chapter 7 complex traits

from in class powerpoint 3/3/25 and 3/5/25

empiric risks

concept used in genetics and
medicine to estimate the probability that a certain
trait or condition will occur again in a family.

Incidence

measures how often new cases occur over
time

Prevalence

shows how common a condition is at a
particular point in time.

heritability

a measure used in genetics to describe how
much of the variation in a particular trait within a population
can be attributed to genetic differences among individuals

heritability can be population specific? t or f

t; Heritability can vary between
populations and environments. For example, the
heritability of a trait in one country might be
different from its heritability in another country due
to different environmental influences.

describe heritability estimate

Heritability is expressed as a
percentage or a value between 0 and 1.
• A heritability of 0 means that genetics do not
contribute to the variation in the trait at all,
• A heritability of 1 means that genetics are the only
reason for the variation.
• Most traits fall somewhere in between

define concordance

measures the frequency of expression of a
trait in both members of monozygotic (MZ) or dizygotic
(DZ) twins

describe relation between dizygotic, monozygotic, twins raised apart, and adopted individuals

Dizygotic twins = Shared
environment and 50% of genes
Monozygotic twins = Identical
genotype and shared environment
Twins raised apart = Shared
genotype but not environment
Adopted individuals = Shared
environment but not genes

what is a copy number variant? (CNV)

insertions of short DNA repeats

whats the purpose of a GWAS ( genome wide association study)?

seek SNPs
that are shared with much greater frequency among
individuals with the same trait than among others
Figure 7.10

polygenic risks scores

can be used to predict illness, calculated from the number of risk alleles weighted by effect sizes, calculated form the GWAS data.

what the hell is a cohort study?

Researchers follow a large group of individuals
over time and measure many aspects of their health.
• The most famous is the Framingham Heart Study

what is the case control study?

People in two groups are individually
matched for several characteristics, and
differences in SNP patterns are identified

homozygosity mapping?

Disease-causing mutations are identified in
homozygous genome regions that children
inherit from parents who are related to
each other.

P arm

The short arm of a chromosome, located above the centromere.

Q arm

The long arm of a chromosome, located below the centromere.

Telomeres

Repetitive DNA sequences at chromosome ends that protect against degradation.

Heterochromatin

Tightly packed, transcriptionally inactive DNA, often found near centromeres and telomeres.

LOOKS DARK

Centromere

The constricted region where sister chromatids attach; essential for chromosome segregation.

Euchromatin

Loosely packed, transcriptionally active DNA involved in gene expression.

LOOKS LIGHT

Sister chromatids

Identical copies of a chromosome, connected at the centromere, formed during DNA replication.

Karyotypes

display the
chromosome pairs from
largest to smallest

Chromosome Centromere Positions
• Telocentric

at the tip

Chromosome Centromere Positions
• acrocentric

close to the center

Chromosome Centromere Positions
• submetacentric

off center

Chromosome Centromere Positions
• metacentric

at center

chromosome deletion examples, what causes prader willi syndrome? (PWS)

lack of active genetic material in a specific region of chromosome 15 (15q11-q13), most commonly due to a deletion of the paternal (FATHERS) copy of this region

what is the fish technique for chromosomes

Fluorescence in situ hybridization - a cytogenetic technique that uses fluorescently labeled DNA probes to detect and locate specific DNA sequences on chromosomes, aiding in the diagnosis and identification of genetic abnormalities

given the abbreviation, give the description 46,XY

Chromosomal male

given the abbreviation, give the description 46,XX

Back: Chromosomal female

given the abbreviation, give the description

45,X

A female with one X

given the abbreviation, give the description 47,XXY

A male with an extra X

given the abbreviation, give the description

47,XYY

A male with an extra Y

given the abbreviation, give the description

46,XY,del(7q)

A male missing part of the long arm of chromosome 7

given the abbreviation, give the description

47,XX,+21

A female with trisomy 21 (Down syndrome)

given the abbreviation, give the description

46,XY,t(7;9)(p21.1;q34.1)

A male with a translocation between the short arm of chromosome 7 at band 21.1 and the long arm of chromosome 9 at band 34.1

given the abbreviation, give the description

48,XXYY

A male with an extra X and an extra Y chromosome

Graphical
representations called
_________depict the
arms (p or q), bands,
and subbands of
chromosomes

ideograms

Front: Polyploidy

Back: Extra chromosome sets

Front: Aneuploidy

Back: An extra or missing chromosome

Front: Monosomy

Back: One chromosome absent

Front: Trisomy

Back: One chromosome extra

Front: Deletion

Back: Part of a chromosome missing

Front: Duplication

Back: Part of a chromosome present twice

Front: Translocation

Back: Two chromosomes join long arms or exchange parts

Front: Inversion

Back: Segment of chromosome reversed

Front: Isochromosome

Back: A chromosome with identical arms

Front: Ring chromosome

Back: A chromosome that forms a ring due to deletions in telomeres, which cause ends to adhere

Front: Chromothripsis

vBack: One or more chromosomes shatters

euploid

normal chromosome number

turner (XO) syndrome

about 1/2500 female births, 99% die in utero

Features;

short stature, webbing at the back of neck, incomplete sexual devleopment (infertile)

impaired hearing

triplo - x syndrome

about 1 in every 1000 female births

effects

tallness, enstrual irregularities, and slight impact on intelligence

lack of symptoms reflects X - INACTIVATION

klinefelter (XXY) syndrome

about 1 in 500 male births

features include

incomplete sexual development

rudimentary testes and prostate

long limbs, large hands and feet

some breast tissue development

what does balanced mean in atypical chromosomes?

they have the normal amount of genetic material

what does unbalanced mean in atypical chromosomes

they have extra or missing DNA sequences

what is comparative genomic hybridization (CGH)

used to detect very small CNVs; microdeletions, and microduplications,

used to help diagnose autism, intellectual disability, learning disabilities, other behavioral conditions