Flashcards in Lecture 2 Deck (93):
Genetic variations is a consequence of _________.
Meiosis (crossing over)
How many pairs of chromosomes in human cells?
23 pairs = 46 chromosomes
How many possible combinations of chromosomes in one human gamete?
2^23 = 8 million
Possible combinations of chromosomes as a consequence of sexual reproduction?
2^23 X 2^23 = 70 trillion
Inherited factor (region of DNA) that helps determine a characteristic
One of two or more alternative forms of a gene.
Specific place on a chromosome occupied by an allele
Set of alleles possessed by and individual (i.e. Rr, rr, RR)
The physical appearance or manifestation of a characteristic
Does the phenotype always match the genotype?
No, the genotype does not always match bc of recessive alleles.
Rr = Non-red hair
RR = Non-red hair
rr = Red hair
An indiv organism possessing two diff alleles at a locus
An indiv organism possessing two of same alleles at a locus
Characteristic or character
An attribute or feature possessed by an organism
What happens during Interphase?
Chromosome replication phase
In general, what happens during Meiosis I
Separation of homologous chromosome pairs
Reduction of chromosome number by half
In general, what happens during Meiosis II?
Separation of sister chromatids (equation all division)
Before Meiosis I, is the parents cell haploid of diploid?
After Meiosis I are the daughter cells haploid or diploid?
After Meiosis II?
B4 Meiosis I - Diploid
After Meiosis I - Haploid
After Meiosis II - Haploid
How much of DNA in daughter cells after Meiosis I and II compared to parent cell?
Parent - 4x DNA
Meiosis I daughter cells (2) - 2x DNA
Meiosis II daughter cells (4) - 1x DNA
1. Diploid cells have ____ chromosomes.
2. Haploid cells have ____ chromosomes.
Homologous pairs of chromosomes
Similar but NOT identical chromosome
Carry same genes in same order, BUT alleles for each trait may be different
Point on a chromosome by which it is attached to a spindle fiber during cell division
Binds homologous chromosomes together
Either of the two daughter strands of a duplicated chromosome that are joined by a single centromere and separate during cell division to become individual chromosomes
Independent centromere = ?
Shared centromere = ?
Independent centromere = chromosome
Shared centromere = sister chromatids
Replication of homologous chromosome produces __________.
Close pairing/binding of homologous chromosome
Closely associated four-sister chromatids of two homologous chromosomes
How a tetrads significant to genetic variation?
Close association of tetrads with each other cause crossing over/recombination
Exchange of genetic material btw homologous chromosomes and results in the shuffling of genes along the chromosome
Matching regions on homologous chromosomes break and then reconnect to the other chromosome
What is the significance of crossing over to genetic variation?
Causes unequal exchange of genetic info, producing chromosomes with deleted or duplicated regions
Chromatids held together by the centromere are no longer identical
After meiosis II, Some daughter cells receive chromosomes w/ recombined alleles
Offspring have diff set of alleles and genes than parents do
----> Genetic variation
What does meiosis produce?
A. Haploid gametes
B. Diploid gametes
C. Diploid cells
D. Haploid cells
Can normal separation of chromosomes occur w/o crossing over?
No, crossing over is necessary to the proper separation of chromosomes.
What stage(s) of meiosis can crossing over take place
Chromosomes begin to condense
Late Prophase I
Homologous chromosomes pairs synapse
Nuclear membrane breaks down
Crossing over takes place
What can happen to chromosomes in Prophase as a result of stress/loss of nuclear membrane?
Chromosomes can break
Homologous pairs of chromosomes line up along the metaphase plate
Homologous chromosomes separate and move toward oppo poles
Chromosomes arrive at the spindle poles
What is different about length of time in Prophase II than time in Prophase I?
Prophase II is much shorter than Prophase I
Nuclear envelope disintegrates
Indiv chromosomes line up along Equatorial/metaphase plate
Sister chromatids separate and toward oppo poles
Chromosomes arrive at the spindle poles
Product of Meiosis II
4 haploid gametes
Fertilization is fusion of _______ gametes.
How has high genetic variation in humans been an evolutionary advantage?
Many possible combination of genes
Allow many diff ways for the survival of humans and success in natural selection
Crossing over is proportional to ________
Proportion to distance of crossing over allows us to creat what?
A physical map of the chromosome
# of possible combinations of chromosomes in gametes depending on how chromosomes align and separate during meiosis I and II?
What is true about the newly formed cells from meiosis?
A. They are genetically different from one another but are the same genetically as the parent cells
B. They are genetically the same as one another and the parent cells
C. They are genetically the same as one another but are diff genetically from the parent cells
D. They are genetically different from one another and the parent cells
Which of the following takes place in meiosis II, but not in meiosis I?
