Unit 1 - Active Recall Flashcards
Explain what you know about meiosis?
- meiosis yields 4 haploid cells
- maintains the level of DNA in sexually reproducing organisms
- yields haploid cells that are genetically different from one another
- yields genetic combinations different from the parent(s)
Explain crossing over in Meiosis I and II.
- physical exchange of genetic material among non-sister chromatids
PROCESS
1. Meiosis I
- metaphase I: homologous pairs line up on metaphase plate
- anaphase I: centromeres DON’T split, and homologous pairs move to the poles (different from mitosis)
- Meiosis II
- metaphase I: single chr. line up on metaphase plate
- anaphase I: centromeres DO split, and there is physical separation of sister chromatids (similar to mitosis)
Note:
- DOES shuffle the alleles of genes on the same chromosome (leading to new combos)
Explain independant assortment of chromosomes into gametes in Meiosis.
- occurs between paternal and maternal chromosomes
- pairs align independently of each other on the metaphase plate
- yields different combos of chromosomes within haploid sets of gametes
- # of possible combos = 2^n
Note:
- does NOT shuffle the alleles of genes on the same chromosome
Why is the shuffling of alleles important?
contributes to genetic diversity and new combinations of traits.
Explain the phases of the cell cycle in order: G0, G1, S, G2 and M.
G0
- Cells are not actively preparing to divide (have exited the cell cycle until recieve stimulus)
- No more DNA replication or cell division happens at this phase.
- Cells that never or rarely divide remain in Go permanently.
G1
- first stage of interphase is the G1 phase (first gap), the growing phase.
- cell grows and accumulates the building blocks of chromosomal DNA and the associated proteins
- increase in size and produce organelles.
S
- DNA replication occurs, and centrioles replicate (two centrosomes give rise to the mitotic spindle)
- At the center of cell, the centrosomes associate with a pair of centrioles (organize cell division)
G2
- cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation
- cell prepares for division (having double the DNA and again increase in size)
- some cell organelles are duplicated, and the cytoskeleton is dismantled to provide resources for the mitotic phase
M
- Following the interphase, the cell enters the multistep mitotic phase, where cell nucleus divides
- cell components split into two identical daughter cells.
Name some similarities or differences between mitosis and meiosis?
(-) in mitosis prophase chromosomes have no associations, while in meiosis prophase I, homologous chromosomes pair up
(-) in mitosis metaphase chromosomes line up in a single line while in meiosis metaphase I, they line up in pairs
(-) in mitosis anaphase centromeres split while in meiosis anaphase I centromeres don’t split (it would cause chr. count to go down by half)
(+) in both mitosis and meiosis metaphase, metaphase II, anaphase and anaphase II, chromosomes are in a single line then centromeres split to restore 1:1 relationship between the DNA and chromosomes.
Types of genes?
- Protein-coding genes
- RNA-encoding genes
- Regulatory signal genes
Genetic information is encoded by _____________________, and that information is transmitted
to the next generation via ____________________
genes on chromosomes, haploid gametes
Describe the principle of segregation.
- The principal of segregation refers to the process that affects allelic variation AT A SINGLE LOCUS (a single gene).
- An individual organism possesses two alleles for any particular trait, and these two alleles segregate (separate) such that each is transferred to its own gamete (see your text for further definition). The transfer of alleles to gametes occurs with equal probability.
Describe the principle of independent assortment.
alleles at different loci (on different
chromosomes) segregate independently of each other.
What ratios do you need to remember for monohybrid crosses? (single locus - both heterozygous)
Ex: Aa x Aa
Genotype ratio: 1:2:1
Phenotypic ratio: 3:1
What ratios do you need to remember for monohybrid crosses? (single locus - heterozygous/homozygous)
Ex: Aa x aa
Genotype ratio: 1:1
Phenotypic ratio: 1:1
What ratios do you need to remember for dihybrid crosses? What about if there’s two loci (AaBb x AaBb or AaBb x aabb)
Genotype ratio: 1:1:1:1
Phenotypic ratio: 9:3:3:1
Case of AaBb x AaBb
Genotype: depends
Phenotype: 9:3:3:1
Case of AaBb x aabb
Genotype: depends
Phenotype: 1:1:1:1
What are the generic forms of a test cross between homozygous recessive x unknown genotype for 1, 2 and 3 loci?
1 locus: rr x Rr (or RR)
2 loci: rr yy x R_Y_
3 loci: rr yy pp x R_Y_P_
Explain generally locus-specific notation for human ABO blood group?
Phenotype: Type O, Type A, Type B, Type AB
Genotype: ii, I^A I^A or I^A I^I, I^B I^B or I^B I^I, I^A I^B
Notes:
- three main alleles at a single locus (other rare variants do exist)
- locus encodes glycosyltransferase enzyme
- i allele is recessive to IA and IB alleles (i encodes non-functional protein)
- i form does not modify the basic blood antigen structure
- IA and IB alleles produce different variants of basic blood antigen structure
Compare and contrast dominance and epistasis.
Dominance:
1. one allele “masks” affect of other allele at same locus
2. no interactions between alleles at different loci
3. each gene (locus) affects phenotype independently (9:3:3:1)
Epistasis:
1. allele at one locus “masks” affect alleles at a different locus
2. interactions between alleles at different loci
3. this can alter Mendelian ratios (ex: alters (9:3:3:1 to be 9:3:4)
Compare dominant and recessive epistatic alleles. Example: Aa x Bb is from Lecture 3 (2/3) - Epistasis
“A” is a dominant epistatic allele:
1. “A” allele “masks” affect alleles at the same locus (A>a)
2. “A” allele “masks” affect alleles at different locus (A epistatic to B and b)
3. this will alter Mendelian ratios (12:3:1)
“a” is a recessive epistatic allele:
1. “a” allele gets masked by “A” allele at the same locus (A>a)
2. “a” allele masks affect alleles at different locus (a epistatic to B and b)
3. this will alter Mendelian ratios (9:3:4)
Compare duplicate dominant and recessive epistatic alleles. For duplicate dominant the P generation is: AABB x aaBB, for the duplicate recessive the P generation is: aaBB x AAbb.
Both “A” and “B” alleles are dominant epistatic (duplicate):
- Allele A is dominant to a (same locus)
- Allele B is dominant to b (same locus)
- Allele A & B are epistatic (masks) to a and b (different locus)
- 15 : 1 ratio
Both “a” and “b” alleles are recessive epistatic (duplicate):
- Allele a is recessive to A (same locus)
- Allele b is recessive to B (same locus)
- Allele a is epistatic to (masks) B, and b is epistatic to (masks) A
- 9 : 7 ratio
To recap, what are all of the forms of ratios that will be produced from original 9:3:3:1 ratio based on epistasis?
- recessive epistasis (9:3:4)
- dominant epistasis (12:3:1)
- duplicate dominant epistasis (15:1)
- duplicate recessive epistasis (9:7)
Human males are called the “heteorgametic sex” because?
they produce two “kinds” of haploid gametes (having X or Y chrom.)
