Mendelian Genetics Unit 4

How Genetics Began  Inheritance, or heredity  passing traits to the next generation 10.2 Mendelian Genetics Sexual Reproduction and Genetics  Mendel performed cross-pollination in pea plants.  Mendel followed various traits in the pea plants he bred. Chapter 10

 The parent generation is also known as the P generation. Sexual Reproduction and Genetics 10.2 Mendelian Genetics Chapter 10

Sexual Reproduction and Genetics  The second filial (F 2 ) generation is the offspring from the F 1 cross Mendelian Genetics Chapter 10  The offspring of this P cross are called the first filial (F 1 ) generation.

 Mendel studied seven different traits. Sexual Reproduction and Genetics  Seed or pea color  Flower color  Seed pod color  Seed shape or texture  Seed pod shape  Stem length  Flower position 10.2 Mendelian Genetics Chapter 10

Genes in Pairs Sexual Reproduction and Genetics  Allele  An alternative form of a trait 10.2 Mendelian Genetics Chapter 10  Ex. Eye color

Dominance Sexual Reproduction and Genetics  Homozygous  2 of the same alleles for a particular trait, also called pure bred or true-breeding.  Heterozygous  2 different alleles for a particular trait, also called hybrids Mendelian Genetics Chapter 10 Bb bb BB

Genotype and Phenotype Sexual Reproduction and Genetics  Genotype  allele pairs (GENES)  TT, Tt, BB, bb, Mm  Phenotype  The observable characteristic or outward expression of an allele pair (WHAT YOU SEE) 10.2 Mendelian Genetics Chapter 10 Bb

Dominant vs. Recessive Dominant  The phenotype of the organism is determined completely by one of the alleles Written with at least 1 capital letter (TT or Tt) Recessive  The other allele, has no big effect on the organism's phenotype Written with lowercase letters (bb) Example: Brown eyes is dominant and blue eyes is recessive

Mendel’s Conclusions cont’d… Ex. Tall plant (T) x short plant (t) = tall offspring (Tt) What allele was dominant?

Mendel’s Law of Segregation Sexual Reproduction and Genetics  Two alleles for each trait separate during meiosis.  During fertilization, two alleles for that trait unite Mendelian Genetics Chapter 10

Monohybrid Cross Sexual Reproduction and Genetics  A cross that involves hybrids for a single trait is called a monohybrid cross Mendelian Genetics Chapter 10

Sexual Reproduction and Genetics Dihybrid Cross  The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross.  Dihybrids are heterozygous for both traits Mendelian Genetics Chapter 10

Sexual Reproduction and Genetics Law of Independent Assortment  Random distribution of alleles occurs during gamete formation  Genes on separate chromosomes sort independently during meiosis.  Each allele combination is equally likely to occur. Law of Segregation  The two alleles for each trait separate during meiosis (ex: If a parent is Tt, then either T or t can be given to the offspring) 10.2 Mendelian Genetics Chapter 10

Sexual Reproduction and Genetics Punnett Squares  Predict the possible offspring of a cross between two known genotypes 10.2 Mendelian Genetics Chapter 10

Do this on your paper: Tt X Tt Cross: Give the genotypes, phenotypes, & percentages Go to Section: Monohybrid Crosses

Go to Section: Monohybrid Cross Answer…

Probability  the chance or percentage of chance of a trait being exhibited

Sexual Reproduction and Genetics Punnett Square— Dihybrid Cross  Four types of alleles from the male gametes and four types of alleles from the female gametes can be produced.  The resulting phenotypic ratio is 9:3:3: Mendelian Genetics Chapter 10

Genetic Recombination  The new combination of genes produced by crossing over and independent assortment 10.3 Gene Linkage and Polyploidy Sexual Reproduction and Genetics Chapter 10

Gene Linkage  The linkage of genes on a chromosome results in an exception to Mendel’s law of independent assortment because linked genes usually do not segregate independently. Sexual Reproduction and Genetics 10.3 Gene Linkage and Polyploidy Chapter 10

Sexual Reproduction and Genetics  Polyploidy is the occurrence of one or more extra sets of all chromosomes in an organism.  A triploid organism, for instance, would be designated 3n, which means that it has three complete sets of chromosomes Gene Linkage and Polyploidy Chapter 10