A. Crossing over
B. Contraction of chromosomes
C. Separation of homologous chromosomes
D. Separation of chromatids
What is key to behavior of chromosomes in mitosis and meiosis?
Protein complex that holds the chromatids together
What signals breakdown of cohesin for separation of chromosomes?
Why must Separin signaling be complex?
In meiosis I, Separin must signal Cohesin to breakdown at the chromosome arms to allow pairs of homologous chromosomes to separate but Cohesin must be intact at the centromere
In meisosis II, Separin signals Cohesin to break down at centromeres to allow chromatids to separate.
When does meiosis occur in animals?
Spermatogenesis - Male gametes production
Oogenesis - Female gamete production
Differences of plant meiosis from animal meiosis
Diff amounts of times in stages of life cycle
Distinct phase of life cycle spent in halpoid state
What is the difference btw meiosis in less complex plants and more complex plants?
Less complex - more time haploid
More complex - less time haploid (evolutionarily favored)
Stages of spermatogenesis and their ploidy
Primary spermatocyte (2n)
Secondary spermatocyte (n)
Stages of Oogenesis and their ploidy
Primary Oocyte (2n)
Secondary Oocyte (n)
Formed during Oogenesis from the in completes cytoplasm/organelle separation
Why is ovum larger than the sperm?
Get more DNA from Mom
Get Mitochondrial DNA from Mom but NOT Dad
Can horses and donkeys interbreed even though they are diff species and if so how?
Yes, they are close enough genetically that a sperm and egg can complement each other enough to allow for meiosis
What is offspring of horse and donkey?
Why is it sterile?
Sterile bc have odd number of chromosomes
Make unbalanced gametes that do NOT have all genetic info
Consequences of improper segregation of chromosomes during meiosis?
Down syndrome - trisomy 21
Klinefelter - XXY
Can nondisjunction occur with any chromosome other than chromosome 21?
No, nondisjunction of other chromosomes are fatal and the fetus will not be viable
Passing on of physical or mental characteristics genetically from one generation to another
The proportion of total variation btw individuals in a given popul that is due to genetic variation
Which would result in red hair?
A. Wild type MC1R gene
C. 1 copy of MC1R amino acid variant
D. 2 copies of MC1R amino acid variant
Why does the MC1R with amino acid variants result in red hair?
MC1R encodes the melanocortin 1 receptor
If have one copy of variant MC1R, this reduces receptor efficiency, causing the pathway to shift to pheomelanin production
If have 2 copies, pheomelanin is predominant pigment over enumerating (brown hair), which results in red hair
A locus (or region) of DNA that encodes a functional RNA or protein product
An alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome
Which amino acid is substituted in the the MC1R protein in red heads?
Cysteine is substituted for and Arginine (R)
What other trait does having the two MC1R variants cause?
Sensitivity to anesthetics
Why did Mendel choose the traits he chose to study?
Those traits developed a pattern that he could study and create a mathematical description for.
Chosen so that crossing over had no effect on study
Mono hybrid cross
Cross btw two parents that differ In a single characteristic
Genotype: Genetic constitution of an indiv
Phenotype: Set of observable characteristics of an indiv from the interaction of its genotype with the environment
4 Conclusions from monohybrid cross
1: One character is encoded by two genetic factors (alleles)
2: Two alleles separate when gametes are formed
3: The concept of dominant and recessive traits
4: Two alleles separate with equal probability into gametes
Alleles are identical (RR or rr)
Pair of diff alleles
One dominant and one recessive (Rr)
Principle of segregation (Mendel's First Law)
Each indiv diploid organism possesses two alleles for any particular characteristic and only one is passed to offspring
Alleles segregate independently when gametes are formed
The concept of Dominance
When two diff alleles are present in a genotype, only the trait encoded by one of them, the "Dominant" allele,is observed in the phenotype. The other allele is recessive.
What type of cross demonstrates the principle of segregation?
Chromosome Theory of Inheritance
Inheritance patterns may be generally explained by assuming that genes are located in specific sites on chromosomes
Two alleles of a genotype are located on:
A. Sister chromatids
B. Homologous chromosomes
When do chromosomes replicate?
A. S Phase
B. M phase
C. Replicating phase
D. G1 phase
When can crossing over occur?
A. Metaphase I
B. Telophase II
C. Interphase I
D. Prophase I
What increases the likelihood of a cross over event occurring?
Increased distance between genes (farther apart)
Used to predict the outcomes of genetic crosses
How was the theory of inheritance tested
Back cross - cross F1 generation with Parent
If don't know anything about parents genotype what is normally done?
Cross the unknown parent with a homozygous recessive
High probability of seeing recessive phenotype:
- Either 100% recessive phenotype
- Or 50/50
If an F1 plant (round seeds, heterozygous) is back crossed to the parent with round seeds (homozygous), what portion of progeny will have wrinkled seeds?