- Slides: 20
Applied Biology Genetics Notes
Genetics Introduction • Genetics is the study of heredity • Heredity explains why you look like your parents or siblings (similar traits) • Traits (ex. Color, shape) are inherited or passed down to offspring in genetic crosses
Essential Vocabulary! • Gene – parts of DNA that control traits • Gregor Mendel – “Father of Genetics”, studied inheritable information & performed plant-cross experiments
Dominant vs Recessive Dominant gene – trait ALWAYS shows itself Recessive gene – trait hidden when dominant gene is present Allele – forms of a particular gene (we use caps & lower case letters) (R = round and r = wrinkled……. but both code for shape)
Homozygous vs. Heterozygous • Homozygous – 2 of same allele for a trait (RR or rr) • Heterozygous – 2 different alleles for a trait (Rr)
Phenotype vs. Genotype • Phenotype – physical observable trait (shape, color ect. ) • Genotype – genetic make-up, combination of alleles (RR, Rr, rr) Phenotype (purple)
Solving Genetics Problems 1. Designate letters for traits (R=Round, r=wrinkled) 2. Determine parent alleles 3. Set up Punnett square 4. Fill – in Squares 5. Determine possible offspring genotypes & Phenotypes
Practice Problem Black hair (B) is dominant over brown hair (b). A man heterozygous for black hair and a woman with brown hair have children. What are the genotypes and phenotypes of their offspring? Step #1 B = black Step #2 Dad = Step #3 (punnett square) Step #4 (fill-in offspring squares) Step #5 (Genotypes & phenotypes) b = brown Mom =
Blood Typing Genetics (Codominance & Multiple Alleles) • In simple genetics…there are usually 2 alleles – 1 dominant (R) & 1 recessive (r) • In Codominance…neither allele is dominant over the other! • Since they are COdominant…they both show up in the heterozygous phenotype!
Blood Typing Genetics (cont. ) • Usually in simple genetics problems we have: – 1 Dominant Allele – 1 Recessive Allele R or r • In Blood typing, we have: – 2 Dominant Alleles = A & B – 1 Recessive Allele = o EXAMPLE: Blood Types!
Blood Typing - Codominance • In humans, there are 4 possible blood types: A, B, AB, and O. • Type O individuals are considered to be the “universal donors”, whereas type AB individuals are said to be “universal recipients”!
Blood Type Genotypes Type A Blood – AA is homozygous – Ao is heterozygous Type B Blood – BB is homozygous – Bo is heterozygous Type AB Blood – AB (this is the co-dominant blood type!) Type O Blood – oo (only 1 way to have Type O blood because o is recessive!)
Blood Typing – Practice Problem A man heterozygous for Type A blood and woman homozygous for Type B blood have children. What are the possible genotypes and phenotypes of their offspring?
Practice Problem #2 Two babies are ready to go home from the hospital…Which baby belongs to which parents? • Here’s what you know about the babies: – Baby A bas blood type A – Baby B has blood type O Parents #1 - Father (Homozygous Type A) & Mother (Type O) Parents #2 - Father & Mother (Heterozygous A)
Sex Linkage – Hemophilia Some traits are carried on the X chromosome!! Hemophilia is the most wellknown sex-linked disease! Males = X Y Females = X X
Hemophilia Lacking the ability for blood to clot…can’t stop bleeding Possible Genotypes: Hemophilic Male Genotype = X Y Hemophilic Female = X X Normal Male Genotype = X Y Normal Female Genotypes = X X (CARRIER)
Practice Sex Linkage (Hemophilia) Problem A man with hemophilia and a normal women (but carrier for hemophilia) have a child. What are the possible genotypes and phenotypes of their offspring? Man = X Y Woman = X X Offspring Genotypes: Offspring Phenotypes:
Human Genetics Karyotype - the complete set of chromosomes in a species. Can show chromosomal disorders such as: 1. Down Syndrome (Trisomy 21) 2. Turner Syndrome (X missing pieces) 3. Klinefelter Syndrome (XXY) Chromosomal Disorders occur due to NONDISJUNCTION – error in meiosis where chromosomes don’t separate correctly during anaphase!
Human Genetics - Pedigrees