gene
- a segment of a DNA molecule that gives the instructions for making proteins
- passed from parent to offspring
- they separate each other when gamets are formed
melanin
-the pigment which contributes to the color of skin and hair
alleles
- different versions of genes
- alleles for different genes usually separate independently from one another
- if 2 or more forms/alleles of the gene for the same trait exist, some are dominant and others may be recessive
Punnett Square
- the gene combos that might result from a genetic cross
- mom on the top
- dad of the side
genetics
the study of geredity
homozygous
- both copies of the same allele for the same trait (BB, bb)
- true breeding
heterozygous
- type of gene combo of 2 different alleles for the same trait (Bb)
- aka: hybrid for particuar trait
dominant allele
- capital letter
- observed trait
- normal, funcional enzyme
recessive allele
- lower-case letter
- hidden trait
- non-funcional enzyme
genotype
-genetic makeup of an individual (allele combination)
phenotype
-observable physical and physiological characteristics of an individual
probability
- the likelihood that a particular event will occur
- predict the average outcome of a large number of events
- cannot predict the precise outcome of an individual event
- in genetics, the larger the # of offspring, the closer the resulting # will get the expected values
the principles of probability
-used to predict the outcomes of genetic crosses
F1
-1st generation of offspring
P
-parent generation
F2
-2nd generation of offspring
Gregor Mendel
- known as the father of genetics
- high school teacher, took care of the school’s garden (pea plants)
- became curious about how the plants passed on certain traits (color height…etc)
- established 3 principles…..
1. Principle of Dominance and Recessive: one trait is covered up by another trait
2. Principle of Segregation; the two alleles for a trait separate during meiosis
3. Principle of Independent Assortment: traits separate independently of one another during meiosis - performs a 2-factor cross to see if different traits would sepaarate
- exceptions= incomplete dominnce, codominance, multiple alleles , polygenetic traits
heredity
-passing of characteristics from parent to offspring
independent assortment
- genes that separate independently of one another during meiosis
- genes that segrgate independently do not influence each other’s inheritance
- 9:3:3:1 ratio in F2 generation
incomplete dominace
- when 1 allele is not completely dominant over the other
- the heterozygous phenotype is between the 2 homozygous phenotype (AA = grey is between AA= black and aa= white)
codominance
- both alleles contribute to the phenoptype
- both phenotypes contribute to the offspring’s phenotype (spots)
multiple alleles
- genes that are controlled by more then 2 alleles
- ex: a rabbit’s coat color is determined by a songle gene that has at least 4 different alleles
polygenetic traits
- traits controlled by 2 or more genes
- ex: skin color= controlled by 4 different genes; eye/hair color
Type A
-IA IA; IA i
Type B
-IB IB; IB i
Type AB
IA IB
Type 0
i i
cross fertilization
-pollen from 1 flower fertilized egg from another flower
self fertilization
-pollen fertilizes egg from the same plant
pedigree
- shows patterns of inheritance
- uses family tree and info about affected individuals…..
1. to figure out th genetic basis of a disease or trait
2. to predict thhe risk of disease in fitire offspring in a family - basic patterns of inheritance……
- autosomal, recessive
- autosomal, dominant
- sex-linked, recessive
- sex-linked, dominant (very rare)
sex-linked inheritance
- recessive
- sex linked traits are carried on the X chromosome
- nothing on the Y chromosome
- males exhibit sex-linked traits more because females will only exhibit sex linked trait if she recieves 2 allels for that 1 trait (1 one each X chromosome) and males only need 1 X chromosome, on which the trait is carried on
Y chromosome
-makes sure that half the human population is male and half is female
autosomal, recessive traits
- rare in predigree
- often skips a generation
- affects males and females equally
- hidden in heterozygous carriers
- diseases…..
1. Cystic Fibrosis (mucus clogs organs)
2. Sick Cells Anemia (irregular shaped blood cells; blood can’t carry enough oxygen)
3. Phenylketonuria (PKU)= failure of brain to develop in infancy
4. Tay-Sachs disease (infants die at an early age) - For each of these, overdominance (heterozygote superiority) has been suggested as a factor in maintaining the disease alleles at high frequency in some populations
autosomal, dominant traits
- Trait is common in the pedigree
- Trait is found in every generation
- Affected individuals transmit the trait to ~1/2 of their children (regardless of sex)
- few disease
- ex: achondroplasia (a sketelal disorder causing dwarfism)
sex-linked, recessive traits
- Trait is rare in pedigree
- Trait skips generations
- Affected fathers DO NOT pass to their sons
- males are more often affected than females
- ex: hemophilia
- ex: Glucose-6-Phosphate Dehydrogenase deficiency (hemolytic disorder causes jaundice in infants and (often fatal) sensitivity to fava beans in adults)
sex-linked, dominant traits
- Trait is common in pedigree
- Affected fathers pass to ALL of their daughters
- males and females are equally likely to be affected
- X-linked dominant diseases are extremely unusual (Often lethal (before birth) in males and only seen in females)
- ex: incontinentia pigmenti (skin lesions)
- ex: X-linked rickets (bone lesions)
Incomplete Penetrance of autosomal dominant traits
- not everyone with genotype expresses trait at all
- ex. Breast cancer genes BRCA-1 and BRCA-2 & many “genetic tendencies” for human diseases
Sex-limited expression
-trait only found in males OR females
Pedigree Analysis in real life
- dominant traits may be rare in population
- recessive traits may be common in population
- alleles may come into the pedigree from 2 sources
- mutation happens
- often traits are more complex
- affected by environment & other genes
Aneuloidies
- abnormal number of chromosomes caused by nondisjunction
- ex: down syndrome= trisomy on chromosome 21; 3 copies of a chromosome
- ex: Turner Syndrome= inherit only X chromosome in females (XO)
- ex: Klinefelter Syndrome= extra X chromosome in males (XXY)-