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Genetic Control of Growth & Maturation

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Page 1: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Genetic Control of Growth & Maturation

Page 2: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Gregor Mendel (1822-1884)

Mendel studied the inherited traits of pea plants.

Page 3: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Gregor Mendel (1822-1884)

From his observations Mendel deduced that:– Each characteristic must be determined by a

hereditary factor– There is a pair of hereditary factors; one from

each parent

Page 4: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

The law of uniformity: When two homozygotes with different alleles are crossed, all the offspring are identical and heterozygous.

The law of segregation: Each individual possesses two genes for a particular characteristic, only one of which can be transmitted.

The law of independent assortment: Members of different gene pairs segregate to offspring independently of one another.

Gregor Mendel (1822-1884)

Page 5: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Mendel’s Observations

Generation 1:– Yellow Round x Green Wrinkled– All Yellow Round offspring

Generation 2:– Yellow Round x Yellow Round

Generation 3:– Yellow Round, Yellow Wrinkled, Green Round.

Green Wrinkled

Page 6: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Explanation of Mendel’s Observations

Generation 1:– Yellow Round (YYRR) x (Green Wrinkled (yyrr)

Generation 2:– Yellow Round (YyRr) x Yellow Round (YyRr)

Generation 3: – 9 Yellow Round (YYRR or YyRr)– 3 Yellow wrinkled (Yyrr or Yyrr)– 3 Green Round (yyRR or yyRr)– 1 Green Wrinkled (yyrr)

Page 7: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Pea Experiment

Click on the link below when you are connected to the internet

Pea Soup Website

Page 8: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Gene

Page 9: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Alleles

The two copies of each gene are called alleles, which may be identical (AA and aa) or different (Aa).

Page 10: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Homozygous

Refers to the state of carrying identical alleles at one or more gene loci (e.g. AABB or aabb).

Page 11: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Heterozygous

Refers to the state of carrying different alleles at one or more gene loci (e.g. AaBb).

Page 12: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Law of segregation is that alleles segregate, or separate, when the F1 generation produces gametes.

Alleles reside at specific loci, or sites, on the chromosomes within the DNA molecule.

Segregation of Alleles

A pair of homologous chromosomes contains two alleles at each locus and during gamete formation of meiosis, each gamete receives only one member of each homologous pair of chromosomes. Therefore, each gamete also receives only one allele of a particular locus.

Page 13: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

CytogeneticsThe study of Chromosomes

1903 Sutton and Boveri independently proposed that the vehicle of hereditary factors or genes were the thread-like structures seen by light microscopy in the nucleus of each cell.

Chromosomes because of their affinity to take up certain stains (Greek: chroma, colour; soma, body).

Chromosomes are only being seen during the metaphase stage of cell division when they are maximally contracted.

Plant Chromosomes: von Nägeli in 1842. Animal Chromosomes: Flemming (mitosis) 1882.

Page 14: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

KaryotypeChromosome Complement of the Cell (1956)

Karyotyping is the process of imaging the chromosomes of the cell

23 pairs of chromosomes 44 autosomes + 2 sex

chromosomes 46, XX = Normal female 46, XY = Normal male

Page 15: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Genotype

The genetic make up of the individual. Typically, one refers to an individual's genotype

with regard to a particular gene of interest It refers to what combination of alleles the

individual carries (either homozygous or heterozygous).

Page 16: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Phenotype

Any feature or characteristic of an organism or any group of characteristics (e.g. metabolism, physiology, or morphology).

The phenotype is the result of the interaction of the gene and environmental components.

Page 17: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Human Genome Project

The Human Genome Project (HGP) aimed to map and understand of all the genes of human beings.

In 1911, Alfred Sturtevant, then an undergraduate researcher in the laboratory of Thomas Hunt Morgan, realized that he could - and had to, in order to manage his data - map the locations of the fruit fly (Drosophila melanogaster) genes whose mutations the Morgan laboratory was tracking over generations. Sturtevant produced the very first gene map.

Page 18: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Human Genome Project

The hereditary material of all multi-cellular organisms is the famous double helix of deoxyribonucleic acid (DNA), which contains all of our genes.

DNA, in turn, is made up of four chemical bases, pairs of which form the "rungs" of the twisted, ladder-shaped DNA molecules. All genes are made up of stretches of these four bases, arranged in different ways and in different lengths.

Page 19: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Human Genome Project

By February 2003 HGP researchers fully mapped the the human genome.

– determining the order, or "sequence," of all the bases in our genome's DNA;

– making maps that show the locations of genes for major sections of all our chromosomes;

– and producing what are called linkage maps, through which inherited traits (such as those for genetic disease) can be tracked over generations.

