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CHDV1400-Chapter3.pptxChapter 3: The New Genetics
Alma Villanueva, MA
California State University, Los Angeles
Overview
Genetic Code
The Beginning of Life
Male & Female
Twins
Genotype & Phenotype
Disorders
Genetic Counseling
Genetic Code
Cells
Basic unit of life
Trillions!
Nucleus
Chromosomes
Thread– like structures made up of DNA & protein
23 pairs
DNA (Deoxyribonucleic acid)
2 strands twisted in a double helix
Chemical composition of molecules that contain the genes
Contains all of the information required to build/maintain the cell
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Genes
Small section of the chromosome
18,000 – 23,000 genes
Each gene provides a unique recipe to make a protein
4 bases
Code for your traits
A - adenine
T - thymine
C - cytosine
G – guanine
Only 4 possible pairs
A-T; T-A; C-G; G-C
http://mybrainnotes.com/brain-dna-behavior.html
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Allele
A variation of a gene
Example: the gene for eye color has several variations (alleles); an allele for blue eye color or an allele for brown eyes
Everyone inherits alleles from sperm & ovum
Genetic diversity
Distinguishes each person
Allows the human species to adapt to pressures of the environment
Genome
Full set of genes with instructions to make a living organism
Genomes exist for each species
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The Beginning of Life
Two Parents, Millions of Gametes
Gamete
Reproductive cell
Sperm or Ovum
Each contains 23 pairs
Zygote
Cell formed with union of Sperm & Ovum
Produce a new individual with 23 chromosomes from each parent
http://predictingbabygender.info/tag/intercourse-timing/
Matching genes
Genotype
Organism’s entire genetic inheritance, or genetic potential.
Homozygous (same zygote)
Two genes of one pair that are exactly the same in every letter of their code
Heterozygous
Two genes of one pair that differ in some way
Usually not an issue
Male of Female?
Humans usually possess
46 chromosomes
44 autosomes and 2 sex chromosomes
SEX chromosome = 23rd pair
Female – XX
Male – XY
Mother’s contain X
Father’s may have X or Y
X chrom. Is larger & more genes
Y contain SRY,
making male hormones & organs
Uncertain Sex
“ambiguous genitals,” = child's sex is not abundantly clear
a quick analysis of the chromosomes is needed, to make sure there are exactly 46 and to see whether the 23rd pair is XY or XX
shown here a baby boy (left) and girl (right).
Too Many Boys?
Is sex selection the parents’ right or a social wrong?
Preference for boys in many areas of world
Ways to prevent female birth
Inactivating X sperm before conception
In vitro fertilization (IVF)
Aborting XX fetuses
My Strength, My Daughter
slogan these girls in New Delhi are shouting at a demonstration against abortion of female fetuses in India
The current sex ratio of children in India suggests that this campaign has not convinced every couple.
New Cells
Within hours of conception
23 pairs of chromosomes carrying all the genes duplicate, forming two complete sets of the genome
Two sets move toward opposite sides of the zygote
the single cell splits neatly down the middle into two cells
By birth = 10 trillion cells
By Adulthood = 37 trillion cells
Stem Cells
Stem Cells
Results from early duplication and division
Are able to produce any other cell
Differentiation
Cells specialize
Placenta- organ that sustains the dev. Person through pregnancy
Sample of the placenta blood can be checked for genetic/chromosomal disorders
Research
Replicate & try to produce genes to fight diseases and other medical intervention
May cause havoc, causing cancer or death
Ethical issues
www.scientificamerican.com
Twins
MONOZYGOTIC TWINS
(Identical Twins)
1 in 250 conceptions
Originate from one Zygote that splits apart very early in development
Incomplete split results in conjoined twins
same genetic instructions but slight variations in phenotype are possible due to environmental influences
About 1 in 3 twins are monozygotic
Twins
DIZYGOTIC TWINS
(Fraternal Twins)
Formed with 2 separate ova & 2 separate sperm
occurs twice as often as monozygotic twins
Share half of genes, like full siblings
Can look different or very alike
Older women double-ovulate
Is it possible for fraternal twins to have different fathers?
