UNIT 1: Genetics

Below you will find some text I created that is consistent with the notebooks you received in class. These notes are not as up to date as the ones you get in class but can be a good reference if you missed a class or need a slightly different explanation. Also, there are occasionally links to external resources throughout the site below.

UNIT 1: Principles of Inheritance

• Every living organism is made up of many different traits, or distinguishing characteristics, that make it unique (ex: eye colour, hair colour)
  • Traits may be obvious and visible like the colour of hair, or very subtle like different types of proteins on the outside of a cell.
  • The difference in traits is how we separate individuals from each other, and even different species from one another.
• Transmission of traits from one generation to the next is called heredity.
  • Heredity is why one generation is similar to the next.
    • Traits that seem to be the same between generations of organisms are said to be "inherited"
  • BUT for most organisms each generation is only similar not identical to the last.
    • This is known as variation.

Genetics

• Deals with the principles of variation and inheritance in animals and plants.
• It is the science that looks for patterns and explanations for why some traits seem to be inherited and others are not.

As early as 960CE there are records of scientists having theories and understanding of genetics. The Islamic scientist and medical practitioner Abu al-Qasim al-Zahrawi's writings showed his clear understanding of the inheritance patterns of hemophilia, in addition to his important contributions to medicine.

Gregor Mendel is an example of a European scientist who's research into genetics is well known and studied.

• Born in 1822
• Attended the University of Vienna
• Studied chemistry, biology, and physics
• Austrian monk and a plant breeder
• Began investigations of the inheritance of certain traits in pea plants (Pisum Sativum)

Why did he study Pea Plants?

• Studied a lot of different plants, but pea plants gave the most consistent results and they:
  • Grow and reproduce quickly
  • Mating can be controlled
  • Have distinct traits that are readily (easily) observed (7 traits)

Traits

• Each trait has only 2 possible forms or variations.
  • Yellow or green
  • Smooth or wrinkled
  • Tall or short
  • Purple flower or white flower
  • Etc.

Mendel’s Experiments

• To understand how traits are inherited, he cross pollinated them
  • Transferred male gametes from the flower of a green pea plant to the female organ of a yellow pea plant
  • These plants are called the P (parent) generation
• The P generation produced plants with only yellow peas
  • The offspring of the P cross is called the first filial generation (F₁ Generation)
• Was the green pea trait hidden or no longer present?
  • To find out, Mendel allowed the F₁ generation to self – fertilize
• The offspring from the F₁ generation are the second filial generation (F₂)
  • 75% produced yellow peas
  • 25% produced green peas

Mendel’s Conclusion

• There must be 2 forms of the seed trait in pea plants – yellow peas and green peas
  • Each is controlled by a factor (allele)
  • Allele: alternative form of a single gene passed from generation to generation

Alleles

• Dominant alleles: represent a characteristic always expressed (appears) in an individual.
  • Yellow pea plant
• Recessive allele: represents a characteristic usually not expressed; it is masked by the dominant trait
  • Green pea plant

Gametes, sexual reproduction, and Mendellian genetics

• In sexual reproduction two gametes are formed by (typically) two separate individuals and combined to form a zygote, that grows into a new individual.
• Each gamete has only one allele for each of the traits necessary to create a viable organism (since each individual has two alleles for each of their traits).
• This means that each of the parent individuals contributes half the information necessary to creating the zygote.
• Some rules apply to the formation of these gametes and zygote in order for the inheretance observed to be considered "Mendellian" (the type of inheritance that follows mendels observations).

Mendel’s Laws or Principles or Inheritance

• The Principle of Genes in Pairs
• The Principle of Dominance and Recessiveness
• The Principle of Segregation
• The Principle of Independent Assortment

Principle of Genes in Pairs

• Genetic characteristics are controlled by genes that exist in pairs (alleles) passed from parent to offspring.
• Each parent gives their offspring one allele from each pair.
• One allele is dominant and other is recessive
• Example:
  • Gene for pea color expressed two ways: green or yellow
  • Yellow pea color is dominant over green pea color
  • Two alleles for pea colour : Y and y
    • Y = Yellow
    • y = Green

Principle of Dominance and Recessiveness

• Allele: alternate form of gene
  • Example: the gene for flower color has an allele for purple flowers and an allele for the white flowers
  • If the two alleles at a locus (spot on a chromosome) differ, then the dominant allele determines the organism’s appearance, and the recessive allele has no noticeable effect on appearance