The HGP has revealed that there are probably somewhere between 30,000 and 40,000 human genes 50,000 genes to as many as 140,000).

National Human Genome Research Institute

Page 20: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Genetic Variation Program

Most of any one person's DNA, about 99.5 percent, is exactly the same as any unrelated person's DNA. Differences in the sequence of DNA among individuals are called genetic variation.

Genetic variation explains some of the differences among people, such as eye color and blood group. Genetic variation also plays a role in whether a person has a higher or lower risk for getting particular diseases.

Single gene differences in individuals account for some traits and diseases, such as the ABO blood group, cystic fibrosis and sickle cell disease.

Page 21: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Genetic Variation Program

More complex interrelationships among multiple genes and the environment are responsible for many common diseases, such as diabetes, cancer, stroke, Alzheimer's disease, Parkinson's disease, depression, alcoholism, heart disease, arthritis and asthma.

The Genetic Variation program supports research on genetic variation and how it relates to diseases, responses to drugs and environmental factors.

Page 22: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Genetic Expression

If all cells come from the one original zygote, how can the cells in the body vary so much

Some genes are permanently switched on – enzymes required for respiration etc

Some genes become switched off because they are no longer required to be functional in that particular cell or tissue.

Insulin is produced in pancreas cells, which must have the gene that codes for insulin switched on, and genes that are un-related to the role of the pancreas can be switched off.

Some other genes that will be functional during specialisation determine the physical characteristics of the cell, i.e. long and smooth for a muscle cell or indented like a goblet cell

Page 23: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Height

Polygenetic control

HT

186.0182.0

178.0174.0

170.0166.0

162.0158.0

154.0150.0

146.0

Height (Women)800

600

400

200

0

Std. Dev = 6.22

Mean = 161.0

N = 5782.00

Page 24: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Parental Size

Average height of siblings approximates average height of parents– Parental stature adjusted growth curves

Birth size poorly correlated with adult size Birth size correlated to mother’s size

Page 25: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Walton and Hammond (1938) Crossed large Shire horses with small Shetland ponies.

Page 26: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Walton and Hammond (1938)

Offspring of the crosses delivered to Shire dams were heavier than that of pure Shetland ponies, but below that of pure Shire offspring.

In contrast, the reciprocal cross-delivered to the Shetland dam was of the same weight at birth as the Shetland purebred foal.

The Shetland mother was able to down regulate the in utero growth of her foal sired by the much larger Shire horse, while the in utero environment provided by the larger Shire mother facilitated enhanced growth.

Page 27: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Allen et al. 2004

Allen et al. (2004) Confirmed the original observations of Walton &

Hammond (1938) that a genetically large foal cannot reach its normal birthweight when gestated in a uterus that is smaller than normal, and the runting effect persists throughout life.

Furthermore, that genetically small foals will be born heavier than usual if gestated in the uteri of larger than normal mares and, similarly, this increased size persists to adulthood

Page 28: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

14 months of age

Tb-in-P vs Tb-in-Tb

3 years of age

P-in-Tb vs P-in-P P-in-P vs P-in-Tb

Tb-in-P vs Tb-in-Tb

Page 29: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Allen et al. 2004

Clear maternal size influence at birth Lasting effect in postnatal development Larger mother provided

– Larger placental area– Greater microcotyledon density

Page 30: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Skin Colour

Skin colour depends on the degree of melanin found in skin cells.

There are two genes that control the production of melanin, each of which has a dominant and recessive expression.

16 combinations of genotype when coding for skin colour, as seen below.

Page 31: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Skin Colour

# Genotype1 M1M1M2M22 M1M1M2m23 M1M1m2m24 M1m1m2m25 m1m1m2m2

PhenotypeBlack SkinDark Brown SkinBrown SkinLight Brown SkinWhite Skin

A person is born with one of five colours. External factors such as the UltraViolet light from the sun modify the genetic expression of colour.

Page 32: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Sex Linked Inheritance

A recessive trait on the X chromosome can find expression in a male

Page 33: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Sex Linked InheritanceFather’s contribution determines the sex of the child.

Page 34: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Hemophilia A

Mainly exhibited in males, due to recessive gene on X chromosome.

Only exhibited in double recessive females. Sons of hemophiliac males will not have the

gene All daughters of male hemophiliacs will be

carriers

Page 35: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Genetic DisordersChromosomal Disorders

Numerical (Aneuploidy) due to nondisjunction.

Structural chromosomal due to a break in chromosome(s).

Page 36: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Genetic DisordersChromosomal Disorders

– Numerical (Aneuploidy) due to nondisjunction1st or 2nd division of meiosis. An extra copy of a

chromosome (trisomy) or a missing copy of a chromosome (monosomy).

