Mendelian Patterns of Inheritance Chapter 11 Mendelian Patterns of Inheritance 1

Early Ideas about Heredity People knew that sperm and eggs transmitted information about traits Blending theory Problem: Would expect variation to disappear Variation in traits persists 2

Gregor Mendel 1st to apply mathematics to biology Careful, delibrate Well prepared 3

Garden Pea Easy to grow Self/cross pollination Many varieties Used discrete traits, easily observed

Tracking Generations Parental generation P mates to produce First-generation offspring F1 mate to produce Second-generation offspring F2 5

Experimental intercross between Monohybrid Crosses Experimental intercross between two F1 heterozygotes AA X aa Aa (F1 monohybrids) Aa X Aa ? 6

Mendel’s Monohybrid Cross Results 5,474 round 1,850 wrinkled 6,022 yellow 2,001 green 882 inflated 299 wrinkled 428 green 152 yellow F2 plants showed dominant-to-recessive ratio that averaged 3:1 705 purple 224 white 651 long stem 207 at tip 787 tall 277 dwarf Fig. 11-6, p. 172 7

Genes Allele Units of information about specific traits Passed from parents to offspring Each has a specific location (locus) on a chromosome Different molecular forms of a gene Arise by mutation Dominant allele masks a recessive allele that is paired with it 8

Allele Combinations Homozygous Heterozygous having two identical alleles at a locus AA or aa true-breeding Heterozygous having two different alleles at a locus Aa hybrids 9

Genotype & Phenotype Genotype refers to particular genes an individual carries Phenotype refers to an individual’s observable traits Cannot always determine genotype by observing phenotype 10

Check Progress B = black, b= white If a heterozygous rabbit reproduces with one of its own kind, what phenotypic ratio do you expect among the offspring? If there are 120 rabbits, how many expected to be white?

11.2 Mendel’s laws Each indv has 2 alleles for each trait Law of Segregation Law of Independent Assortment Each indv has 2 alleles for each trait Alleles separate when gametes form Gametes have 1 allele for each trait Fertilization gives new indv 2 alleles Each pair of alleles assorts indepently All possible combo of alleles can occur Applies to alleles on diff c-somes Expected ratio 9:3:3:1

Dihybrid Cross Experimental cross between individuals that are homozygous for different versions of two traits 13

In fruit flies, L = long wings and l = short wings; G = gray body and g = black body. List all possible gametes for a heterozygote

Dihybrid Cross: F1 Results purple flowers, tall white flowers, dwarf TRUE- BREEDING PARENTS: AABB x aabb GAMETES: AB AB ab ab AaBb F1 HYBRID OFFSPRING: All purple-flowered, tall 15

1/4 1/4 1/4 1/4 AB Ab aB ab 1/4 AB 1/4 Ab aB 1/4 ab meiosis, gamete formation AB Ab aB ab 1/4 1/16 1/16 1/16 1/16 AB AABB AABb AaBB AaBb 1/4 Ab 1/16 1/16 1/16 1/16 AABb AAbb AaBb Aabb 1/16 1/16 1/16 1/16 AaBB AaBb aaBB aaBb aB 1/4 1/16 1/16 1/16 1/16 AaBb Aabb aaBb aabb ab Fig. 11-9b, p.175 16

Laws and Meiosis Doesn’t matter which way the homologous pair faces during metaphase I (2nd law) Metaphase II cell has one chromosome (1st law) Gametes can have all possible combinations of alleles (both laws) OR

See p. 196

Test Cross Individual that shows dominant phenotype is crossed with individual with recessive phenotype Examining offspring allows you to determine the genotype of the dominant individual 19

Autosomal Recessive Inheritance Patterns If parents are both heterozygous, child will have a 25% chance of being affected Fig. 12-10b, p. 191 21

Examples Methemoglobinemia Cystic Fibrous Niemann-Pick

Autosomal Dominant Inheritance Trait typically appears in every generation Fig. 12-10a, p. 190 23