• Alleles T and t
  • T = dominant (upper – case)
  • t = recessive (lower – case)
    • TT = homozygous dominant (purebred)
    • tt = homozygous recessive (purebred)
    • Tt = heterozygous (hybrid)

*Homozygous: the two alleles for a gene are the same

*Heterozygous: the two alleles for a gene are different

• Carriers (Tt)
  • Heterozygous individuals
  • Carry the recessive allele but do not show the recessive trait (show dominant)
  • Can pass recessive allele on to offspring

Genotype and Phenotype

• Because of dominant and recessive alleles, an organism’s traits do not always reveal its genetic composition
• Phenotype: physical appearance (purple flower, tall plant, etc.)
• Genotype: genetic makeup (PP, Pp, pp, etc.)
• Example: If P represents the dominant allele for purple flowers and p represents the recessive allele for white flowers:
  • Genotype = PP; Phenotype = purple flowers
  • Genotype = Pp; Phenotype = purple flowers
  • Genotype = pp; Phenotype = white flowers

Principle of Independent Assortment

• Alleles for a trait separate randomly when gametes are formed
• Each gamete has an equal chance to gain either allele for each of its traits.
• i.e. there is no guarantee that if a gamete has a brown allele for hair colour it also has the brown allele for eye colour (we'll soon learn that this principle is not entirely true)

Principle of Segregation

• The two alleles for a heritable trait separate (segregate) during meiosis and end up in different gametes
• Thus, a gamete gets only one of the two alleles

Summary

• Gregor Mendel discovered inheritance through this experiments with pea plants.
• Dominant and recessive traits.
• Homozygous and heterozygous individuals.
• Genotype and phenotype.

Punnett Square

• Used to calculate the probability of inheriting a particular trait.
• Illustrates all possible combinations of gametes from a given set of parents.
• Gametes for one parent is listed across the top.
• Gametes for another parent is listed down the side.
• Each box is filled by copying the row and column – head letters across or down the empty squares.
• This will give you a prediction of the outcome of a particular cross for a given set of alleles
  • Genotype: genetic make – up of an organism
  • Phenotype: appearance of the trait in an organism
• Example: Gg × Gg
  • Alleles: G = green; g = yellow

Monohybrid Cross

• Mono’ = 1; ‘Hybrid’ = heterozygous
• A cross of two heterozygous (hybrid) individuals for one trait.
  • Example Aa × Aa
    • A = dominant allele
    • a = recessive allele

Result = 1 : 2 : 1

• True – breeding: organisms that are homozygous for a particular trait or set of traits and produce like offspring.
• Purebred: organisms descended from ancestors of a particular type, or breed.

Complete Dominance

• Type of inheritance in which heterozygous individuals and homozygous dominant individuals show the same phenotype
  • Example: B = dominant allele for brown hair

b = recessive allele for blond hair

Heterozygous = Bb = brown hair

Homozygous dominant = BB = brown hair

‘B’ is completely dominant over ‘b’

Example 1: Monohybrid Cross

T: allele for tall plants; t: allele for short plants

• A heterozygous tall plant is crossed with a short pea plant.
  • Q1: What are the genotypes of the parents?
  • Q2: What are the genotypes and phenotypes of the offspring of the F₁ generation?

Heterozygous tall parent

• Genotype = Tt

Homozygous short parent

• Genotype = tt
• To predict the genotypes and phenotypes of the offspring, we must cross the parents:

P generation: Tt × tt

• Complete the Punnett square.

*Remember: The dominant allele is always written first

• Genotypes of the offspring (F1 generation):
  • Two are Tt
  • Two are tt
  • Genotypic ratio is 2:2
    • Can be simplified to 1:1
    • The genotypes correspond to the following phenotypes:
  • Tt = tall plant
  • tt = short plant
  • Phenotypic ratio is also 1:1

Test Cross

• Used to distinguish between homozygous dominant and heterozygous individuals
• Example:
  • P = Purple flower
  • p = white flower

If you found a purple flower, how would you know if its genotype is PP or Pp?