Aneuploidy can also occur at mitosis after conception and leads to chromosomal mosaicism, a mixture of two or more cell lines each having a different number of chromosomes.

Page 37: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Genetic DisordersMendelian Disorders

Caused by a mutant allele or pair of mutant alleles at a single gene locus.

– Either inherited or due to a new mutation.

Autosomal dominant or autosomal recessive. – Homo vs Heterozygous, Male vs Female?

Variable expressivity. Penetrance

– percentage of individuals exhibiting symptoms or signs– E.g. reduced penetrance in neurofibromatosis, a disorder

characterized by multiple brown skin patches and benign growths.

Page 38: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Genetic DisordersMendelian Disorders

Autosomal recessive disorders only manifest in the homozygote.

Both sexes can be affected and heterozygotes (or carriers) are normal phenotypically.

Most individuals affected by an autosomal recessive disorder are born to healthy carrier parents.

– 25% chance of homozygous normal– 50% chance of unaffected heterozygote carriers– 25% chance of having a homozygous affected offspring..

Cystic fibrosis is an autosomal recessive disorder

progressive lung damage and poor growth

Page 39: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Genetic DisordersMendelian Disorders

Autosomal recessive disorders only manifest in the homozygote.

Both sexes can be affected and heterozygotes (or carriers) are normal phenotypically.

Most individuals affected by an autosomal recessive disorder are born to healthy carrier parents.

– 25% chance of homozygous normal– 50% chance of unaffected heterozygote carriers– 25% chance of having a homozygous affected offspring..

Cystic fibrosis is an autosomal recessive disorder

progressive lung damage and poor growth

Page 40: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Genetic DisordersMendelian Disorders

Autosomal recessive disorders only manifest in the homozygote.

Both sexes can be affected and heterozygotes (or carriers) are normal phenotypically.

Most individuals affected by an autosomal recessive disorder are born to healthy carrier parents.

– 25% chance of homozygous normal– 50% chance of unaffected heterozygote carriers– 25% chance of having a homozygous affected offspring..

Cystic fibrosis is an autosomal recessive disorder

progressive lung damage and poor growth

Page 41: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Genetic DisordersMultifactorial Disorders

Multifactorial disorders occur in more than one member of the family but do not follow a mendelian pattern of inheritance.

Interaction between environmental factors and a number of genes

Cleft lip, palate, spina bifida and common disorders in adults (e.g. diabetes mellitus, cancer, schizophrenia) are thought to be multifactorial in origin.

The risk for an individual of developing a multifactorial disorder is determined by the number of affected members in the family and the relationship to the patient.

Page 42: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Chromosome Aneuploidy

Aneuploidy = wrong number Sex Chromosome Aneuploidies

– Wrong complement of sex chromosomes– E.g. 47,XXX; 45,X0

Autosomal Aneuploidies– Trisomy 21: Down Syndrome

Page 43: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

47, XXX

1 : 960 Normal in appearance Usually fertile 15-25% are mildly mentally retarded Occurs due to nondisjunction in meiotic division

of female

Page 44: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants
Page 45: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Turner’s Syndrome

•1 : 2,500 live female births (1:5,000 total live births).

•There are indications that as few as 1:50 45, X0 conceptions are born alive. The others spontaneously abort. This suggests that the monosomy tends to be lethal.

Page 46: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Turner’s Syndrome

"Webbing" of the neck is often seen at birth and beyond. – The skin between the mastoid

region and the shoulder expands before birth to cover a swollen jugular lymph sac.

– The swelling usually goes down before birth, but the excess skin persists as a redundant fold.

A broad, shield-shaped chest and widely spaced nipples are also typical in this syndrome.

Short for their age; as adults they rarely exceed 5 feet in height.

Page 47: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Turner’s Syndrome

Ovarian dysgenesis and are infertile.

Cardiovascular abnormalities.

Many have a low posterior hairline.

Behind siblings in intellectual development.

Poor sexual development internally and externally.

Page 48: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

45, Y0

Given that 45, X0 individuals exist, one might expect the viability of its male counterpart, 45, Y0. However, no such adults, children or embryos have been reported.

Indeed, Y0 or YY cells have never been observed. It has been suggested that these theoretically possible chromosome constitutions are incompatible with life, even with life as a very early embryo. Apparently there are genes necessary for life located on the X chromosome

Page 49: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Klinefelter Syndrome47, XXY

Incidence 1 : 1080

Page 50: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Klinefelter Syndrome47, XXY

Small testes, hyalinization of seminiferous tubules; aspermatogenesis

Often tall with disproportionately long limbs.

