Genetics 380 Exam 1 Review Sheet | Study notes Genetics

Exam 1 Master Sheet

Lecture 1

Pre-Mendel: sperm and egg contain essences that mix upon conception(pangenesis) to form a new pattern

Peas as model organism: cheap, easy to grow, self-fertilizing, can be cross pollinated

Mendel’s Success: used true-breeding strains, used contrasting characteristics, quantified his results

Conclusions: male and female parents contribute equally(reciprocal crosses gave same results) (no blending)

Dominant vs. Recessive Traits - dominant displayed in F1, recessive trait only in F2

Particulate inheritance - traits are determined by discrete units inherited thru generations - 2 particles in genotype,

but only one is passed on

Steps for Determining results of a hybrid cross.

1. Determine gametes for parents

2. Write gametes and frequency along the side of the table

3. Combine gametes + translate genotype into phenotype

Mendel’s First Law: Principle of Segregation - members of a pair of allele segregate into separate gametes

Gametes form in equal frequencies - homozygote makes 1 type, heterozygote makes two. Subsequent fertilization

is random. Phenotype does not always reveal genotype - Dominant Phenotype can be homo-or heterozygous

Testcross/backcross to determine genotype - cross individual with dominant phenotype to homozygous recessive

Lecture 2 Mitosis and Meiosis

Chromosome - physical structure that carries genes - double-stranded DNA, information arranged linearly

Eukaryotes: contains DNA, RNA and proteins. Dispersed/chromatin for most of the cell cycle - bundles in division

Eukaryotic chromosomes have a distinct shape and size, 1 centromere and 2 telomeres

Distinguished by size and location of centromere relative to telomeres (acro, meta, submeta, telo - centric)

Chromosome # per cell differs among species, but most eukaryotes have 2 copies per somatic cell (2N/diploid #)

2 copies of each chromosome in a diploid = homologous (same length, same centromere, same gene placement)

Must be copied and separated equally during each stage of division

Mitosis: 1 cell -> 2 cells that are genetically identical. Creates somatic cells

Meiosis 1 cell -> 4 variable daughter cells. ½ number of chromosomes in somatic cells. Creates gametes

The Cell Cycle - stages that 1 cell goes through as it grows and divides

G0 - non-dividing phase - cell is stable and at constant size

G1 - 1st gap or growth phase - proteins needed for cell division are synthesized

S - Synthesis - all chromosomes are duplicated

G2 - 2nd gap or growth phase - damaged DNA must be repaired

Mitosis - cell division

Phases of Mitosis:

Prophase: chromosomes condense, mitotic spindles form, nuclear envelope breaks down

Metaphase: microtubules from spindle pole attach to each chromosome at the centromere

- chromosomes moved to metaphase plate in the center of the cell

Anaphase - proteins holding sister chromatid centromeres together are degraded, sister chromatids disjoin

- Sister chromatids move to opposite spindle poles’

Telophase: nuclear envelope reforms across each daughter nucleus, chromosomes uncoil, spindle disappears

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Exam 1 Master Sheet

Lecture 1

Pre-Mendel: sperm and egg contain essences that mix upon conception(pangenesis) to form a new pattern Peas as model organism: cheap, easy to grow, self-fertilizing, can be cross pollinated Mendel’s Success: used true-breeding strains, used contrasting characteristics, quantified his results Conclusions: male and female parents contribute equally(reciprocal crosses gave same results) (no blending) Dominant vs. Recessive Traits - dominant displayed in F1, recessive trait only in F Particulate inheritance - traits are determined by discrete units inherited thru generations - 2 particles in genotype, but only one is passed on Steps for Determining results of a hybrid cross.

Determine gametes for parents
Write gametes and frequency along the side of the table
Combine gametes + translate genotype into phenotype Mendel’s First Law: Principle of Segregation - members of a pair of allele segregate into separate gametes Gametes form in equal frequencies - homozygote makes 1 type, heterozygote makes two. Subsequent fertilization is random. Phenotype does not always reveal genotype - Dominant Phenotype can be homo-or heterozygous Testcross/backcross to determine genotype - cross individual with dominant phenotype to homozygous recessive

