Chapter 12: Cell Division, Modes of Inheritance BIOL 2416 Chapter 12: Cell Division, Modes of Inheritance Chapter 11: Mendel’s Laws, Punnett Squares, Branch Diagrams, Chi Square Test

Fig. 1.22 Comparison of mitosis and meiosis in a diploid cell Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Fig. 1.22 Comparison of mitosis and meiosis in a diploid cell (continued) Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Glossary P = parental generation F1 = 1st filial generation (kids) F2 = 2nd filial generation (grandkids) Self cross = selfing = self-fertilization e.g. F1 X F1 to produce F2 Back cross = F1 x P

Glossary, cont’d: Character = heritable feature (e.g. eye color) Trait = specific version of a character (e.g. BLUE eye color) Gene = discrete unit of hereditary information = meaningful chunk of DNA that is transcribed into (m)RNA and may result in protein (e.g. the gene for eye color pigment) Allele = specific version of a gene (e.g. blue eye color allele, or brown eye color allele) Locus = specific location of gene on chromosome

Glossary, cont’d: Truebreeding = inbred to the point of homozygosity Homozygous individual = homozygote = has 2 identical alleles for a given gene (e.g. BB or bb) Heterozygous individual = heterozygote = has 2 different alleles for a given gene (e.g. Bb) Dominant allele = fully expressed in heterozygote (e.g. B) Recessive allele = masked in heterozygote (e.g. b)

Glossary, cont’d: GENotype = GENetic makeup of an individual (e.g. BB, Bb, or bb) PHenotype = PHysical characteristic of an individual (e.g. brown eyes or blue eyes); may be visible or measurable (biochemical) characteristic, or may refer to disease status.

Get in the habit…

Genotypes (help) lead to phenotypes: POSSIBLE GENOTYPES POSSIBLE PHENOTYPES BB brown eyes Bb bb blue eyes

More Glossary: Monohybrid cross = strictly speaking, a cross between 2 individuals that are heterozygous at 1 gene: Aa x Aa Dihybrid cross = strictly speaking, a cross between 2 individuals that are heterozygous at 2 genes: AaBb x AaBb

Even More Glossary: Reciprocal matings Male with 1st trait x female with 2nd trait Female with 1st trait x male with 2nd trait Test cross Individual with dominant phenotype and unknown genotype (AA or Aa?) x homozygous recessive (aa) F1 phenotypic ratios determine whether unknown genotype is AA or Aa

It is not possible to predict the genotype of an organism with a dominant phenotype. The organism must have one dominant allele, but it could be homozygous dominant or heterozygous. A test cross, breeding a homozygous recessive with dominant phenotype, but unknown geneotype, can determine the identity of the unknown allele. Fig. 14.6 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Probability Review Scale = 0 to1 (fractions or percentages) Random events occur independently of one another (separate coin tosses) Rule of Multiplication Keyword “ AND” Probability that 2 events occur simultaneously is product of individual probabilities Rule of Addition Keyword “ OR” If 2 or more independent (mutually exclusive) ways lead to Rome, add them up

Fig. 10.4 Seven character pairs in the garden pea that Mendel studied in his breeding experiments Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Gregor Mendel’s Particulate Theory of Inheritance Law of Segregation 2 alleles for a gene are packaged into separate gametes (so each gamete has ONE allele per gene) Alleles get back together after fertilization (fusion of 1 sperm + 1 egg) Law of Independent Assortment Genes on different chromosomes are transmitted independently of one another

Fig. 10.6 The F2 progeny of the cross shown in Figure 10.5 Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Fig. 10.8a Mendel’s first law, principle of segregation of Mendelian factors: Production of the F1 generation Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Fig. 10.8b Mendel’s first law, principle of segregation of Mendelian factors: Production of the F2 generation Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Fig. 10.9 Using the branch diagram approach to calculate the ratios of phenotypes in the F2 generation of the cross in Figure 10.8 Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Table 14.1 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Law of Independent Segregation: SSYY x ssyy Find genotypic ratios and phenotypic ratios in the F1 by Punnett square method Branch diagram method

Now self-cross the F1: SsYy x SsYy Find genotypic and phenotypic ratios in the F2 by Punnett square method Branch diagram method

Fig. 10.12b Derivation of F2 genotypes and 9:3:3:1 phenotypic ratio by use of the Punnett square Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Fig. 10.13 Using the branch diagram approach to calculate the F2 phenotypic ratio of the cross in Figure 10.12 Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Some Useful Numbers # of possible combinations = (# of positions) (# of choices per position)

(max) # phenotypic classes (max) # genotypic classes Ss x Ss SsYy x SsYy SsYyCc x SsYyCc (max) # gametes 21 = 2 22 = 4 23 = 8 (max) # phenotypic classes (max) # genotypic classes 31 = 3 32 = 9 33 = 27

Chi Square Test Quantifies the difference between OBSERVED and EXPECTED results Determines the likelyhood that this discrepancy is due to chance Chance is GOOD If the discrepancy is NOT due to chance, the “null hypothesis” must be REJECTED

How to Find Chi-square Value C1: List expected phenotypic classes C2: List observed numbers (o) for each class Total C3: using the expected phenotypic ratio and the total actual offspring, calculate expected numbers (e) C4: for each row, calculate d = o - e C5: for each row, calculate d2 C6: for each row, calculate d2/e Total all values in C6 to find 2 value

Chi-Square COIN TOSS C1 C2 C3 C4 C5 C6 Pheno classes o e d = o - e d2 d2 / e Heads Tails Total 100 2 =

Chi Square Probabilities Determine degrees of freedom = df = # of phenotypic classes - 1 In correct df row (see Table 11.5, pg.313), find your 2 value Move up the table to find P value If P > 0.05, the null hypothesis stands

Table 3-1

Fig. 10.16 Symbols used in human pedigree analysis Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Clues Autosomal = equal opportunity disorder (normal carriers possible) X-linked = affects males > females, if recessive (most common) Dominant = once it’s gone, it’s GONE Recessive = can skip a generation (come out of “nowhere”)

Inheritance Patterns Autosomal recessive Autosomal dominant (se)X-linked recessive (se)X-linked dominant (Y-linked) (see handout on pedigree problem strategies)

Fig. 10.17 Example of a human pedigree Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Fig. 10.19b Part of a pedigree showing the transmission of the autosomal dominant trait of woolly hair Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Human Disorder Resources http://www.ncbi.nlm.nih.gov/omim http://medgen.genetics.utah.edu/photographs.htm http://icomm.ca/geneticinfo http://www.rarediseases.org

Autosomal recessive Autosomal dominant Albinism Cystic fibrosis Tay-Sachs disease Sickle cell anemia alkaptonuria Autosomal dominant Woolly hair Achondroplasia Brachydactyly Marfan syndrome Huntington’s disease

X-linked recessive X-linked dominant Hemophilia Color blindness Duchenne’s muscular dystrophy Lesh-Nyhan syndrome X-linked dominant Faulty tooth enamel

Tests are also available to determine in utero if a child has a particular disorder. One technique, amniocentesis, can be used beginning at the 14th to 16th week of pregnancy to assess the presence of a specific disease. Fetal cells extracted from amniotic fluid are cultured and karyotyped to identify some disorders. Other disorders can be identified from chemicals in the amniotic fluids. Fig. 14.17a Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

A second technique, chorionic villus sampling (CVS) can allow faster karyotyping and can be performed as early as the eighth to tenth week of pregnancy. This technique extracts a sample of fetal tissue from the chorionic villi of the placenta. This technique is not suitable for tests requiring amniotic fluid. Fig. 14.17b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings