Genetics

1. Chapter 2 Science 30 Genetics

2. What is genetics? • Genetics is the study of how traits are passed from parent to offspring • Nucleus of cells contain genetic material organized into chromosomes. • Chromosomes carry genes, units of hereditary. • Each chromosome contains many different genes. • Humans have 23 pairs of chromosomes (46 total). • 1 set from each parent.

4. Chromosomes • Long, thin coiled strands of DNA • Seen during cell division. • X shape is created when copies attach at one point (centromere). BrainPop - DNA

5. Genes • A segment of DNA that codes for a specific protein. • The order of the bases codes for a specific trait (e.g.. Tongue rolling). • Some genes are dominant and some are recessive. Free ear lobe a.) is dominant to attached ear lobe b.).

6. Role of proteins • Each gene makes a protein…these are used for/as: • Enzymes (amylase- digestion). • Structural (Keratin/ collagen). • Transport ( cell membranes). • Hormones (insulin). • Defense (antibodies). • Energy (Casein). • Muscle contraction (Actin and myosin). BrainPop - RNA

8. Human karyotype • All 23 chromosomes matched to their pair is a called a karyotype. • 3 features are used to identify pairs: • Length of chromosome (longest = #1) • Pattern of dark bands on chromosome. • Position of centre connection (centromere). • The last 2 chromosomes are the sex chromosomes: • XX = female. • XY= male

10. Amniocentesis • Prenatal test done to determine karyotype fetus • Taken during week 15 – 16 of pregnancy • Used to diagnose genetic abnormalities such as a trisomy (3 copies of a single chromosome)

11. Trisomy • Trisomy 21 – Down Syndrome • Trisomy 18 – Edward’s Syndrome • Trisomy 13 – Patau Syndrome • XXY – Klinefelter Syndrome

12. Down Syndrome (21) • Results in: • Delayed physical growth • Lowered cognitive ability • Congenital heart disease in 50% of individuals • Most common autosomal trisomy

13. Edward’s Syndrome (18) • Results in : • Kidney and heart malformations • Developmental delays • Cleft lip and palate • Protruding intestines • Second most common autosomal trisomy

14. Patau Syndrome (13) • Results in: • Developmental delays • Heart and kidney defects • Polydactalism • Cleft lip and palate • Malformed genitalia

15. Klinefelter Syndrome (XXY) • Small children may have reduced muscular development and strength • Symptoms may not be visible until the on-set of puberty • Individuals may have breast development due to reduced levels of testosterone.

16. Chromosome Replication • The 2 ways that an exact copy of the DNA from the chromosome is created are: • Mitosis: • occurs in somatic/ autosomal (body cells) • Asexual reproduction • Meiosis: • Occurs in germ cells (in ovaries and testes) • Produces gametes (egg and sperm) for sexual reproduction

17. Mitosis • Body cells (autosomal cells) divide by replicating all the parts and dividing into 2 identical cells • 1 parent cell = 2 identical daughter cells • A copy of the DNA must be made before replication; each strand replicates and attaches at a centre point (centromere). • Parent cell is diploid; 2n(2 copies of each chromosome • Daughter cells are diploid; 2n (2 copies of each chromosome)

18. Summary of Mitosis: BrainPop - Mitosis

19. Meiosis • Occurs in germ cells to produce gametes (egg or sperm) • Germ cell replicates DNA and divides twice • 1 parent cell = 4 sex cells • Parent cell is diploid; 2n (2 copies of each chromosome) • Sex cell is haploid; 1n (1 copy of each chromosome)

20. Summary of Meiosis:

22. Fertilization • The sperm and the egg (gametes) are each haploid, the fertilized egg (zygote) is diploid and can reproduce through mitosis. • This increases variation and allows for more than 70 trillion gene combinations. • Crossing over improves the variation possible in the gametes; explains why 2 siblings look so different. BrainPop - Gender Determination

24. Inheritance ideas • Charles Darwin had produced the theory of evolution through natural selection during the 19th century • Darwin understood that traits were passed from parent to offspring but did not understand how…

25. Gregor Mendel • The “father of genetics” • (1822-1884) Gregor Mendel’s work with garden peas provided missing piece in theory of evolution by natural selection. • Noticed that traits were not blended but instead one was dominant. BrainPop - Heredity

26. Crosspollination • Transferring pollen between genetically different plants. • Mendel discovered that some traits were easy to recognize and studied these.