Lecture 2 Mitosis and Meiosis

Chromosome - physical structure that carries genes - double-stranded DNA, information arranged linearly Eukaryotes: contains DNA, RNA and proteins. Dispersed/chromatin for most of the cell cycle - bundles in division Eukaryotic chromosomes have a distinct shape and size, 1 centromere and 2 telomeres Distinguished by size and location of centromere relative to telomeres (acro, meta, submeta, telo - centric) Chromosome # per cell differs among species, but most eukaryotes have 2 copies per somatic cell (2N/diploid #) 2 copies of each chromosome in a diploid = homologous (same length, same centromere, same gene placement) Must be copied and separated equally during each stage of division Mitosis : 1 cell -> 2 cells that are genetically identical. Creates somatic cells Meiosis 1 cell -> 4 variable daughter cells. ½ number of chromosomes in somatic cells. Creates gametes The Cell Cycle - stages that 1 cell goes through as it grows and divides G 0 - non-dividing phase - cell is stable and at constant size G 1 - 1st gap or growth phase - proteins needed for cell division are synthesized S - Synthesis - all chromosomes are duplicated G 2 - 2nd gap or growth phase - damaged DNA must be repaired Mitosis - cell division Phases of Mitosis : Prophase: chromosomes condense, mitotic spindles form, nuclear envelope breaks down Metaphase: microtubules from spindle pole attach to each chromosome at the centromere

chromosomes moved to metaphase plate in the center of the cell Anaphase - proteins holding sister chromatid centromeres together are degraded, sister chromatids disjoin
Sister chromatids move to opposite spindle poles’ Telophase: nuclear envelope reforms across each daughter nucleus, chromosomes uncoil, spindle disappears

Meiosis : gamete formation. 4 haploids from 1 diploid cell. 2 divisions (meiosis 1 and 2, reduction and equational) Cell goes through s phase before meiosis Phases of Meiosis Early Prophase 1: chromosomes condense, homologs pair/synapse, crossing over may happen at chiasmata, 5 Stages of Propahse 1: describe appearance of chromosomes as they condense, pair and recombine

Leptotene “thin thread” condensation begins
Zygotene - “paired thread” synapsis begins
Pachytene - “thick thread” condensation continues, recombination,
Diplotene - “double thread” synapsis breaks down, chiasmata keep homologs joined
Diakinesis “moving apart” DNA synthesis happens during homologous recombination - crossing over between homolgous chromosomes One sister chromatid from each homolog participates in a single crossover event Late Prophase 1: chromosomes condense, homologs pair, crossing over(or not), spindle, envelope breakdown Metaphase 1: each pair of homologs takes up a position on the metaphase plate (homologous pairs align) Anaphase 1: members of homologous pairs disjoin and move to opposite poles (principle of segregation) Telophase 1 - nuclear envelope reforms, interkinesis happens, producing 2 haploid (½ number of chromosomes) Prophase 2 - chromosomes condense, spindle forms, nuclear envelope breaks down Metaphase 2 - individual chromosomes position in equatorial plate Anaphase 2 - sister chromatids are pulled to opposite poles - chromosome count in cell doubled Telophase 2 - nuclear envelope reforms, cytokinesis happens Lecture 5 - Non-Mendelian Ratioes Conditions for Mendel’s Experiments
All traits being considered are unlinked, each gene assorts independently, each gene codes for 1 trait
Every gene has 2 alleles that specify a unique phenotype - 1 allele is dominant over the other
Genotype determines phenotype Mendelian Ratios: Monohybrid Cross 3:1 Dihybrid Cross 9:3:3:1 - why can expression differ from these ratios? Causes involving a single locus: - different types of dominance, multiple alleles, lethal alleles Causes involving multiple loci - incomplete penetrance, variable expressivity Complete dominance - phenotype of heterozygote is phenotype of a homozygote (3:1, 9:3:3:1) Incomplete dominance - intermediate phenotype in heterozygote RR(red), Rr(pink), rr(white) (1:2:1) Codominance - heterozygote has phenotypes of both homozygotes (blood types A, B, AB) Multiple alleles - any individual only carries 2 alleles - may form a dominance series Lethal Alleles - found in essential genes, dominant/recessive, Dominant trait displayed in heterozygote (homozygote does not survive development) (2:1) Penetrance - proportion of individuals w a particular phenotype displaying the expected phenotype

Incomplete - less than 100% of population displays the trait (give appearance of skipping generations, may preserve lethal alleles, varying genetic backgrounds Expressivity - phenotype varies among individuals with the same genotype (variation in severity), varying genetic backgrounds and environmental effects. Polydactly is an example of incomplete penetrance and variable expressivity.

