Problem 1: Birds and the bees Flashcards
Genotype
Genetic material inherited
Phenotype
Observable characteristics and behaviors that arise from a combination of our genotype and the environment
Chromosome
Chromosomes:
- 23 pairs similar in shape, size, and genetic function (excluding XY).
- 50/50 from both parents.
- The first 22 pairs are autosomes and are homologous (the same) and the 23rd pair is the sex chromosome (XY)
DNA
Double helix molecule connected by nucleotide
- Adenine
- Thymine
- Cytosine
- Guanine
A and T bind together, and C and G too.
Homozygous vs Heterozygous
Homozygous: equal alleles passed on from both parents.
Heterozygous: alleles differ between parents.
Conception
Fertilization > ovum > uterus > fallopian tube > fertilized by sperm > zygote
Mitosis (cell division)
- From 1 to 2, then 2 to 4, then 4 to 8, etc.
- Chromosomes split > duplication of the chromosomes (23 to 46) > they move to opposite sides > division of the cell (identical sets)
Meiosis (cell division)
- Only for sex chromosomes (germ cells)
- They produce gametes
- Duplication of the 23 chromosomes (46) > crossing-over > new unique hereditary combination
- Independent assortment: millions of different combinations.
Monozygotic vs Dyzygotic twins
Monozygotic: 100% identical, one zygote split into two identical cells.
Dygotic: Fraternal, two zygotes from two sperms, 50% identical.
- 22 out of the 23 chromosomes are the same in both females and males.
- The 23rd chromosome defines sex: Males: XY, Females: XX
Single-gene inheritance
Characteristics influenced by one pair (one allele from the mother, one from the father).
- Dominant vs recessive traits.
Co-dominance inheritance
Phenotype of the gene is a compromise between two dominant genes.
Sex-linked inheritance
- Traits located on the X sex chromosomes.
- More common in Males (females counteract the traits by having two X chromosomes unless the allele is dominant in both).
Hereditary disorders: congenital defects
- Effects present at birth but not detectable right away.
Chromosomal abnormalities: Sex chromosomes (Poly X and Poly Y)
- Poly X: 1 in 1000 female births, fertile, low IQ, normal phenotypically
- Poly-Y: 1 in 1000 male births, fertile, low sperm count, normal phenotypically.
Chromosomal abnormalities: sex chromosomes (Klinefelter’s syndrome - males)
- 1 in 1000 births, XXY, feminine traits, phenotypically male, sterile, poor cognitive abilities.
Chromosomal abnormalities: sex chromosomes (Turner’s syndrome XO)
- 1 in 2500 births (females)
- Sterile, normal IQ, one chromosome is missing.
Chromosomal abnormalities: sex chromosomes (Fragile X syndrome)
- Anomaly in the X chromosome.
- Common in males more than females, normal, prominent ears/legs, etc.
Chromosomal abnormalities: autosomes
- Down syndrome: extra part of a 21st chromosome (failed to disconnect during meiosis). Intellectually impaired, spokes problems, protruding tongue. 1 in 800 births.
Genetic abnormalities: Phenylketonuria (PKU)
1 in 10,000/20,000 births, lack of enzymes to digest food, mental retardation, etc.
Genetic abnormalities: Huntington’s disease
- Stops the brain from working over time.
- 1 in 18,000/20,000 births
- Inherited from a dominant allele
- 50% chance for children
- Symptoms: depression, poor motor skills, premature deaths, starts at 40.
Genetic abnormalities: Sickle cell anemia
1 in 500 births, abnormal red blood cells, inefficient distribution of oxygen.
The prenatal stages: conception
- Begins with fertilization.
- Once every 28 days, an ovum is released from one of the two ovaries and one of the two fallopian tubes is retracted.
- The ovum-released site, the corpus luteum, produces hormones that prepare the uterine wall for conception.
- The males’ testicles produce sperm that develop a tail that swims up the female reproductive system to the fallopian tubes where conception happens.
- Prenatal development starts with conception, lasts around 38 weeks, and can be divided into three periods:
1. The zygote period
2. The embryo period
3. The foetus period
Period of the Zygote
- The first two weeks.
- Germinal or zygote period.
- Zygote is a fertilised ovum.
- The zygote moves from the fallopian tubes to the wall of the uterus and cell division (mitosis) takes place.