• We know that a white flower will have the ‘pp’ genotype
• If we cross a white flower with the purple flower, we can tell whether the purple flower is ‘PP’ or ‘Pp’
  • PP = 100% purple flowers in F1 generation
  • Pp = 50% purple flowers and 50% white flowers in F1 generation

• Punnett squares allow you to see all possible combinations of gametes from a set of parents.
• Monohybrid crosses focus on one trait.
• Test cross is used to determine unknown genotype one trait

Dihybrid Crosses

• Cross of two individuals that differ in two traits
  • Example YYRR × yyrr

Law of Independent Assortment

• The inheritance of alleles for one trait does not affect the inheritance of alleles for another trait.
• Offspring may have new combinations of alleles that are not present in either parent.

Example question:

• A male and female guinea pig are both heterozygous for fur color and fur texture.
• Both dark fur (D) and rough fur (R) are dominant traits.
  1. What are the recessive traits and what letters do you use for them?
  2. What are the parent phenotypes?
  3. Determine the frequency of offspring that are homozygous for both traits.
  4. Determine the frequency of offspring that have rough dark fur.
  5. Determine the frequency of offspring that express both recessive traits

1. What are the recessive traits and what letters do you use for them?

• Dominant traits are:
  • Dark fur (D)
  • Rough fur (R)
  • Recessive traits must be:
  • Light fur (d)
  • Smooth fur (r)

2. What are the parent phenotypes?

• Both parents are heterozygous for both traits, so their genotypes are:

Parental Genotypes: DdRr × DdRr

Parental Phenotypes: dark, rough fur

3. Determine the frequency of offspring that are homozygous for both traits?

• Determine all possible gametes from each parent:

DdRr × DdRr

Each parent can produce four possible gametes:

DR, Dr, dR, and dr

• Place the gametes of each parent along the columns and rows of the punnett square and complete the possible crosses

There are only 2 individuals homozygous for color and texture: DDRR and ddrr

The proportion of offspring purebred for these traits is 2/16 or 1/8

4. Determine the frequency of offspring that have rough, dark fur

• The following offspring have rough, dark fur:
  • DDRR, DDRr, DdRR, and DdRr
• There are 9 individuals with this genotype.
  • Therefore, 9/16 of the offspring will have rough, dark fur.

5. Determine the frequency of offspring that express both recessive traits

• Only one offspring is homozygous recessive (ddrr).
• Thus, 1/16 of all the offspring will have light, smooth fur.

Check your solution

• If each parent is DrRr, a cross will produce 9 possible genotypes in the offspring:
  • DDRR, DDRr, DdRR, DDrr, DdRr, Ddrr, ddRR, ddRr, and ddrr
• The phenotypic ration of the offspring are:
  • 9/16 dark and rough fur
  • 3/16 dark and smooth fur
  • 3/16 light and rough fur
  • 1/16 light and smooth fur

(9:3:3:1)

Traits that do not follow a Dominant – Recessive pattern

Incomplete Dominance

• Neither allele controlling the trait is dominant
  • Results in blending of the two traits
  • Only capital letters are used to represent alleles
• Example: Snapdragons
  • Red flower × White flower = Pink flower
    • Both white and red flowers are homozygous
    • Pink flowers are heterozygous
• Letters R and R’ are used rather than R and r OR with superscripts (as shown in the image above)
  • Red flower = RR
  • White flower = R’R’
  • Pink flower = RR’

Co-Dominance

• Both alleles for a trait are always expressed (both are dominant).
• Both alleles are expressed in the heterozygous individual, so that they appear to have both types of gene expression.
• Example: Roan Cows
  • Heterozygous Roan Cows have both the red and white colour of the pure-breed Cows
• Different capital letters are used.
  • Red hair colour RR
  • White hair colour WW
  • Roan hair colour RW
• Human AB blood type is an example of co-dominance, as the blood cells have both A and B proteins in their cell membrane.

Epistatsis

• When a trait depends on the alleles of two different genes. The phenotype expression depends on 4+ alleles in combination (instead of the usual 2)
• E.g. Horse coat colouring is determined by both the "brown coat gene" (B and b), recessive giving tan coats, and the hair pigment gene (C and c) which only allows pigment formation in the coat if the dominant gene is present.

