Unit 5: Heredity Flashcards
Somatic Cells
the cells that make up your body to allow it to live and function
* Mitosis divides these cells (doing meiosis with these = double the DNA)
Gametes/ Sex cells/ Germ Cells
the cells used for sexual reproduction, only exist to pass on genetic information
Germ cells undergo Meiosis to become sex cells/ gametes
- germ cells are diploid and undergo meiosis to become haploid gametes that are then used in sexual reproduction
Ploidy
Ploidy = the number of FULL sets of chromosomes
Diploid: 2 full sets of chromosomes (in humans’ diploid is 23 pairs and 46 total)
Haploid: one full set (gametes must be haploid to combine & be diploid)
Polyploidy: a FULL EXTRA SET of chromosomes (lethal)
Meiosis 1
- Happens within one individual
exists to REDUCE PLOIDY for sexual reproduction (ex. has 4 chromosomes, replicates and now has 4 chromosomes with centromere, Meiosis 1 pulls apart homologous chromosomes with centromeres and now daughter cells have 2 chromosomes each have 2 chromosomes with centromere) - meiosis 1 does not split the chromatids apart
Interphase: same as Mitosis (G1, S, G2)
Prophase 1: chromosomes condense, nucleus breaks down, spindle fibers form (Homologous chromosomes form TETRADS & CROSSING OVER OCCURS)
Metaphase 1: spindle fibers arrange pairs of homologous chromosomes on the equator
Anaphase 1: fibers split CHOMOSOMES apart (xx = x)
Telophase 1: cells reform, Nucleus reforms DNA condenses
*** Meiosis 1 reduces Ploidy (Turn Diploid into Haploid)
- only reduced here, not in Meiosis 2
Meiosis 2
- No interphase between Meiosis
Prophase 2: chromosomes condense, nucleus breaks down, fibers form
Metaphase 2: spindle fibers arrange chromosomes (sister chromatids) in middle
Anaphase 2: spindle fibers pull SISTER chromatids to opposite poles
Telophase 2: chromosomes decondense + cytokinesis happens
END RESULT: 4 genetically unique haploid daughter cells
Crossing Over
occurs during PROPHASE 1 and creates new combinations of genetic material (infinite # of possible combinations)
- one way to ensure genetic diversity
- DNA can switch in many different ways (no way to predict how it will switch)
Law of Segregation
Another way to ensure genetic diversity
2 alleles for given genotype will be segregated randomly into gametes (parents donate ONE allele per gamete)
Law of Independant Assortment
Third way meiosis ensures genetic diversity
homologous chromosomes will be sorted into gametes independently of each other (genes on one DO NOT affect the inheritance of another gene on a chromosome)
Nondisjucntion
main mistake during MEIOSIS
- the failure to properly separate genes during Anaphase 1 or 2
Leads to ANUPLOIDY: cells with wrong number of chromosomes
- trisomy: more (47)
- monosomy: less (45)
*It is the # of chromosomes not an additional set like polyploidy
Visual representation with a Karyotype
Gregor Mendel
the father of genetics who figured out all of this w/o knowledge of genes (used pea plants in 1800’s)
created the:
- Law of Dominance
- Law of Segregation
- Law of Independant Assortment
patterns for autosomal traits/Gregorian traits
Allele
a version of a gene (usually two variations Dominant and Recessive)
- parent only donates 1 allele to offspring
Genotype vs phenotype
Genotype: the combination of alleles in an individual
(AA, Aa, aa)
Phenotype: the physical expression of a trait
(aa = blue, Aa = brown, AA = brown)
Homozygous vs Heterozygous
Homozygous = having 2 of the same alleles
- Must specify if it is dominant or recessive
Heterozygous: having 2 different alleles (Aa)
- don’t need to specify
True Breeding
2 parents reproduce and offspring are the same as parent (homozygous, purebred)
P, F1, F2, F3… Generation
P generation: parental generation, first reproduction in the family (not just the parents of the offspring you are looking at)
F1 generation: filial generation, offspring from previous generation
F2 offspring of F1, F1 offspring of P etc.