Achondroplasia Autosomal dominant allele In homozygous form usually leads to stillbirth Heterozygotes display a type of dwarfism Have short arms and legs relative to other body parts 24

Huntington Disorder Autosomal dominant allele Causes involuntary movements, nervous system deterioration, death Symptoms don’t usually show up until person is past age 30 People often pass allele on before they know they have it 25

ABO Blood Type Range of genotypes: IAIA IBIB or or IAi IAIB IBi ii Fig. 11-10a, p.176 26

Codominance: ABO Blood Types Gene that controls ABO type codes for enzyme that dictates structure of a glycolipid on blood cells Two alleles (IA and IB) are codominant when paired Third allele (i) is recessive to others Also known as Multiple Alleles 27

Incomplete Dominance Incomplete Dominance X Homozygous parent Intermediate phenotype Familial hypercholesterolemia CF heterozygous Incomplete pentrance polydactyly All F1 are heterozygous X F2 shows three phenotypes in 1:2:1 ratio 28

The allele for albinism (c) is recessive to allele for normal pignmentation (C). A normally pigmented woman whose father is an albino marries a man whose parents are normal. They have 3 children, 2 normal and 1 albino. Give the genotypes for each person.

In garden peas, one pair of alleles controls the height of the plant and a second pair of alleles controls flower. The allele for tall (D) is dominant to allele for dwarf (d), and the allele for purple (P) is dominant to the allele for white (p). A homozygous tall purple plant is crossed with a dwarf white plant. What is the appearance of F1 and F2?

Epistasis Interaction between the products of gene pairs Common among genes for hair color in mammals 31

Examples Antocyanin pigments Lab coat color Eye color humans Start molecule colorless Intermediate colorless  Purple Lab coat color Start molecule melanin  deposition Eye color humans Blue 1  Blue 2  Green  Brown

Coat Color in Retrievers BBEE X bbee F1 puppies are all BbEe F2 puppies BE Be bE be BE BBEE BBEe BbEE BbEe black Be BBEe BBee BbEe Bbee brown bE BbEE BbEe bbEE bbEe yellow be BbEe Bbee bbEe bbee 33

Pleiotropy Alleles at a single locus may have effects on two or more traits Marfan syndrome - Mutation in gene for fibrillin affects skeleton, cardiovascular system, lungs, eyes, and skin 34

Polygenic A more or less continuous range of small differences in a given trait among individuals The greater the number of genes and environmental factors that affect a trait, the more continuous the variation in versions of that trait 35

Continuous Variation Variation in human eye color Eye color Calculator Fig. 11-18, p.180 36

Temperature Effects on Phenotype Rabbit is homozygous for an allele that specifies a heat- sensitive version of an enzyme in melanin-producing pathway Melanin is produced in cooler areas of body Figure 11.16 Page 179 37

Environmental Effects on Plant Phenotype Hydrangea macrophylla Action of gene responsible for floral color is influenced by soil acidity Flower color ranges from pink to blue 38

Elevation and the yarrow Fig. 11-17b, p.179 39

X-Linked Recessive Inheritance Males show disorder more than females Son cannot inherit disorder from his father Fig. 12-10, p.194 40 40

Thomas Morgan 1900’s Red female x white male = all red F2 = 3 red: 1 white male Supported chromosome theory of inheritance Males = hemizygous 41 41

Fig. 12-9, p.193 42 42

Examples of X-Linked Traits Color blindness Hemophilia Menkes syndrome Muscular Dystrophy Adrenoleukodystrohy (ALD) 43 43

Color Blindness Fig. 12-12, p.195 44 44

Color Blindness Fig. 12-12, p.195 45 45

1 XrXr 2 XRY 3 XRY 4 XRXr 5XrY 6 XRXr 7 XrY 8 XrXr 9 XrY 10XRX 11 XRY 12 XRX 13 XrY 14 XrXr 15 XrY

Hemophilia Fig. 12-11, p.194 47