Unit 5: Heredity Flashcards
Asexual Reproduction
Produces clones (genetically identical)
Single parent
Little variation in population - only thru mutations
Fast & energy efficient
Eg. budding, binary
fission
Sexual Reproduction
Meiosis produces
gametes (sex cells)
2 parents: male/female
Lots of variation/diversity
Slower & energy
consumptive
Eg. humans, trees
Role of Meiosis in passing traits from parent -> offspring
It’s a process that divides these 46 chromosomes into two sets of 23 each (in separate cells). Therefore, a mother passes 23 chromosomes (and all their genes) to her offspring, the father contributes 23 more (with their genes), so the child winds up with 46 chromosomes and the genes of both parents
Role of Fertilization in passing traits from parent -> offspring
combines (sperm & egg) gametes to form a zygote, which is the start of biological reproduction & divides by mitosis to form multicellular diploid organism
Meiosis Main idea
Cells divide TWICE
Result: 4 daughter cells w/ 1/2 as many chromosomes (46->23) than parent cell (each has one chromosome)
Meiosis 1 = 1cell->2cell
Meiosis 2 = 2cell->4cell
Meiosis 1 Interphase 1
Chromosomes replicate (double up like S phase)
Meiosis 1 Prophase 1
2 sets of chromosomes 1 from each parent
Synapsis: Homologous chromosomes (same) pair up (double fingers touching)
Forms tetrad (4 sister chromatids)
CROSSING OVER/RECOMBINATION (Chiasmata): chromatids from each homologous chromosome exchange allele segments (RANDOM) ->sometimes diff gene combos
Meiosis 1 Metaphase 1
Homologous chromosomes line up at equator & attach to spindle fibers opposite poles (tetrads)
(2 double hand fingers one on top of other)
independent assortment occurs , chromosomes line up independently of one another, both maternal & paternal chromosomes gets passed down to each
Meiosis 1 Anaphase 1
Pairs of Homologous chromosomes separate (BUT sister chromatids still attached by centromere) (2 double fingers stay together but hands pull apart a bit)
Telophase & Cytokinesis
Diploid Parent Cell eventually splits into 2 haploid cells (one chromosome per cell)
Each chromosome = 2 sister chromatids
IN SOME species, chromatin & nucleus reform
Meiosis 2 Prophase 2
No interphase
No crossing over
Spindle forms
Meiosis 2 Metaphase 2
Chromosomes line up in center of cell
Meiosis 2 Anaphase 2
Sister chromatids separate (NOW two fingers split into just four separate fingers)
Meiosis 2 Telophase 2
creates 4 Haploid cells (has HALF DNA, ONE chromosome, & only ONE chromatid)
3 Ways Meiosis is Different than Mitosis
1) Prophase 1: Synapsis & Crossing over
2) Metaphase 1: PAIRS of homologous chromosomes line up on metaphase plate
3) Anaphase 1: Homologous pairs separate -> sister chromatids still attached at centromere
How the chromosome number is reduced from diploid to haploid in meiosis
During meiosis, the parent cell starts out being diploid. After the 1st meiosis, the homologous chromosomes are separated & the cell is split into 2 haploid cells with each chromosome consisting of two chromatids. After the 2nd phase, the two sister chromatids get split so that the end result is four haploid (23 chromosomes or one in each cell) .
Importance of homologous chromosomes to meiosis.
Homologous pairs = important bc they allow for recombination, crossing over & random segregation into new cells (recombinants). Thus allowing for genetic variation among organisms. Unlike in mitosis where the daughter cells are genetically identically to the parent cells.
Independent assortment
Random orientation of homologous chromosome pairs in Metaphase 1
ex: blue homologous pair chromosome on top red pair
or blue on blue, red on red
Crossing Over
Exchange genetic material
recombinant chromosomes
Random Fertilization
Any Sperm w/ any egg
lots of diff combos
Importance of crossing over, independent assortment, & random fertilization to increasing genetic diversity
Crossing over, independent assortment & random fertilization allows for unique combination of gene.
In crossing over, chromosomes w/ new combinations of genes are created when sections of chromosomes are interchanged.
Independent assortment results in the production of unique gametes since alleles of two (+) different genes get sorted into gametes independently of one another. the allele a gamete receives for one gene does not influence the allele received for another gene. the chromosome inherited from either father or mother can sort into any gamete
Random fertilization, any egg can be fertilized by any sperm, this leads to millions of different possible combinations.
Gene Vs. Allele
Gene: a unit of genetic info codes for specific protein/RNA
Allele: (alternate version/variations of gene) could lead to diverse traits/characteristics expressed such as eye color.