Lecture 4 - Sex Influence and Pedigrees

Studying heredity in humans is challenging:

Can’t test in humans through a cross, difficult to determine mendelian ratios
Deduce modes of inheritance in a trait using pedigrees to visualize how the trait is expressed in families Typically making a best guess - selecting the mode that makes the most sense based on available data Dominant vs/recessive - complete dominance, 1 parent always displays shows phenotype Autosomal vs sex-linked? - both sexes are affected equally if autosomal Do not assume individuals marrying into the family are carries Points to keep in mind
Incomplete penetrance and variable expressivity can make a dominant trait appear to skip generations Incomplete penetrance(disease allele is present but is not expressed) Variable Expressivity(disease allele is expressed differently) Sex influenced and sex-limited traits can be passed down by an unaffected individual
always autosomal, expression dependent on sex of carrier Geneticists typically look at many families and multiple generations to understand the mode of inheritance Sex influences on heredity: Sex-linked trait - genes on the sex chromosome. Sex influenced - autosomal, but expressed more in 1 sex. Sex limited - autosomal gene limited to the expression of one sex. Genetic maternal effect - nuclear genotype of the maternal parent. Cytoplasmic genes - inherited from 1 parent Genomic imprinting - genes whose expression is affected by the sex of the parent Genetic maternal effect - genotype inherited from both parents, but phenotype reflects mother’s genotype Cytoplasmic Inheritance - genes in chloroplasts and mitochondria
mitochondria express different phenotypes when segregated during cell division
Mother to offspring b/c egg contributes the majority of the cytoplasm
Reciprocal crosses give different results and extensive phenotypic variation Genomic Imprinting - whether inherited from mom or dad. Different results for reciprocal crosses, epigenetics

Lecture 6 - Non - Mendelian Ratios Causes involving multiple loci/environment - environmental modification/gene interaction Causes involving sex-determination - sex linkage, sex limited traits, sex influenced traits Environmental modification - genotype alone does not determine phenotype, environmental conditions can affect it

Himalayan rabbits(variable based on body temperature) and freckles(exposure to sunlight) Gene interaction: genes at 2+ loci influence a trait - non allelic, can lead to…. (Deviation from 9:3:3:1)
New and unexpected phenotypes from crosses (pea, walnut, rose, and single phenotypes in chicken combs)
Epistasis(alleles at 1 locus mask expression at another locus) - eye color in fruit flies
complementation (crossing 2 recessive mutants yields wild-type progeny).complementation test (mutant cross) Identifying gene interaction: ratio is a variation of 9:3:3:1, a single trait is influenced by more than 1 gene Sex chromosomes are differently shaped/heteromorphic - act homologous in meiosis due to pseudoautosomal regions X-linked, Y linked, Z linked, W Linked Humans - XX/XY - Y confirms maleness (sry - sex determining region on the Y) - males heterogametic ZZ/ZW - females are heterogametic - reciprocal crosses give different results In fruit flies, the ratio of X-chromosomes to autosomes gives the sex. x<0.5=metamale, .5=male, .5-1 intersex, 1 = female, x>1 = metafemale. (y chromosome required for fertility) T.H. Morgan and Fruit Fly Eyes - initially thought white eyes in female are lethal…. White eyed females viable… reciprocal cross not the same… sex linked. Dosage compensation corrects for potential imbalance in X-linked gene products in females vs males Females have 2 copies - homozygous or heterozygous. Males are hemizygous - traits are always expressed X-inactivation - random, early in development - all daughter cells have the same x inactivated (mosaicism) (Barr body) Sex-influenced - more common in 1 sex. autosomal, male/female affects dominant/recessive (goatbeard) Sex limited - autosomal, zero penetrance in 1 sex - related to secondary sex characteristics Lecture 7 - Gene Linkage in Eukaryotes 23 chromosomes, 20,000 genes. Can’t all assort independently - genes that don’t assort independently = linked. Linkage - deviation from independent assortment favoring parental gametes vs recombinant(not possible in parents) Physical linkage - proximity to each other on chromosome, measured in base pairs/bp Statistical linkage - how physical linkage is observed, experimental data, map units/centimorgans Complete linkage - so close that they never assort independently Testcross in linkage - homozygous recessive crossed to individual with known genotype to show if gametes show deviation from independent assortment Complete Linkage (f(recomb) = 0). Independent Assortment = f(parent) = f(recomb) Incomplete linkage = f(parental) > f(recomb) > 0. Crossing over - physical exchange of chromosomal material between 2 homolgous chromosomes Recombination between 2 genes on homologous chromosomes at 2 different loci (1mu - 1%RF = 1centimorgan) Distance between genes based on detecting linkage and estimating recombination frequency Can also show order of genes based on triple testcross experiment - recombination among 3 genes, 2 single crossovers and a double crossover

Genetics 380 Exam 1 Review Sheet, Study notes of Genetics

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Download Genetics 380 Exam 1 Review Sheet and more Study notes Genetics in PDF only on Docsity!

Exam 1 Master Sheet

Lecture 1

Lecture 2 Mitosis and Meiosis

Lecture 4 - Sex Influence and Pedigrees