Test Cross
technique when organism of unknown genotype is crossed with recessive homozygous individual (results in ratio that tells us the genotype of parent)
Law of Dominance
Some genes have 2 alleles, one is dominant, one is recessive. Hybrid individuals have the dominant phenotypes
Probability
Probability of two mutually exclusive events occurring: A OR B occurs, not both
- p(a) + p(b) OR = ADD
Probability of two independent events (two things happen): results of one don’t affect results of another
- p(a) x p(b) * AND = MULTIPLY*
Monohybrid cross
Both parents are heterozygous for ONE trait (same trait)
= Aa x Aa
- 3:1 phenotype (25% AA, 25% aa, 50% Aa)
Dihybrid cross
Both parents are heterozygous for BOTH traits
= AaBb x AaBb
- for simple Mendelian traits 9:3:3:1 phenotypic ratio
(9 dom-dom, 3 rec- dom and dom - rec- 1 rec-rec)
FOIL method AaBb
AB, Ab, aB, ab
Punnett Square and Multigene genetics
Punnett Square: visual representation of probability of outcomes of reproduction (each parent donates one allele (crosses genotypes)
Multigene Genetics: parents donate one allele per gene
First - determine possible allele combos from each parent
- FOIL method (just distribute)
Second - use ALLELE COMBINATIONS in a Punnett square
* If allele combos repeat you can cut out those rows
Chi-squared Test
way to tell if something is statistically significant
Null hypothesis = results (variations) are due to random chance
Alternitive hypothesis = results aren’t due to chance, something else is affecting them
First: determine degree of freedom (# of possible outcomes - 1)
Second: x^2 = the sum of observed - expected squared divided by expected E (o- e)^2/ e
Third: use p- value (.05 unless explicitly mentioned) to determine critical value
*if x2 is greater than critical value = REJECT THE NULL, RESULTS NOT DUE TO CHANCE
- if x2 is less then critical value = FAIL TO REJECT NULL, RESULTS DUE TO CHANCE
Pedigrees
family tree shows genetic traits over multiple generations
square = male
circle = female
diamond = unknown sex
filled in = affected
half filled = carriers
unfilled = unaffected
solid line = mating
- affected trait can be dominant or recessive so pay attention to how it works
Autosomal Chromosomes
the first 22 pairs of chromosomes that EVERYONE AUTOMATICALLY GETS
- based on size, 1 is largest, 22 is smallest
Sex Chromosomes
23rd pair of chromosomes that determine the biological se of the offspring
- females = xx
- males = xy
50% chance male or female for each offspring
- X chromosome is LARGE and contains necessary information for survival
- Y chromosome is small and only contains codes for male reproduction organs
Sex linked traits (x linked traits)
-decided by the genes on the x- chromosome
- for sons to have the trait, the mom MUST HAVE IT
- for daughters to have recessive trait, DAD MUST HAVE IT
- males CANNOT be heterozygous, they either have it or they don’t b/c they only have 1 x chromosome
ex. xA y normal, xa y colorblind - more likely to be seen in males
- females are more normal bc XA XA and XAXa are normal, XaXa are colorblind
- have normal Punnett square except gene decided by the little a or big A on the X
Carrier
person has the gene but isn’t affected (interchangeable for heterozygous)
Pattern of Inheritance
code for what type of trait it is (dominant vs recessive + sex linked vs autosomal)
Autosomal Recessive
- Two unaffected have affected child (always autosomal recessive)
- Two affected have 100% affected kids (always autosomal recessive)
- even distribution between male and female
- trait has possibility of skipping generations
Autosomal Dominant
- Two affected can have unaffected kid (key giveaway)
- Two unaffected have 0% of having affected kid (key giveaway)
- even distribution between male and female generations
- trait doesn’t skip generation
x- linked recessive
- more affected males then females
- affected mom MUST have 100% affected sons
- affected female MUST have affected father
x-linked dominant
- male and female affected equally
- affected female have 50% affected kids
- affected males have 100% affected daughters
If no other patterns match it’s x-linked dominant
(uncommon)
Locus (loci)
physical location of a gene on a chromosome
(larger chromosome = more loci)
Linked Traits
disregard law of independent assortment b/c GENES ON SAME CHROMOSOME
- leads to different phenotypic ratios
* Linked traits have way more offspring with same phenotype as parents*
- crossing over won’t create new genetic combinations if loci are close
Parental vs Recombinant genotypes
Parental Genotype: the genotype of the parents ( in linked traits you see more of them)
Recombinant Genotype: new gene combinations from crossing over (linked genes = less seen genotypes)
Polygenetic Traits
- traits that are controlled by more that one gene ( skin color, eye & hair color, height)
- can’t make a punnett square for these
POLYGENETIC TRAITS = WIDE RANGE OF PHENOTYPES
Dominant Disease
- when the mutation is dominant to the healthy gene
ex Marfan syndrome:
MM = not even born/death
Mm= affected + alive
mm = healthy
*Prescence of one dominant allele = affected
Incomplete Dominance
- when the dominant allele is incompletely dominant over the reccessive
(partially expressed traits) - BLENDED/MIX of traits in the phenotype
ex flower:
R = red, r = white, Rr = pink
a monohybrid cross is the same but the phenotypic ratio would change to 1: 2: 1 bc new phenotype created with heterozygous
Codominance
when 2 or more alleles are equally dominant and equally expressed (neither is recessive)
ex: human blood
A & B are dominant, O is recessive
AA & AO = type a blood
BB & BO = type b blood
AB = type AB blood (codominant)
OO = o blood (recessive trait)
Mitochondrial DNA
- mom (egg) has EVERYTHING (DNA, organelles, cytoplasm that’s why it’s so big, dad only caries 23 chromosomes
- all offspring have 100% mom’s mitochondria (mitochondria make themselves, nucleus doesn’t have code for them)
INHERITANCE OF MITOCHONDREAL DNA IS 100% MATERNAL = affected mom means 100% affected kids
(dad DNA doesn’t matter at all)
- chloroplasts follow same pattern in plants
Environmental effects on Phenotype
changes in the environment lead to changes in the gene expression which changes the organisms’ phenotypes
- Organisms don’t mutate their genes, only expression changes
ex. foxes turn white in winter and red in summer
