Genetics Exam 2

Front 1

Compare & Contrast discontinuous with continuous variation within a population.

Back 1

Discontinuous variation: Phenotypes that fall into two or more distinct, nonoverlapping classes. (controlled by single gene pair; ex. height in pea plants)

Continuous variation: A distribution of phenotypic characters that is distributed from one extreme to another in an overlapping, or continuous fashion. (Controlled by two or more gene pairs; ex. height in tobacco plants, height in humans)

Hint 1

Think numbers of pairs...

Front 2

Compare and contrast single gene inheritance with polygenic inheritance.

Back 2

Some traits are controlled by single genes...mendelian patterns of inheritance.

Polygenic inheritance: controlled by multiple loci, phenotypes are measured in population, phenotypic traits are distributed over a range of the population.

Hint 2

Dont think too abstract.

Front 3

What assumptions must be made to explain the number of phenotypic classes related to the number of genes in simple polygenic inheritance.

Back 3

The different loci are not linked (assorted independently), dominant alleles contribute equally to phenotype. Assume same baseline phenotype, then each dominant allele adds equally to that phenotype, recessive alleles make no contribution to phenotype beyond baseline. Environment acts equally on all genotypes

Front 4

Given certain # of phenotypic classes in simple polygenic inheritance could you determine the number of genes most likely involved...and vice versa

Back 4

2n+1... where n= # of loci.

Hint 4

Equation

Front 5

What happens to the population distribution of phenotypic classes as the number of genes responsible increases?

Back 5

Variation in the population will approach a normal "bell shaped" distribution as the number of loci increases. contolled by two or more genes...few individuals are at the extremes of phenotype, and most individuals are clustered around the average value. Ex. 3 loci = 7 phenotypic classes. 4 loci= 9 phenotypic classes.

Hint 5

Bell

Front 6

What is multifactorial inheritance?

Back 6

*Phenotype is result of multiple loci & environmental interactions

*No direct relationship b/t # of loci and # phenotypic classes

*Most complex human traits are multifactorial

-examples are height, weight, personality, & IQ

Hint 6

Open exposure

Front 7

What is the threshold effect and how does it affect phenotypic variation in multifactorial phenotype? What are the two components of the threshold effect?

Back 7

Explains discontinuous distribution of some complex traits. Liability for a genetic disorder is distributed among individuals in a normal curve. The liability is caused by # of genes, each acting additively. Only individuals who have liability above a certain threshold are affected if exposed to certain environmental conditions. Severity of disease increases as the genetic liability moves away from the mean, and is affected by environmental factors.

*genetic predisposition (liability/susceptability)

*environmental trigger (nongenetic)

Hint 7

Two factors

Front 8

What are the two components of the threshold effect?

Back 8

*Genetic predispostion: individul must inherit minimum # of defective genes (genetic threshold)

*Environmental trigger: at genetic threshold, exposure to proper environmental conditions raise liability of developing disorders.

In other words: environmental conditions are most likely to have the greatest impact on those individuals who have the highest level of genetic predisposition

Hint 8

Nature nuture

Front 9

Compare & Contrast environmental variance with genetic variance...

Back 9

Phenotypic variation is dervied from both sources. (1) different genotypes present in population (2) different environments in which identical phenotypes are expressed.

*Genetic Variance: The phenotypic variance of a trait in a population that is attributed to genotypic differences.

*Environmental Variance: The phenotypic variance of a trait in the population (or individuals with the same genotype) that is attributed to differences in the environment.

Front 10

What is Heritability? How is it interpretted and what are its limitations??

Back 10

Heritability: Expression of how much of the observed variation in a phenotype is due to differences in genotype.

*uses a single # b/t 0 and 1 to express the fraction of phenotypic variation among individuals in a pop. that is due to their genotypes.

Limitations: a calculated H value is only valid for the population being studied under the particular environmental conditions present at the time.

Front 11

H=0

Back 11

100% of the phenotypic variation in the population is due to difference in the environment . Genetics play NO role.

Front 12

H=1

Back 12

100% of the phenotypic variation in population is due to the difference in genotypes of the individual in the population. GENES ARE ENTIRELY RESPONSIBLE FOR CHARATERISTICS

ex. Fingerprints (H almost 1.0)

Front 13

Concordant

Back 13

Agreement between traits exhibited by both twins. Both teins have phenotype

Front 14

Discordant

Back 14

Only one twin has phenotype/exhibits trait

Front 15

Monozygotic Twins (MZ)

Back 15

Twins dervived from single fertilizatio. Involving one egg amd one sperm; such twins are genetically identical

Front 16

Dizygotic Twins (DZ)

Back 16

Twins derived from 2 seperate a d nearly simultaneous ferilizations, each involving 1 egg & 1 sperm. Such twins on average share 50% of their genes

Front 17

What is concordance in MZ twins when phenotype is completely controlled by genetics? Why?

Back 17

100% concordance or H=1

Because MZ twins are genetically identically. Sharing one egg one sperm and same environment

Front 18

What is concordance for DZ twins? Why?

Back 18

H=0.5

50%, Because 2 seperate ova. No more genetically related than siblings

Front 19

Explain genetocs of obesity in both mice & man...

Back 19

Ob gene: leptin hormone fat cells secrete.

Db gene: leptin receptor in hypothalamus

*mutation in either ob or bd resulted in fat mice.

In twin studies: H= range from 0.3-0.7 twin concordance

*human ob & db genes are mutated in only 5% of obese individuals studied. Environment/activity has more of an effect on human obsesity that in mice.