- The cell division creates two parts:
1. the Blastocyst: a group of 60 to 70 cells that form a hollow, fluid-filled ball. The inner cells are called the embryonic disk, which will become the new organism.
2. The trophoblast: the outer layer of cells that provide the embryo with nutrition and protection. - Implantation also takes place (7th and 9th day): the blastocyst attaches itself to the uterine wall where it grows. Some structures form.
Structures formed during implantation: Pericarp
trophoblast multiples rapidly to form pericarp.
- protection layer
Structures formed during implantation: Amniotic fluid
The fluid protects the organism from impact, regulates temperatures, and provides a weightless environment that facilitates movement.
Structures formed during implantation: Yolk sac
- Produces blood cells until the liver, spleen, and bone marrow are mature enough to take over.
Structures formed during implantation: Chorion
- Protective membrane through which the placenta forms.
- It contains small blood cells that adhere to the uterine wall.
Structures formed during implantation: Placenta
- Ensures transfer of nutrition and oxygen to the organism and takes care of waste removal.
- Forms a membrane through which the substances can be exchanged without the blood of the mother and the child mixing.
Structures formed during implantation: Umbilical cord
- The connection between the placenta and the organism.
- It contains one large vein that delivers blood with nutrients.
- It also contains two arteries that carry away waste products.
Period of the Embryo
- Between 3rd and 8th weeks after fertilization.
- Rapid prenatal changes take place
- Groundwork for internal organs and body structures.
- The supporting systems, such as the amnion, umbilical cord, and placenta, as well as the organs continue to develop.
- The embryo is now very sensitive to changes in the environment.
- In the last half of the first month, the embryonic disk forms three layers of cells.
1. The ectoderm: the nervous system and skin
- Forms a neural tube that begins to swell to form the brain at around 3.5 weeks.
2. The mesoderm: the muscles, bones, circulatory system, and other internal organs.
3. The endoderm: the digestive system, lungs, urinary tract, and glands. - During the second month, eyes, ears, nose, jaw, and neck are formed. Arms, legs, fingers, and toes as well. The intestines grow, as well as the liver and spleen.
Period of the fetus
- From the 3rd month to birth
- Organs, muscles, and the nervous system begin to organize and become connected.
- Foetus can move.
- Genitals can be identified.
- During the second trimester, the mother can experience movement.
- Brain weight increases rapidly.
- During the third trimester, the fetus reached the age of viability.
- Fetus received antibodies from the mother.
Sensitive periods of the fetus
- Central nervous system = whole time
- Heart = 3.5-9 weeks
- Arms = 4-9 weeks
- Eyes = 4.5 onwards
- Legs = 4-9 weeks
- Teeth = 7-16 weeks
- Palate = 7-10 weeks
- External genitalia= 7.5 onwards
- Ears = 4-20 weeks
Teratogens
Environmental factors
Effects of teratogens
- During critical periods of development.
- Specific effects on specific organs.
- Genotype might counteract its effect. Vulnerability!
- The effect of one can intensify the effects of another.
- Different teratogens produce the same defect.
- The longer the exposure, the higher the intensity of the effect
- Sleeper effect: damage appears later in life.
Legal and Illegal drug effects: Caffeine
Low birth weight, poor IQ and poor motor control, high risk miscarriage
Legal and Illegal drug effects: Alcohol
- 6% of births for alcoholic mothers.
- Foetal alcohol syndrome (FAS): a lot of drinking, affects the heart, limbs, face, learning, IQ, ADHD link
Legal and Illegal drug effects: Nicotine
- ADHD link, low birth weight, genetic damage, cognitive and social development damage, and respiratory diseases.
Legal and Illegal drug effects: Marijuana
Affect growth, low birth weight, genetic damage, cognitive, and social development damage, and respiratory diseases.
Legal and Illegal drug effects: Cocaine
Physical and behavioral problems, neural damage, long-term effects
Legal and Illegal drug effects: Aspirin/diet pills
Affect fetus > low birth weight, IQ and motor control
Environmental toxins + parents’ factors
- Pollution, pesticides, radiation, mercury, food additives, cosmetics, lead, etc.
- Father’s exposure to these also affects the child (genetically).
- Age, diet, disorders.
