1 chapter 2 heredity & prenatal development (part 1)

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Chapter 2

Heredity & Prenatal Development

(Part 1)

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What are the Mechanisms of Heredity? - Egg and Sperm!

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The Basics: Each woman’s egg

cell contains 23 chromosomes.

Each male sperm cell also 23.

At conception, the egg and sperm unite, for a total of 46 chromosomes.

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What Does Conception Look Like?

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Chromosomes: The first 22 pairs of

chromosomes are called Autosomes

The 23rd pair are called Sex Chromosomes.

Chromosomes, cont. Autosomes: Pairs that look alike

and possess genetic information concerning the same set of traits.

Sex Chromosomes: Pairs that look different from the other chromosomes, and which determine our sex.

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23 and 23 Combine!

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Sex Chromosomes: We all receive an X chromosome

from our mother. The father supplies either an X or Y

chromosome, which determines the gender.

XX= Girl XY= Boy

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Genetics 101: Inside each cell of

our body is a nucleus.

The nucleus contains: Chromosomes.

Each chromosome contains thousands of segments called genes.

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Genetics 101, cont.: Genes – Are segments of larges strands of

DNA located along the chromosomes.

– Genes determine what traits we will have.

-- Most human behaviors/abilities are believed to be affected by combinations of genes

DNA – Resembles a twisted ladder. – The sequence of the rungs

determine the genetic instructions to grow wings, fins, skin, or scales.

Our Complete Set of Genes Makes Up Our Heredity or Our:Genotype:

- The genetic makeup of an individual. - Our complete set of genes

Phenotype:- Genetic instructions

combined with environmental influences.-The observable characteristics of an individual (physical, behavioral, psychological features)

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How Do Genes Determine Traits?

Traits are determined by pairs of genes (one from the mother and one from the father) called Alleles.

When both Alleles are alike the child is Homozygous for that trait.

When both Alleles are different, the child is Heterozygous for that trait.

The Alleles can be either dominant or recessive.

A dominant allele is always followed, if paired with a recessive allele.

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Dominant/Recessive Alleles: Dominant w/ Dominant:

Dominant trait expressed Dominant w/ Recessive:

Dominant trait expressed Recessive w/Dominant:

Dominant trait expressed Recessive w/ Recessive:

Recessive trait expressed.

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Dominant-Recessive Inheritance

PKU, eye color, etc.

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What is a Carrier? Someone with one recessive allele

for a disease or trait is often called a “carrier.”

In the case of carriers for genetic disease, the person is fortunate to have a dominant gene that cancels it out.

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X-Linked Inheritance Males are more

likely to be affected because their sex chromosomes do not match.

Because the Y chromosome is 1/3 shorter than the X chromosome, it lacks the corresponding genes to override those on the X.

Ex: Hemophilia, Color Blindness

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Did you know: Rates of miscarriage, infant &

childhood deaths, birth defects, learning disabilities, behavior disorders, and mental retardation are all higher for boys.

(Mother nature adjusts for this: There are 120-150 boys born for every 100 females. Cool huh?)

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Disorders Caused by Chromosomal Abnormalities: Down Syndrome(Most common)

Child born with an extra chromosome on the 21st pair.

Results in characteristicfacial features anddeficits in motor and

cognitive development.

Disorders Caused by Chromosomal Abnormalities, cont.

Sex-Linked Chromosomal Abnormalities:Child born with an abnormal number of sex chromosomes.

a. XYYb. Klinefelter Syndrome (XXY) c. Turner Syndrome (Single X) d. XXX

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Disorders Caused by Genetic Abnormalities: PKU: (recessive allele) an disorder causing

the child no not metabolize phenylalanine. This amino acid builds up in the brain and causes Mental Retardation.

Sickle Cell Anemia: (recessive allele) common in African Americans. Red blood cells take on the shape of a sickle and clump together. Clumping blocks blood and O2 supply.

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Disorders Caused by Genetic Abnormalities, cont.

Tay-Sachs Disease (recessive allele) A fatal disease in Jewish families. Causes the CNS to degenerate and the person loses control over their muscles. Die by the age of 5.

Huntington’s Disease (dominant allele) A progressive degenerative disorder. As person ages it causes muscle weakness, loss of personality and intellectual functioning.

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Why are their fewer dominant allele genetic abnormalities?Guess:

Because most result in early death, before the person can reproduce.

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How are Twins Created?Fraternal/Dizygotic: A woman ovulates two eggs

which are fertilized with 2 different sperm cells.

Are just like any other siblings. Runs in families.

Identical/Monozygotic:

One fertilized egg that divides into two individuals.

This is more rare and considered a fluke of nature.

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Who Has The Highest Rate of Dizygotic Twins? 2 per 1,000 births in: Asians 8 per 1,000 births in: Whites 50 per 1,000 birth in: Blacks Rates are also high in: Latinos Older mothers have a higher incidence

**Did you know: The female partner is the one who influences the incidence of DZ twins. Why?

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Did You Know? Nearly half of all fertilized eggs abort

spontaneously within 2 weeks, primarily because of abnormal autosomes.

The risk of chromosomal abnormalities increases with parental age.

After age 35 the overall rate of chromosomal abnormalities rises sharply, from 1:90 to 1:20 pregnancies at age 43.

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What are the Choices A Couple Has Who Carry a Genetic Disorder?

Genetic counseling

Prenatal diagnosis and fetal medicine

Adoption

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Prenatal Diagnostic Methods

Amniocentesis Chorionic Villus Sampling Fetoscopy Ultrasound Pre Implantation Genetic

Diagnosis Maternal Blood Analysis

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Amniocentesis and Chorionic Villus Sampling:

Amniocentesis: 14-16 wks Cells from amniotic fluid

CVS: 9-12 wksCells from placenta

(carry 1/100 miscarriage rate)

Fetoscopy:

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From the outside looking in!

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Pre-Implantation Genetic Diagnosis

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Maternal Blood Analysis

Can reveal the presence of mostly recessive genes for many disorders.

Alpha Fetoprotein can detect neural tube defects. (but if mom <35, very high false positive rate)

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Reproductive Technologies Artificial

Insemination In Vitro

Fertilization Surrogate Mother Donor Eggs/Sperm Donor Embryo

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Did You Know? If your child has a prenatal

problem, such as spina bifida/twin to twin transfusion it can be corrected with fetal surgery?

It is usually done in the 8th or 9th month of pregnancy.

Fetal Surgery:

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Open Fetal Surgery:

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Average Costs: Artificial Insemination: $300-$700 per

cycle. (w/meds & u/s $1,500 to $4,000) IVF: $10,000-$15,000 per cycle. Surrogacy: $40,000-$80,000 per cycle Domestic Adoption: $15,000 to $30,000 International Adoption: $20,000-$40,000 Foster Adoption: Zero to $2,500

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Average Costs, cont. Donor Sperm: Anonymous $380-

$535 per vial,Open $490-$645 per vial

Donor Egg: $15,000 and $20,000 per cycle.

Embryo Adoption: Free

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