27. 1st Generation Breeding 2nd Generation Breeding

28. Mendel’s laws • Inherited characteristics are controlled by genes that occur in pairs; each gamete receives 1 gene (law of segregation). • Principal of dominance- 1 gene masks the effect of the other. • Dominant trait = capital letter • Recessive trait = lowercase letter

29. Individuals randomly inherit genes from parents. Independent inheritance of traits to offspring- not linked to other traits.

30. Inheritance • Inherited traits: • passed from parent to offspring via genes • example: blood type, eye color, hair color • Acquired traits: • due to environment; not genes • cannot be passed from parent to offspring • example: scars

31. Alleles • A form of a gene responsible for a trait (e.g. Tongue rolling). • Individuals have 2 alleles for every trait located on chromosomes. • When the chromosomes separate during meiosis, 1 allele is passed to each gamete.

32. Dominance Theory • Alleles can be dominant or recessive. • A dominant allele masks a recessive allele • Recessive traits are coded only when an offspring receives 2 recessive alleles.

33. Genetic terms • Homozygous: two identical copies of an allele • can be homozygous dominant or recessive • (ie. RR or Rr) • Heterozygous: two different copies of an allele • (ie. Rr) • Genotype: the genes that an individual has • (ie. the rose plant has the genotype Rr) • Phenotype: how the gene is expressed; the observed trait • (ie. the rose has red flowers)

34. Punnett Squares • If alleles are known, a Punnett square is used to predict the probability of offspring genotype. • To Draw a Punnett Square: • Draw a square and label each row with alleles of the gamete. • Fill in the squares with the genotype. • Determine the probability of the offspring with each genotype; expressed as a percentage (%)

37. Codominance • Not all traits are controlled by one gene or have only two alleles for a gene • Codominance is a condition where both allele products are expressed at the same time

38. Codominance - Blood Types • Controlled by 3 alleles: • A, B, O. • Produce 4 genotypes: • A, AB, B, O. • O is recessive; individual needs to be homozygous for type. • A and B are codominant; both can be expressed at the same time.

39. Codominance - Blood Types BrainPop – Blood Type

40. Who’s the daddy? The Maury Povich Show needs your help in determining the father of a new born baby. The blood type of the mother, baby and potential fathers are known. • Based on the information in the table, which could not be the father of the baby? Use a Punnett square to justify your answer. • Explain why blood type information cannot be used to determine who the father of the baby is, and only who the father of the baby is not.

41. Gender determination • Mother has only X chromosomes; all eggs have an X chromosome. • Father determines the gender of the baby; 50% chance for either gender.

42. Sex linked traits • Autosomal trait: • controlled by genes on chromosomes 1-22 • Sex-linked trait: • controlled by genes located on sex chromosomes (X or Y). • ie. colorblindness, hemophilia

43. Deoxyribonucleic Acid (DNA) • DNA: • double helix structure (twisted ladder) • Composed of nucleotides: • sugar and phosphate “backbone” • bases (adenine, thymine, cytosine, guanine)

44. Nitrogen Bases • There are 4 Nitrogen bases: • adenine (A) • thymine (T) • cytosine (C) • guanine (G) • Hydrogen bonds hold bases together; base pair • Only certain bases bond together: • A and T • C and G

45. Base Pairs Bonding • DNA molecule has 1 base strand and 1 complementary base strand. • adenine pairs with thymine • cytosine pairs with guanine • 2 strands form the ladder, with the bonded pairs becoming the ‘rungs’. • What is the complementary strand to: • ATTGCCGATGC

47. DNA Replication • DNA is only molecule known to duplicate itself (replication) • DNA must replicate before 1 cell can divide into 2 cells • During replication: • weak H bonds are broken • 2 edges of the ladder "unzip" • each strand acts as a template to which free floating nucleotides in cell can attach • new DNA strand is made 47

49. The Genetic Code and Protein Synthesis • mRNA copies the DNA sequence and transports it to ribosomes outside nucleus for protein synthesis • Order of bases in a gene code for a specific protein: • order of bases code for the production of amino acids • amino acids are assembled in ribosomes to make proteins • 3 bases (DNA triplet/ codon) codes for a specific amino acid • 64 possible DNA triplets/ codons code for 20 amino acids.

50. mRNA takes DNA to ribosome and tells them what protein to make. • To start or stop amino acid assembly, a specific codon is used: • Start = Initiator codon (ATG) • Stop = terminator codon (TAA, TAG, TGA)