Genetics Chapter 6: Pedigree Analysis, Applications, and Genetic Testing

controlled matings are not possible, long generation times, family size is small

what are the major challenges in studying human genetics?

a pictorial representation of a family history that outlines the inheritance of one or more characteristics

what is a pedigree?

helps them study inheritance patterns for characteristics or genetic diseases

how do geneticists use pedigrees?

squares

what are males represented by in a pedigree?

circles

what are females represented by in a pedigree?

diamond

what are nonbinary or gender fluid individuals represented by in a pedigree?

a mating

what does a horizontal line drawn between two symbols in a pedigree indicate?

an autosomal dominant type of deafness, accompanied by fair skin, a white forelock, and visual problems

what is Waardenburg syndrome?

the person exhibits the trait

what do filled symbols in a pedigree mean?

the person from whom the pedigree is initiated (first affected family member)

what is the proband?

a roman numeral

how is a generation defined in a pedigree?

listed in birth order from left to right

how are children listed in a pedigree?

clear Mendelian ratios are usually impossible to discern in a single pedigree

what does a limited number of offspring in human families mean?

penetrance, sex-influenced traits, and other extensions of Mendelian Principles

what traits add to challenges with human genetics?

with equal frequencies in both sexes, tends to skip generations

how do autosomal recessive traits appear in pedigrees?

affected, unaffected

in autosomal recessive traits, ___ offspring are usually born to ___ parents

1/4

in an autosomal recessive trait, when both parents are heterozygous, approximately how many offspring will be affected?

mating between closely related people

what is consanguinity?

consanguineous

autosomal recessive traits appear more frequently among the children of ___ marriages

both sexes with equal frequency, both sexes transmit, does not skip generations

how do autosomal dominant traits appear in a pedigree?

an affected parent (unless they possess a new mutation)

offspring affected with an autosomal dominant trait must have...

half

in autosomal dominant traits, when one parent is a heterozygote and the other is unaffected, approximately how many offspring will be affected?

no

do unaffected parents transmit autosomal dominant traits?

Tay-Sachs

what is an example of an autosomal recessive trait?

children appear healthy at birth but become weak around 6 months old, gradually conditions worsen, often die at 2-3 years old

describe Tay-Sachs disease

accumulation of a lipid called CM2 ganglioside in the brain, lack enzyme called hexosaminidase

what is Tay-Sachs caused by?

heterozygous

if an autosomal dominant allele is rare, most people displaying the trait are ___

3/4

if both parents are heterozygous for an autosomal dominant trait, how many of their children will be affected?

familial hypercholesterolemia

what is an example of an autosomal dominant trait?

males

who is usually more affected by X-linked recessive traits?

often skip generations

how do X-linked recessive traits appear in a pedigree?

about half

how many sons are affected by an X-linked recessive trait if their mother is a carrier?

no, never

are X-linked recessive traits passed from father to son?

all are carriers

if a father is affected by an x-linked recessive trait, what is true about his daughters?

individuals whose heterozygous genotype can be definitively determined from a pedigree

what are obligate carriers?

hemophilia A

what is an example of an X-linked recessive trait?

faulty or missing factor VIII, a protein in the clotting cascade (gene is located on tip of X chromosome)

what causes hemophilia A?

both are affected, oftentimes more females than males

how do X-linked dominant traits affect males vs females?

do not skip a generation

how do X-linked dominant traits appear on a pedigree?

he passes the trait to all of his daughters

what is true about a father affected by an X-linked dominant trait?

half her sons and half her daughters

if a mother is heterozygous for an X-linked dominant trait, how many of her children will be affected?

hypophosphatemia

what is an example of an X-linked dominant trait?

only males are affected, passed from a father to all of his sons, does not skip generations

how do y-linked traits appear on a pedigree?

condition in which regions of tissue within a single individual have different chromosome constitutions

what is genetic mosaicism?

genes, environment, or a combination of the two

what can traits in twins be the result of?

nonidentical (fraternal), arise when two separate eggs are fertilized by two different sperm, producing genetically distinct zygotes

what are dizygotic twins?

identical, result when a single egg, fertilized by a single sperm, splits early in development into two separate embryos

what are monozygotic twins?

help us understand the influence of genetic and environmental factors

what is the purpose of comparing dizygotic and monozygotic twin pairs?

both members of a twin pair have a trait

what does it mean if twins are concordant?

only one member of the pair has the trait

what does it mean if twins are discordant?

the percentage of twin pairs that are concordant for a trait

what is concordance?

50%

what percentage of genes do dizygotic twins share?

100%

what percentage of genes do monozygotic twins share?

higher in monozygotic twins

what is true about concordance of genetically influenced traits?

death from acute infection

what is an example of a trait that is less influenced by genetics?

asthma

what is an example of a genetically influenced trait?

examine the effects of environment on characteristics

what does adoption allow geneticists to do?

the characteristic is attributed to environmental factors

what does it mean if adoptees and their parents show similarities in a characteristic?

BMI, at least partially influenced by genetics

what is an example of a characteristic tested by adoption? is the trait genetic or environmental?

a field that provides information to patients with genetic conditions and others who are concerned about hereditary conditions

what is genetic counseling?

a diagnosis of a condition that may have a genetic basis

what does genetic counseling usually begin with?

to recognize the potential for a genetic condition at an early stage

what is the ultimate goal of genetic testing?

testing that can recognize genetic conditions at an early stage to help make informed decisions about reproduction

what is genetic testing?

those that are conducted before birth

what are prenatal genetic tests?

procedure for visualizing a fetus, detecting conditions like cleft lip or palate

what is ultrasonography?

prenatal testing of fetal tissue that involves obtaining a sample of amniotic fluid from the uterus of a pregnant woman

what is amniocentesis?

procedure that can be performed earlier in pregnancy, collects a larger amount of fetal tissue for testing

what is chorionic villus sampling?

the complete set of chromosomes possessed by an organism, usually presented as a picture of a complete set of its metaphase chromosomes

what is a karyotype?

to produce a karyotype

what can harvested fetal cells be used for?

abnormalities (aneuploidy) or normal sets of chromosomes (euploid)

what can karyotypes show?

method of screening for genetic conditions in a fetus by examining levels of certain substances in the blood of the mother

what are maternal blood screening tests?

alpha-fetoprotein, indicates neural-tube defects

what is an example of something tested in maternal blood screening?

genetically testing of fetus performed by testing fetal DNA found within the maternal blood

what is noninvasive prenatal screening?

genetic testing on an embryo implanted via in vitro fertilization, free of specific genetic defect

what is preimplantation genetic diagnosis?

testing for genetic disorders in newborn infants, early identification of testing conditions can lead to effective treatment

what is newborn screening?

testing of healthy adults for genes that might predispose them to a genetic condition in the future

what is presymptomatic genetic testing?

testing to identify heterozygous carriers of a disease-causing allele who have the potential to produce children who have the disease

what is heterozygote screening?

testing to determine the effectiveness of a treatment on an individual

what is pharmacogenetic testing?

genetic information nondiscrimination act, prohibits health insurance discrimination based on genetic information

what is GINA?

covers- health insurance and employment

doesn't- life, disability, and long-term care insurance

what does GINA cover? What does it not?