• Therefore:
  • BBCC, BBCc, BbCC, BbCc = Brown coats
  • bbCC, bbCc = Tan horse
  • BBcc, Bbcc, bbcc = white horse *(recessive condition in 'c' prevents colour formation in their fur)

Pleiotropy

• When one gene has multiple effects on the phenotype of the individual.
  • e.g. Mendel observed that pea plants with red flowers often had red coloured flowers, suggesting that the red flower gene affected leaf colour
  • e.g. Albino individuals have a gene combination that prevents pigment from forming in their skin and hair, and may also cause a modification of their eye nerve that causes them to be afflicted with crossed eyes.

Multiple Alleles

• Some genes have more than two forms (alleles)
• When the gene for a trait comes in more than 2 alleles the possible number of genotypes increases.
• Example: human blood types
• Human blood type is controlled by 3 alleles that combine into 4 blood types.
  • 3 alleles: A, B, O
• Each person has 2 out of 3 alleles.
• The 3 alleles are: I^A, I^B, i.

• Alleles I^A and I^B are dominant over i.
• I^A and I^B are co – dominant and are expressed equally.
• A: I^AI^A or I^Ai Red blood cells have A proteins in their cell walls
• B: I^BI^B or I^Bi Red blood cells have B proteins
• AB: I^AI^B Red blood cells have both A and B proteins
• O: ii Red blood cells do not have A, nor B proteins. (originally intended to be labelled zero-type blood)

• Evolutionarily: Three different theories revolve around the ABO blood type system.
  1. O type blood may represents the original gene, which over time mutated into the A gene for one group of humans and a separate group of humans evolved the B type protein, when these groups were reunited the AB genotype was born. This explains why O type is the most common and A and B are geographically separated.
  2. A-type was the original gene, that mutated into the O gene by a defect mutation. A different mutation either changed the A into B or O into B. This explains the overall distribution of blood types world wide (A the most common, O the second, B third, AB least).
  3. It may be that ABO genes were inherited from ancestral species, and the O-type blood is a mutated form of these genes that mutated multiple times through human history. This is consistent with the fact that other apes and mammals also have ABO genes.

Example problem:

• If a woman has blood type AB, and a man has blood type A, what possible blood types can their children have?
  • Mother: AB
    • Genotype = I^AI^B
  • Father: A
    • Genotype = I^AI^A or I^Ai
  • You must make the following crosses:
    • I^AI^B × I^AI^A
    • I^AI^B × I^Ai
    • Set up the Punnett Squares for these two crosses

Lethal Genes

• Some lethal traits show up in only the homozygous cases
  • Homozygous dominant or homozygous recessive
• Ex: the dominant allele is lethal when in the homozygous state
  • Y = yellow; y = nonyellow
  • If two heterozygous parents mate, 25% of the offspring could be homozygous dominant and would therefore die.

Epigenetic Traits

• Under certain external or environmental factors genes may be switched on and off, or the read of these genes may be changed.
• Additionally DNA may become chemically modified
  • The list of mechanisms is very extensive
• This can cause an inheritable permanent change in the DNA sequence
• This creates a “cellular memory”
• Studies have suggested many possible effects:
  • Anxiety, risk-taking, stress, learning and memory
    • E.g. Fear of spiders, due to an ancestor being traumatized by spiders
• May explain some aspects of:
  • aging, mental illness, diseases, addiction
    • E.g. study showed children of women who smoked marijuana had a higher rate of addictive personality traits
• Epigenetic traits collected during a lifetime may not be inherited, and continue to be modified through daily living
• They are most likely to occur under extreme stress (i.e. they are relatively rare)
• Caution: Epigenetics is a growing field of study, and new results must be regarded critically (poor science can show untrue results)

Sex Linked Traits

So far:

• We have only looked at traits that are inherited autosomally
  • Traits carried on autosomes
  • Males are just as likely to inherit the trait as females
  • Traits can also be carried on sex chromosomes

Biological sex differentiation in humans

• Normal human diploid chromosome number is 46
  • 23 pairs of chromosomes; one of each pair coming originally from each of the individual’s parents
• During fertilization, when 2 haploid gametes meet, the diploid chromosome number is restored in the zygote.

Genetically Male or Female?

• If an individual possesses two X – chromosomes (XX) it is a female.
• If an individual possesses one X – chromosome and one Y – chromosome (XY) it is a male.

Recall

• Meiosis produces gametes that possess only one copy of each type of chromosome.
  • Females produce only X egg cells
  • Males produce X and Y sperm cells
• The genotype of the sperm cell determines the sex of the child.
  • The mother always contributes an X
  • The father can contribute either an X or a Y

We all start out female!