Intelligence is less than in normal siblings.

About 40% of these males have gynecomastia

Page 51: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

47,XYY “the criminal type”

Adults with 47, XYY syndrome may exhibit a pockmarked face owing to severe acne during puberty. Growth is often accelerated during mid-childhood, so adults with this syndrome are often very tall. Severe acne may develop in puberty, leading to a pock-marked face in adult life.

On the other hand, not all individuals are so affected by acne. Indeed, both physical abnormalities and behavioral aberrances may be absent.

Page 52: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

47,XYY “the criminal type”

Nevertheless, one study showed that among institutionalized male juvenile delinquents, one in 35 had a 47, XYY karyotype. This rate is 24 times the incidence of 47, XYY karyotype in all newborn males. On the basis of this, the association with behavioral problems is significant.

Page 53: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Down SyndromeTrisomy 21

Virtually all individuals with Down syndrome are mentally retarded, with the IQ most often in the 25 to 50 range.

Congenital malformations of the heart are present in over half of these persons, and there is a 15-fold increase in risk for developing leukemia.

Characteristic face and physique.

Page 54: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Down Syndrome - Trisomy 21

Risk increases with maternal age

Maternal Age

Incidence

20-24 1:1400

25-29 1:1100

30-34 1:700

35 1:350

37 1:225

39 1:140

41 1:85

43 1:50

45+ 1:25

Page 55: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Mosaicism

Two or more cell types containing different numbers of chromosomes.

This example is for Down Syndrome but it can occur for all aneuploidies.

Page 56: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Trisomy 18 – Edwards Syndrome

47, XX, +18 or 47, XY, +18 1 : 3,300 live births. It is more severe than Down

syndrome. Estimated that 95% of trisomy 18 fetuses abort

spontaneously. Of those born alive, 30% die within a month of birth, 50% by two months and only 10% survive the first year of life.

Failure to thrive, mental retardation. Half or more show growth deficiency and hypertonicity after the neonatal period. Over 130 abnormalities associated with trisomy 18 have been noted in the literature.

Page 57: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Trisomy 18 – Edwards Syndrome

Clenched fist and over lapping fingers. Edward syndrome babies exhibit an unusual posture of the hands. The hands are clenched with the index finger overlapping the next and the 5th over the 4th

Also common is "rocker bottom deformity" of the feet - prominent calcaneus bones and dorsiflexion, resulting in a convex plantar surface.

Short sternum, narrow pelvis

Page 58: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

47, XX, +13 or 47, XY, +13 1 : 5,000 live births, and the sex ratio is close to 1:1. Half of the infants with it die within a month of birth. Severe mental retardation and varying degrees of

incomplete development of the brain are characteristic.

Growth retardation, sloping forehead, eye and ear malformations.

Patau Syndrome - trisomy 13

Page 59: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Patau Syndrome - trisomy 13

Of the many abnormalities that can occur in this defect, the most consistent are cleft lip (60 to 80% of the cases), cardiac malformations (80%), and the brain defects coupled with severe mental retardation.

Almost all organ systems may show defects.

Page 60: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Patau Syndrome - trisomy 13

Because of the high mortality (only 18% survive the first year), coupled with severe organ defects including the brain, at least some pediatricians believe that no medical means should be employed to prolong the life of these individuals

Page 61: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Cri-du-chat Syndrome

In 1963, French geneticist Jerome Lejeune first described the syndrome noting the mewing, cat-like cry in affected newborns.

He was a pro-life pediatrician who discovered many connections between chromosome abnormalities and diseases.

He devoted a major part of his career treating children affected by Down’s syndrome.

Page 62: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Cri-du-chat Syndrome

46, XX, 5p- or 46, XY, 5p- 5p- indicates deletion of the short arm of

chromosome number 5. Deletion of the long arm would be abbreviated 5q-, q

indicating the long arm of this chromosome. Also present in 100% of the cases are microcephaly,

mental retardation and slow growth. Almost all exhibit optic hypertelorism (widely spaced

eyes), and 85% exhibit epicanthic folds.

Page 63: Genetic Control of Growth & Maturation. Gregor Mendel (1822-1884) Mendel studied the inherited traits of pea plants

Cri-du-chat Syndrome

Also present in 100% of the cases are microcephaly, mental retardation and slow growth.

Almost all exhibit optic hypertelorism (widely spaced eyes), and 85% exhibit epicanthic folds.

Common symptoms are webbing of the fingers and toes, abnormal motor skill development, and a single line in the palm of the hand, known as a Simian crease.

This is a rare condition, occurring about once in every 50,000 live births.