P means
parental generation
F1 means
First Gen
F2 means
Second Gen
Law of Segregation
2 alleles for each character/trait
separate during gamete formation. only one allele (ex: hair color) present in each gamete
Nature VS. Nurture
Both genetic & environmental factors influence phenotype
ex: can affect gene expression, mutation in enzyme that catalyzes gene expression but does not directly affect genotype
Phenotype plasticity
ability of individual genotypes to produce different phenotypes when exposed to different environmental conditions
How the chromosome theory of inheritance connects
the physical movement of chromosomes in meiosis to
Mendel’s laws of inheritance
Segregation: 2 alleles for each character separate during gamete formation (meiosis anaphase 1)
Independent assortment: each pair of alleles segregates/separates independently during gamete formation
talks about how homologous chromosomes also undergo independent assortment & segregation during meiosis that allows for the genes to do their own separation
Chromosome Theory of Inheritance
Genes have specific loci
(positions) along
chromosomes
Chromosomes undergo
segregation &
independent assortment
Sex-Linked Genes
Females (XX), male (XY)
Eggs = X, sperm = X or Y
Fathers pass X-linked genes TO DAUGHTERS, but not sons
Males express recessive trait on the single X (hemizygous)
Females can be affected or carrier
Females may pass trait to all sons bc only have one x
Barr Body
inactive X chromosome; regulate gene
dosage in females during embryonic development
Linked Genes
Genes located near each other on same chromosome
tend to be inherited together
Genetic Recombination:
production of offspring w/ combination of traits different from either parent
If offspring look like parents = parental types
If different from parents = recombinants
Recombination
Frequency
Recombinants/Total # Offspring x 100%
Crossing Over
explains why some linked genes
get separated during meiosis
The further apart 2 genes on same chromosome, the
higher the probability of crossing over and the higher
the recombination frequency
Linkage Map
genetic map that is based on % of crossover events
1 map unit = 1% recombination frequency
Express relative distances along chromosome
50% recombination = far apart on same chromosome or on 2 different chromosomes
Genomic imprinting
phenotypic effect of gene depends on whether from M or F parent
Mendelian inheritance says that all genes are passed on BUT with imprinting one set of DNA isn’t considered
Methylation:
silence genes by adding methyl groups
to DNA
Maternal Inheritance
In animals:mitochondria
transmitted by the egg NOT sperm
In Plants: chloroplasts & mitochondria transmitted by ovule not pollen,
We all share the same mitochondrial DNA as our mothers; in Mendelian inheritance our mitochondria would have a mix of our paternal and maternal DNA
how can the alteration of chromosome number or structurally altered chromosomes cause genetic disorders?
Nondisjunction occurs when the members of a pair of homologous chromosomes do not separate properly during meiosis 2. As a result, one gamete will receive two copies of a chromosome and one gamete will not receive any. Errors in meiosis or damaging agents such as radiation can cause portions of a chromosome to be lost or rearranged, causing mutations.
How are genomic imprinting and inheritance of mitochondrial DNA exceptions to standard Mendelian inheritance?
Genomic imprinting is a phenomenon in which expression of an allele in offspring depends on whether the allele is inherited from the male or female parent. It occurs during gamete formation and results in the silencing for a particular allele of certain genes. The offspring only expresses one allele of an imprinted gene (thus being an exception to Mendelian inheritance). Genes present in the mitochondria are only inherited from the mother because the zygote’s cytoplasm only comes from the egg.
Nondisjunction
chromosomes fail to separate properly in Meiosis I or Meiosis II
Nondisjunction of homologous chromosomes in Meiosis 1
Daughter cells: n+1, n+1, n-1, n-1
Nondisjunction of homologous chromosomes in Meiosis 2
Daughter cells: n+1, n-1, n, n
Aneuploidy
abnormal # chromosomes
Monosomic (1 copy = 2n-1) (absence of one member of a chromosome pair(45 instead of 46)
Trisomic (3 copies = 2n+1) (ex: 3 #21 chromosomes)
Polyploidy
2+ complete sets of chromosomes
triploid (3n) (69 per cell) chromosomes) or tetraploid (4n) (92 per chromosomes per cell)
rare in animals, frequent in plants (wheat, strawberries)
Chi-Square Test
if BIGGER CAN reject null hypothesis
if SMALLER than critical value CANNOT reject null hypothesis
If two heterozygous traits are crossed what is the phenotype ratio
9/16, 3/16, 3/16, 1/16
Total9/16= Outcome
Total3/16= Outcome(x2)
Total*1/16=Outcome
(Outcome-Expected^2)/2 for each & add up
true breeding
homozygous for genes
