Genetics Flashcards
Diploid vs haploid organisms
Diploid: two copies of genome per cell
Haploid: one copy of genome per cell
In sequel reproduction, the diploid is produced by
The haploid of the mother and the haploid of the father fusing
Gene
length of DNA coding for a particular gene product
Locus
pinpointing a genes location on a chromosome
Human genome has how many chromosomes?
24 chromosome pairs
22 autosomes pairs and 2 allosomes pairs (sex chromosomes)
One from mom, one from dad
Homologous chromosomes
Two nonidentical copies of a chromosome
Alleles
Different versions of a gene that may carry out the genes function differently
Genotype
DNA sequence of the alleles a person carries
Heterozygote vs homozygote
Hetero: two different alleles at a given locus
Homo: two identical alleles at a given locus
Phenotype
Physical expression of the genotype
Dominant vs recessive
Dominant: expressed allele in heterozygote
Recessive: non-expressed allele in heterozygote
Can a haploid organism have recessive alleles?
No because there is only one copy of the genome
Mitosis produces:
Meiosis produces:
Mitosis prod two identical daughter cells from a parent cell
Meiosis prod one haploid sex cell from a diploid cell
Spermatogonia and oogonia
Only cells to undergo meiosis
Primary differences between meiosis and mitosis (2)
- Mitosis has one cell division to make two daughter cells and meiosis has two cell divisions to make four haploid gametes (meiosis 1 and meiosis 2)
- Recombination between homologous chromosomes occurs in meiosis
Steps of Meiosis
- S-phase: ______
- Prophase I: chromosomes condense and ______ breaks down, _____ form
- DNA is cut at the same location on homologous chromosomes, ______ between the pair and chromosomes are _____
- Metaphase I: _____ align along _____ plate
5: Anaphase I: homologous chromosomes ____ and _____ remain together
6: Telophase I: __________ (cells are now considered to be: ______ because they have one set of chromosomes but are still replicated sister chromatids) - _________ begins with the ____ process as Meiosis I except that:
- Anaphase II separates ___________, not tetrads
- Telophase II produces ________ from the single diploid parent cell
- S-phase: DNA replication
- Prophase I: chromosomes condense and nuclear envelope breaks down, tetrads form
- DNA is cut at the same location on homologous chromosomes, genes are swapped between the pair and chromosomes are realigned
- Metaphase I: tetrads align along metaphase plate
5: Anaphase I: homologous chromes separate and sister chromatids remain together
6: Telophase I: divides into two cells (cells are now considered to be: haploid because they have one set of chromosomes but are still replicated sister chromatids) - Meiosis II begins with the same process as meiosis I except that:
- Anaphase II separates sister chromatids, not tetrads
- Telophase II produces 4 haploid cells with a single chromosome that is not replicated from the single diploid parent cell
Prophase I in meiosis:
What are tetrads?
Chromosomes condense and nuclear envelope breaks down, homologous chromosomes align with each other in synapsis with the two copies of each gene on two different chromosomes brought closely together (tetrad)
Metaphase I in meiosis vs mitosis
Meiosis tetrads align at the metaphase plate
Mitosis sister chromatids align at the metaphase plate
Nondisjunction
Failure of the sister chromatids or homologous chromosomes to seperate during meiosis
If two homologous chromosomes fail to separate how many copies of the chromosomes will the resulting gametes have?