Front 20

Chromosome #'s

Back 20

Autosomes 1-22

Sex chromosome X&Y

24 chromosomes in humans

Front 21

Chromosome arm designation

Back 21

P arm: short, smaller arm

Q arm: long, bigger arm

Front 22

Chromosome region number correlation

Back 22

# from centromere outward

Front 23

Band #

Back 23

Treat with banding techniques

Get exactly same banding patterns consistent from person to person.

Unique to chromosome #.

Allows geneticists to refer to a particular region on chromosome.

Front 24

Metacentric

Back 24

Almost equal arm lengths

Front 25

Submetacentric

Back 25

Clearly unequal arm lengths

Front 26

Acrocentric

Back 26

P arms are very small

Front 27

Telacentric

Back 27

Looks like no arms, but arms are present..just so small almost not visiable

Front 28

What is a karotype?

Back 28

Picture of the 22 chromosome + sex chromosomes. Organized and numbered...mapped out neatly

Front 29

How is a karotype done?

Back 29

Mitogens are used to stimulate cell division. Arrest cells in metaphase with colcemid. Spindle appartus is inhibited. Chromosomeds spread...cuz cells are treated to break open.

*specimins that can be uses are

-leukocytes

-fibroblasts

-amniotic cells (amniotic fluid)

- chorionic cell (placenta)

Front 30

What is chromosome banding?

Back 30

Reproducible and chromosome specific patterns of light & dark areas

Produced by chemical or heat treatment of chromosomes on slides.

Every chromosome has unique banding pattern.

Front 31

G bands

Back 31

*most common used

Stains with Giemsa to produce dark & light bands. Chemical digests proteins.

Dark bands= G bands

Front 32

R bands

Back 32

Same treatment as G bands, but stain with quinacrine mustard to make flourese under UV light

Front 33

C bands

Back 33

Chemicals digest DNA, stain w/ Giemsa

* only centromeres show dark bands, hence C bands

Front 34

Chromosome Painting

Back 34

Chromosome specific probes have been designed. These probes only react with a particular chromosome.

*dye to particilar chromosome. Differeny color shades

**look at interphase on living cells

Chrimosome territories allowed them to follow colors

Front 35

Compare & Contrast Amniocentesis with Chorionic Villi Sampling (CVS)

Back 35

Amniocentesis: *aniotic fluid done at 16 weeks

* needle into sac around baby. Risk of complications. Week to get results back. Invasive and can hurt baby if not done properly.

CVS: *sample placental tissues, lots of cells

* similar risks as amnio

*8 weeks gestation, several days to get results

Non-invasive and quicker results

Front 36

Polyploidy

Back 36

Abnormality based on #

Chromosome number is a multiple of haploid set -multiple of 23(humans)

Common in plants

Front 37

Triploidy

Back 37

Three haploid sets

(Human= 3x23=69)

15-18% spontaneous aborted fetuses

75% of the extra chromosomes are paternal. Dispermy..2 sperm fertilize same ova

Front 38

Tetraploidy

Back 38

Four haploid sets

(4x23=92)

5% spontaneous aborted fetuses

Due to first cleavage division failure

Front 39

Aneuploidy

Back 39

Abnormality of chromosome number that is not polyploidy (DOES NOT INVOLVE COMPLETE HAPLOID SET)

Due to nondisjunction (chromosome did not seperate as supossed to)

-homologous pair in meiosis I

- sister chromatids in meoisis II

- sister chromatids in mitosis cleavage divisions

*Chimera (some cells normal, one will be missing 21, one will have extra 21

Front 40

Compare/Contrast type of gametes in meiosis 1 vs meiosis 2

Back 40

In meiosis , 2 xtra chromosome, 2 missing.(4 total gameyes)

In meiosis 2 , 1 xtra, 1 missing(4 total gametes)

Front 41

Automsomal vs. Sex chromosone monosomy

Back 41

Autosomal : 1 chromosome is missing human 45..lethal no live births

Sex: can survive if have x and missing 2nd...x0 turners syndrome

Front 42

Trisomy 13

Back 42

Patau Syndrome. Xtra 13..cns 💖 malformations severe congenial malformations

Front 43

Trisomy 18

Back 43

Edwards- xtra 18 similiar malformations as 13. More females affected

Front 44

Trisomy 21

Back 44

Down Syndrome. Xtra 21 mental retardation. Protruding tongue, heart defects

Front 45

Sex chromosome aneuploidy

Back 45

Turners(XO) monosomy. normal iq, slightly abnormal appearance.

Klinefelter's (XXY) trisomy tall stature, 60% due to maternal nondisjunction. Additonal Xs

XYY- impulse control...normal appearence. Normal fertility tall. Slightly lower iq

Front 46

Inversion

Back 46

Part of chromosome is rearranged now inverted.

Front 47

Translocation

Back 47

1 part of chromsome is transferred to another.

Front 48

Reciprocal translocation

Back 48

No gain or loss of genetic material. Balanced exvhange.

Gametes may be unbalanced

May lead to monosomy or trisomy

Front 49

Robertsomian translocation

Back 49

Exchange is not balanced. Some material lost.

Front 50

Inherited form of down syndrome

Back 50

T14/21 balanced translocation. Carrier is phrnitypicall normal but unbalanced gametes, may lead to down's in offspring

Front 51

Pericentric vs paracentric inversions

Back 51

Peri- include centromere breakpoint in each arm

Para- not include centromere n both breaks occur in one arm on chromisome

Front 52

Hardy-weinberg

Back 52

P= frequency dominant alleles

Q= frequency recessive allles

P2 + 2pq + q2 = 1