• First 6 weeks – embryo develops as a female.
• In the 7^th week, genes on the Y – chromosome trigger the release of male hormones
  • Stimulates the development of male reproductive organs

Sex-linked Genes

• Since the X chromosome is longer than the Y chromosome it can carry more genes on it.
• This leads to sex – linked traits
  • Only found on the X -chromosome
• Sex – linked genes follow the dominant/recessive pattern but different notions are used

• Example: in the fruit flies, eye colour is a sex – linked trait. Red eyes are dominant to white eyes.
  • R = red eye
  • r = white eye
• If the recessive gene is r, a female carrying one copy is X^RX^r and a male is X^rY.
• By using X and Y, it is easier to remember that it is a sex – linked traits.
• A homozygous red eyed Female is mated with a White eyed male

Hemophilia

• Sex – linked disorder in where the blood doesn’t adequately clot when an injury occurs.
  • X^H = normal
  • X^h = hemophilia

Females: X^HX^H, X^HX^h = normal; X^hX^h = hemophilia

Males: X^HY = normal; X^hY = haemophilia

• Males are affected more often than females since the only have one X – chromosome.

*Traits are not associated with the Y – chromosome.

Example

• A woman with normal vision but who is a carrier of colour – blindness and a man with normal vision get married.
• If red – green colour – blindness is a recessive sex – linked disorder, what is the chance that they will have children who are colour – blind?
  • X^H = normal vision
  • X^h = colour – blindness

Woman: X^HX^h

Man: X^HY

• 2 females
  • Both normal vision
• 2 males
  • One normal vision
  • One colour - blind
• Phenotypic ratio:

3 normal : 1 colour - blind

Genetic Mutations and Genetic Testing

Crossing Over

• Crossing over during Prophase I of meiosis creates the genetic variability in offspring
• Ensures variation in gametes
  • Makes you different from your parents and siblings

Random Fertilization

• Any sperm can fuse with any egg (ovum)
  • Adds to genetic variation
  • 8.4 million possible chromosome
  • Approximately 70 trillion diploid combinations

Genetic Mutations

• Mutations are changes in the genetic information of a living cell
  • Some have little or no effect in the organism; however, some are lethal.
  • When they occur in gametes, they are passed on to future generations.
    • Adds to genetic variability

Chromosome Mutations

• Significant change in the physical structure of chromosomes.

Deletion

• A portion of the chromosome is lost.
  • Advantage – elimination of detrimental genes
  • Disadvantage – loss of critical genes is lethal
  • Example: Cri – du – chat (cat’s cry)
    • Abnormally developed larynx (voice box) makes an infant’s cries sound like a cat’s meow.

Translocation

• A segment of one chromosome is moved to another chromosome.
  • Advantage – enormous genetic changes; evolutionary advantage
  • Disadvantage – may activate genes that cause cancer
  • Examples: Thyroid cancer, leukemia, schizophrenia

Inversion

• A gene segment is inverted (reversed)
  • Advantage – can provide backup genes
  • Disadvantage – may interfere with chromosome separation
  • Example: Some forms of autism.

Duplication / Amplification

• A gene sequence is repeated one or more times.
  • Advantage – increase genetic diversity
  • Disadvantage – reduced fertility
• Example: Fragile – X Syndrome
  • Duplication in the X - chromosome.
  • Results in a spectrum of intellectual disabilities

Chromosome Inactivation

• Since females have two X- chromosomes in every cell and males only have one X- chromosome, one of the X – chromosomes in each female cell is inactivated (Barr body).
  • Prevents females from having twice the number of X-chromosome genes as males.
  • Inactivation is random.

• Example: calico coat colour only occurs in female cats.
  • Black and orange alleles for fur colour are located on the X – chromosome
    • Black patch = X – chromosome carrying allele for orange fur was inactivated; shows black fur colour.
    • Orange patch = X – chromosome carrying alleles for black fur was inactivated; shows orange fur colour.

Mistakes can also occur in the formation of gametes

Nondisjunction

• Can occur in
  • Autosomes (chromosomes not involved in sex determination)
  • Sex – chromosomes (X- or Y- chromosomes)
• Trisomy: Inheriting an extra chromosome
• Monosomy: Inheriting one chromosome instead of a pair of chromosomes

• Occurs when chromosomes or chromatids do not separate as they should during meiosis
  • Gametes have either too many or too few chromosomes
    • If involved in fertilization, the embryo has either extra or fewer chromosomes.
    • Rarely survive (miscarried/spontaneously aborted).