I: One will have four and the other will have none
2: Two will have two and two will have none
Trisomy and monosomy
When a gamete from non-disjunction fuses with.a normal gamete to create a zygote with either three copies of a chromosome (trisomy) or one copy (monosomy)
Mendel’s law of segregation
Two alleles of an individual are separated and passed on to the next generation singly
Mendel’s law of independent assortment
Alleles of one gene will separate into gametes independently of alleles for another gene
If G is green an g is yellow and W is wrinkly and w and smooth then G and W will be inherited independently of one another
Cross
Tool to discern genotypes by looking at the phenotypes of progeny from a cross
Pure-breeding strain
mating yellow plants with yellow plants produces yellow plants
Testcross
One individual is crossed with another that has a homozygous recessive genotype
Allows the alleles from one parent to be displayed phenotypically when the other parent is homozygous recessive
Progeny of a test cross is called the
F1 generation
Probability rules:
Rule of multiplication
Rule of addition
M: probability of BOTH event A and event B happening is the product of both their probabilities
A: probability of EITHER event A or event B is the sum of their probabilities
Incomplete dominance
Specific gene does not have one dominant gene but multiple (R for red and W for white for plant color: what would RW express? Pink)
Codominance
Two alleles are expressed but are not blended
For example blood type: IA and IB would be AB rather than a new blended product
Pleiotropism
Expression alerts many different, seemingly unrelated aspects of the total phenotype
For ex: a mutation of one gene may affect the heart, bone and inner ears
Polygenism
Complex traits that are influenced by many different genes
Penetrance
Likelihood of a person with a given genotype to express that phenotype (spectrum of options)
-Alleles, mutations, also effected
Epitasis
Expression of alleles for one gene is dependent on a different gene
(Can’t express curly hair gene if other gene says bald)
Male or female gamete determines sex of embryo?
Father because he either donates X or Y in meiosis
Sex-linked traits
Traits that are determined by genes on the X or Y chromosome because of their unique patterns of expression and inheritance
Linkage
Genes on the same chromosome may not display independent assortment
Genes close to one another on the chromosome will be inherited
Not independently
If the color and height gene display linkage is it possible to predict the possible gametes of TTgg individual? A TtGg individual?
TTgg will just be Tg despite location
TtGg cannot be predicted because on each allele could be TG, tg, tG, or Tg
Exception to linkage:
Meiotic recombination between homologous chromosomes can separate alleles located on the same chromosome
A cross involving genes on the same chromosome result will
Intermediate between linkage and independent assortment
Farther apart two genes are, ____ likely to undergo recombination
More
If genes are located far enough apart they will display
NO linkage because recombination will be so great and will assort independently
Frequency of recombination
(#recombination) / (#offspring)
Progeny
Offspring
Autosomal Recessive
2 copies of the gene are required to display the trait
No sex basis
Can skip generation
Autosomal Dominant
Single copy of the allele required for trait to be displayed
Not sex linked
Affected parent passes to all (AA) or 50% (Aa) of children
Mitochondrial traits
Inherited from mother because she passes on organelles (inc. mitochondria which has a genome)
All of affected females offspring has the trait
Individual cannot inherit mitochondrial traits from their father
A
Sex-linked traits
Traits located on the X or Y chromosome
Can a father pass a Y linked trait to his daughter?
Can males be carriers of recessive Y-linked traits without expressing them?
No
No because the Y-linked traits are carried in only one copy males will always express recessive traits on the Y chromosome
Affected father has all affected sons
Unaffected father cannot have affected son
Do women always express X-linked recessive genes?
Do men always express X-linked recessive genes?
No only express them when they are homozygous
Yes-they only have one copy
Can skip generations
SO X LINKED TRAITS AFFECT MEN MORE THAN WOMEN
X-linked dominant
Affected fathers have all affected daughters, no affected sons
Affected mothers can have unaffected sons or daughters (passes equally to sons and daughters)
Does not skip generations
Gene pool
Sum total of all genetic information in population
Henry Weinberg Law
Frequencies of alleles in the gene pool of a population will not change overtime
Assumptions that the Henry Weinberg Law assumes (5)
- No mutations
- No migration
- No natural selection
- Random mating
- Large enough pop to prevent random drift in allele frequencies
IRL: isn’t realistic
Henry-weinburg implications at the molecular level
Segregation of alleles, independent assortment and recombination during meiosis can alter the combinations of alleles in gametes but cannot increase or decrease the frequency of an allele in the gametes of one individual or the gametes of the population as a whole
p^2 + 2pq + q^2 = 1
where:
p^2=
2pq=
q^2=
p^2= frequency of the GG 2pq= frequency of the Gg q^2= frequency of the gg
Hardy-weinburg equilibrium
After one generation allele frequencies no longer change
