Genetics and Heredity Flashcards
Human life begins
with the union of the mother’s egg cell with the father’s sperm cell
Egg cells (4 facts)
- -Once every 28 days an egg cell is released
- -All women’s ova are present at birth (maybe a million)
- -Only 400 will mature and be released between puberty and menopause
- -Ovum is the largest cell in the body
Sperm cells (2 facts)
- -Males produce billions of sperm per month, (200-300 million every 3-4 days), from puberty until death
- -Sperm one of the smallest cells in the body
Two types of cells
- -Body cells, or somatic: contain 23 pair of rod-like structures, which are the chromosomes
- -Sex cells (ova & sperm): contain 23 (versus 23 pair) of chromosomes each
Of the 23 chromosomes in each ova or sperm
One chromosome in labeled the sex chromosome and determines the sex of the offspring
Father produces 2 kinds of sperm
X & Y
X sperm are large and stronger
Y sperm are smaller and weaker, but faster
XX =
Female
XY =
Male
Each body cell of 46 chromosomes contains (genes)
Roughly 30,000 genes (units of heredity), includes: –skin pigmentation
- -eye color
- -Some personality traits (shyness, activity level)
- -To some extent, intelligence
Genotype
person’s hereditary makeup
- -Your actual genetic makeup
- -All genes inherited from your parents
- -Fixed at conception
Phenotype
Physical, behavioral, and psychological features that result from the interaction between one’s gene’s and the environment
- -what we see
- -Manifested characteristics
- -Not fixed - interaction between between the genotype and the environment as one develops
Examples of dominant phenotypes
Curly hair, normal hair, dark hair, thick lips, cheek dimples, normal hearing, normal vision, farsightedness, normal color vision, Type A blood, Type B blood, Rh-positive blood
Examples of recessive phenotypes
Straight hair, pattern baldness (men), blond hair, thin lips, no dimples, some types of deafness, nearsightedness, red-green color blindness, Type O blood, Rh-negative blood
Genes & Diseases - basic info
- -Genes are sometimes responsible for certain diseases & defects
- -In most cases, these disorders are linked to recessive rather than dominant genes
- -If a person has a dominant gene for a disease, it will be manifested in the carrier
- -And individual may be a carrier of a single recessive gene for an abnormality and not know it. It will only show up in offspring if both parents are carriers and pass it on.
Huntington’s Chorea
- -Fatal disease that is a progressive degeneration of the nervous system.
- -Associated with a dominant gene.
- -Doesn’t manifest itself until one is 30-40 (maybe 50) years of age
Sickle-Cell Anemia
- -Linked to recessive gene
- -Carried primarily by African-Americans
- -10% carry the gene
- -Individuals with one dominant and one recessive allele have sickle-cell trait. In most situations, they are fine, but if they suffer a serious shortage of oxygen, they suffer a temporary, relatively mild form of the disease.
Incomplete dominance
Situation in which one allele does not dominate another completely
What is an allele
variations of genes
There are different forms of genes known as alleles
-If alleles in the pair of chromosomes are the same, they are homozygous
–If alleles in a pair of chromosomes differ, they are hetrozygous
PKU
- -Liver enzyme missing that prevents certain foods from breaking down properly
- -Undetected can lead to MR and brain seizures
- -Can be detected in newborns (blood or urine test) and avoided by special diet
Tay-Sacks disease
- -Enzyme disorder where the brain is unable to break down certain fatty substances
- -1st symptoms occur at 6 months
- -Child generally dies before ages 3-5
- -Can be detected but not prevented
Downs Syndrome - Trisomy 21
- -Chromosomal disorder
- -Occurs in 1 of every 680 births
- -Extra chromosome on chromosome 21 (3 instead of normal pair of 2)
- -Risk increases with the parents’ age, especially the mother
- -Mother in late 20s - 1 in 1000 births
- -Mother in her early 40s - 1 in 50 births
Turner Syndrome
- -Associated with the Sex Chromosome
- -1 in 2500 - 5000 females is missing an X sex chromosome (XO)
- -Most are spontaneously aborted (90%)
- -Survivors have underdeveloped sex characteristics
- -Treatable with estrogen
- -Females are sterile
Klinefelters Syndrome
- -Associated with sex chromosome
- -Presence of extra X in males (XXY)
- 1 in 500
- -Small, underdeveloped testicles
- -Some breast development
- -High-pitched voice
- -Little facial hair
- -many infertile
- -Treatable with testosterone
XYY Syndrome
- -“Super males”
- -1 in 1000
- -Taller
- -Lower than average intelligence
- -Tend to be more aggressive (not definitive)
Fragile X Syndrome
- -The X sex chromosome is abnormally compressed or broken
- -More common in males
- -Results in mental retardation
- -No symptoms until puberty
XXX Syndrome
- -Occurs in about 1 in 1000 newborn girls
- -5-10 girls with Triple X Syndrome are born in the US every day
- -May be taller than average, but typically causes no unusual physical features
- -Most females with Triple X Syndrome have normal sexual development and are able to conceive children.
- -May have delayed motor and language
- -May have seizure or kidney abnormalities
Genetics and Autism
There is a genetic flaw linked to autism, study published in New England Journal of Medicine in 2008
