochores on opposite side of centromere
What is the Final result of meiosis
- -Four cells contain haploid sets of chromosomes
- -in animals, develop directly into gametes
- -in plants, fungi, divide mitotically
- -produce greater number of gametes
- -Adults with varying numbers of gametes
What does Genetic Variation in Population mean??
Shuffling of gene forms (alleles)
What happens when you get DNA from two parents
random gamete fusion, mating choice
What happens Early Prophase I
Homologous chromosomes closely associate (sunaptonemal complexes)
exchange of equivalent portions of chromosomes between members of a homologus pair
What does Crossing over result in ???
Results in new types of gametes being formed
What is the Crossing Over Process in Prophase I ??
- 1. Homologous chromsosome
- 2. Chiasma (non sister chromatids join at chiasmata)
- 3. Recombinant chromatids
- -alleles of genes that were formerly on separate homologues can now be found on the same homologue
What does Genetic Recombination =???
='s production of new combinations ofalleles due to crossing over
Crossing Over ='s
- -phrophase I: homologous pairs exchange genetic information
Random alignment -----> ______???
- Independent Assorment
- - Metaphase I
What is Metaphase 1
radom alignment of homologue, which homologue goes to which cell
What are the Key points in Meiosis??
- 1. Synapsis and crossing over
- 2. sister chromatids remain joined at their centromeres throughout meiosis I
- 3. Kinetochores of sister chromatids attach to same pole in meiosis I
- 4. DNA replication is suppressed btw meiosis I and Meiosis II
What happens in Nondisjunction ??
- -Chromosome pairs fail to separate during meiosis I
- - Chromosomes fail to separate at centromere during meiosis II
- -gametes with incorrect chromosome number
- -zygote with incorrect chromosome number
Accidents in meiosis can alter chromsome number
Failure of homologues or sister chromatids to separate properly during meiosis
Who is at risk for Nondisjunction??
- -increased incidence of trisomic embryos in older women
- -Meiosis begin in all eggs b4 the woman is born, and finishes as each egg matures in the monthly cycle following puberty
- -Eggs of older women have been "within" meiosis longer
gain or loss of chromosome
Loss of chromosome
Gain of chromosome
Why do we typically only see trisomy 13, 15, 18, 21, and 22 births??
Some of the smalles autosomes can present as 3 copies and allow individuals to survive
- -13,15,18- severe defects, die w/in a few months to year
- -21 and 22- can survive to adulthood
What does an extra copy of a chromosome 21 cause??
Trisomy 21: 3 copies of chromosome 21
most common human chromosome abnormality (1/700 births)
What does an extra copy of Chromosome 18 cause??
- Trosomy 18: 3 copies of chromosome 18
- -1/3,000 births
- - incidence increases w/ maternal age
- -50% are stillborn, 5-10% live to 1 year, 1% live to 10 years, rare to survive to adult
What happens when there is an extra copy of chromosome 13??
- Trisomy 13: 3 copies of chromosome 13
- -incidence increases w/ maternal age
- - 18% survive beyond 1 year, rare to survive to adult
Nondisjunction of sex chromosomes generally do not experience ______???
Do not generally experience severe developmental abnormalities
Individuals have somewhat abnormal features, but often reach maturity and in some cases may be fertile
What are examples on Nondisjunction of sex chromosomes??
- XXX-triple X females
- XXY-males (Klinefelter syndrome)
- XO-females (Turner syndrome)
- OY-nonviable zygotes
- XYY- males (jacob syndrome)
Males (klinefelter syndrome)
females Turner Syndrome
Males Jacobs syndrome
Chromosomal abnormalities result from errors in ______???
meiosis, mitosis, DNA replication, environmental damage
What are breakages and rejoining of chromosome segments called???
Breakage and rejoining of chromosome segments can cause ...???
Gametes: birth defects/spontaneous abortion
Somatic cells: cancer