Multiples.about.com
Assisted Reproduction Technology (ART)
techniques designed to help infertile couples conceive
and sustain a pregnancy
About 12% of U.S. couples cannot conceive
Infertility
Failure to conceive a child after a year of trying
Subfertile
Less fertile than ideal; not sterile
Woman may take drugs to cause ovulation
Donated sperm
Donor ova & wombs
In Vitro Fertilization (IVF) Involves mixing sperm w/surgically removed ova from the woman’s ovary and implanting zygote into a woman’s uterus
Less than 50% success
Slight increase of birth defects/later illnesses
Male/Female Differences
One-third of all fertility problems originate in woman; another third from man; final third from unknown causes.
Fertility decreases with age; faster decline for women
From Genotype to Phenotype
Genotype instigates body/brain formation
Phenotype is influenced since conception
Phenotype
Observable characteristics of an organism, including appearance, personality, intelligence, and all other traits
Most traits are
Polygenic
Influenced by many genes
Multifactorial
Influenced by many factors
Genes & environment
A child may have genes for musical genius, but potential is not realized & environment doesn’t support it
Epigenetics
Do genes determine everything?
Research changed perspective
Epigenetic
Epigenetics- the study of exactly how genes change in form and expression
Schizophrenia- no single gene, traits arise from a combination of genes
Gene expression depends on environment
Diseases can be delayed or facilitated, depending on certain environmental influences (drug abuse, injuries, food, love, care, etc.)
Current consensus
Genes affect every aspect of behavior
Most environment influences on children raised in the same home are not shared
Genes elicit responses that shape development
Lifelong, people choose friends and environments that encourage their genetic predispositions
Genotype and Phenotype
Alcoholism
Genes create addictive pull
Alcoholism is polygenic and culture is pivotal
Risk
Biological sex
Gender
Contexts
Ethnicity
Nature and nurture must combine to create an alcoholic
Human Genome Project
International effort project to map the complete human genetic code
Officially completed in 2001, but still ongoing
(Started in the 1980s)
100,000 20,000 genes
Many of our genes are common with other species
Crucial difference is brain size (proportion)
Dominant vs. Recessive
Alleles interact in a Dominant – Recessive pattern
One allele is dominant
One allele is recessive
Dominant = more influential & controls the gene
Ex. Dominant brown eye gene and recessive blue eye gene can result in hazel eyes
Carrier
Person with a gene that is not expressed (recessive gene)
Eye Color
Blue eyes Recessive ‘b’ allele
Brown eyes Dominant ‘B’ allele
Recessive genes
Most recessive genes are NOT harmful
However, some can be
Color blindness, allergies, diseases, learning disabilities
Especially if that recessive gene is located on the X-gene
X-Linked (mother)
Male = XY; Female = XX
Sons have more of a chance to express the recessive gene in their phenotype
20x more boys are color-blind than girls
Chromosomal & Genetic Problems
More or Fewer than 46 chromosomes
Women’s age
5 to 10% conceptions
1% of born
Abortion, miscarriage
Stillborn, or die within first few days
Chromosomal and Genetic Problems
Down syndrome
Called trisomy-21 because the person has three copies of chromosome 21
Distinct characteristics (facial shape, hearing problems, muscle weakness, intellectual dev.)
Fragile X syndrome
Caused by more than 200 repetitions of one triplet on one gene
Most common form of inherited form of inherited mental retardation
Sickle-cell trait
Offers some protection against malaria
African carriers are more likely than non-carriers to survive
Cystic fibrosis
More common among people with northern European ancestors
Carriers may have been protected against cholera
Genetic Counseling
Consultation & Testing
Recommended for the following:
Family genetic conditions
Previous stillbirths or abortions
Infertile couples
Couples of same ethnic group, esp. relatives
Women over 35 & men over 40
Controversial