Karyotypes

• Photograph of all chromosomes in a somatic cell of an individual.
  • Analyzed to determine if any chromosomal abnormalities has occurred.
  • Particularly searching for nondisjunction of the chromosomes

Example (left): Male without nondisjunction

• 22 pairs of autosomes
• 1 pair of sex chromosomes
  • In this case, one X- and one Y – chromosome

Autosomal Nondisjunction

• Nondisjunction which results in missing or extra autosomal chromosomes
• Typically a fatal condition for the zygote
  • A large number of genes located on each autosome
  • Results in cells missing essential structures, preventing viability

Examples of viable autosomal non-disjunction

• Down syndrome (Trisomy 21) – not lethal
  • Three copies of chromosome 21.
  • Abnormal chromosome number of 47.
  • Various characteristics, Including mental retardation, heart problems, characteristic facial features
  • Occurs in 1 in every 800 children in Canada.

*Syndrome: a condition characterized by a set of associated symptoms

Nondisjunction of sex-chromosomes

• If nondisjunction occurs in an egg ell:
• If these egg cells fuse with normal sperm cells, the sex chromosomes in the zygote would have one of the following genotypes:
  • XXX
  • XXY
  • XO
  • YO

XO – Turner syndrome

• Egg cell contributes no sex chromosome; sperm cell contributes one X chromosome
• Female
  • Short in height
  • Webbing in the skin of the neck
  • Some mental impairment
  • Underdeveloped ovaries and breasts
  • Little body hair
  • Sterile
  • 1 in every 10 miscarriages

XXX – Triplo-X

• Egg cell contributed two X chromosomes; sperm cell contributed one X chromosome.
• Female
  • No physical abnormalities
  • Mental retardation
  • Fertile
  • Children are usually normal

YO

• This monosomy has never occurred.
• An egg cell with no sex chromosome cannot be successfully fertilized in vivo by a sperm cell containing a Y – chromosome.
• A cell that does not contain at least one X chromosome cannot survive.

XXY – Klinefelter Syndrome

• Egg cell contributes two X – chromosomes; sperm cell contributes one Y chromosome.
• Male
  • Abnormal development of the testes
  • Most are sterile
  • Enlarged breasts
  • Very little body hair
  • Some mental impairment

Genetic Testing

• Genetic research has resulted in rapidly increasing amounts of genetic knowledge.
• Not all genetic disorders and diseases are fully understood.
• Many patients of genetic disorders and diseases do not know whether their conditions
  • Could have been prevented
  • Could have been detected or treated earlier
  • Could be passed on to some or all of their children

Karyotype analysis

• Can be used to identify nondisjunctions (downs syndrome, Triple-X, Turner syndrome…)
• If a Karyotype indicates that the fetus has a disorder, the parents are counselled about what they can expect and what their options may be.

How are Karyotypes made?

• First a sample of an individual’s body cells is needed
  • Adult – white blood cells are used.
  • Fetus – cells from amniotic fluid are used (amniocentesis)
  • Cells are allowed to divide and grow in a solution in lab.

• Chromosomes are most easily seen during metaphase of mitosis.
• A chemical (colchicine) stops cell division.
• A slide is prepared and cells are analyzed.
  • Stained for easier visibility.
• Cells are photographed to produced a Karyotype.

Amniocentesis

• An ultrasound-guided needle is inserted into the pregnant woman’s abdomen
  • Small amount of amniotic fluid is removed and analyzed.
  • Can detect chromosomal abnormalities, like Trisomy 21.
• Approximately 1 in 200 pregnancies end in miscarriage after this procedure (0.6% failure rate)
• This number is higher earlier in the pregnancy, when the fetus is more mobile

Ultrasound

• Sound waves are produced from a transducer that is moved over the pregnant woman’s abdomen.
  • Produces images of the fetus on a screen
  • Allows for assessment of the growth and development
• Can identify various abnormalities that may be treatable before birth.

Umbilical cord sampling

• A sample of the fetus’s blood is taken from the vein in the umbilical cord.
• Tested to look for disorders, such as hemophilia and Anemia.
• 1 in 50 pregnancies ends in miscarriage after this procedure.