Genetics Disorders

Recessive

Cystic Fibrosis  Affects the mucus- producing glands, digestive enzymes, and sweat glands  Faulty ion channels

PKU phenylketonuria Recessive disorder absence of an enzyme that processes amino acid phenylalanine. Damages CNS Noticed when children begin drinking milk test for few days after birth. Treat with special diet

Albinism  Absence of melanin pigment In hair and skin  White Hair  Very pale skin  Pink, purple, or blue irises

Tay-Sachs Inability to break down lipids Causes nerve cell and mental deterioration. Most common in Jewish descent people Onset by 6 months, death by 4 years

Dominant

Huntington’s Disease Decline in nervous system functions & causes mental deterioration Ability to move deteriorates Symptoms occur age 40+

Achondroplasia small body size and limbs that are comparatively short

Sex-Linked (On X Chromosome)

Describe sex-linked alleles Sex-linked alleles: controlled by genes located on sex chromosomes Usually carried on X chromosome Since females are XX, they are usually carriers of the trait Since males are XY, they have a higher tendency for inheritance of trait

Hemophilia Failure of the blood to clot after injury

Red-Green Color-Blindness Inability to distinguish between certain colors; red- green most common

Co-Dominant

Sickle Cell Anemia Changes in hemoglobin cause red blood cells to change to a sickle shape. Low oxygen & fatigue Benefit=resistance to malaria Carriers have no symptoms, but still get benefit of resistance to malaria

Non-Disjunction

Klinefelter Syndrome Male Extra X-chromosome XXY Sterile Often cognitively delayed Some have small testes, enlarged breasts, and reduced sperm production

Turner Syndrome Only one sex chromosome (an X).sex chromosome X__ Female Short Fails to develop ovaries so become infertile

Down Syndrome 3 copies of 21 st chromosome Extra fold in eye-lid Shorter stature Cognitively delayed

Complex Inheritance and Human Heredity Pedigrees  A diagram that traces the inheritance of a particular trait through several generations 11.1 Basic Patterns of Human Inheritance Chapter 11

Interpret pedigrees Pedigrees: graphic representation of family tree Symbols identify sex, if they are carriers, if they have a certain trait, etc. Follows one trait May be used if testcross cannot be made

Pedigree Symbols

Hemophilia Pedigree

11.2 Complex Patterns of Inheritance Complex Inheritance and Human Heredity Incomplete Dominance  The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes. Chapter 11 W W WW RW WW RW

Complex Inheritance and Human Heredity Codominance  Both alleles are expressed in the heterozygous condition Complex Patterns of Inheritance Chapter 11

Complex Inheritance and Human Heredity Multiple Alleles  Blood groups in humans  ABO blood groups have three forms of alleles Complex Patterns of Inheritance Chapter 11

Human Blood Typing Human blood is classified according to the presence or absence of certain markers called antigens that are located on the surface of red blood cells. If you have the A antigen, you have type A blood and antibodies against B blood. If you have the B antigen, you have type B blood and antibodies against A blood.

What about O & AB? If you don’t have either the A or B antigen, you have type O blood. In the US, O is the most common blood type. You have antibodies against A and B. You are also a universal donor. (You can give blood to anyone) If you have both the A and B antigens, you have type AB blood and this is the rarest form of blood. No antibodies against either A or B.

Recipient’s blood type Compatible donor’s blood type A-A-, O- A+A-, A+, O-, O+ B-B-, O- B+B-, B+, O-, O+ AB-A-, B-, AB-, O- AB+A-, A+, B-, B+, AB-, AB+, O-, O+ O- O+O-, O+

Complex Inheritance and Human Heredity Coat Color of Rabbits  Multiple alleles can demonstrate a hierarchy of dominance.  In rabbits, four alleles code for coat color: C, c ch, c h, and c Complex Patterns of Inheritance Chapter 11

Complex Inheritance and Human Heredity Coat Color of Rabbits Light gray Dark gray Himalayan Albino Chinchilla 11.2 Complex Patterns of Inheritance Chapter 11

 Karyotype—micrograph in which the pairs of homologous chromosomes are arranged in decreasing size Chromosomes and Human Heredity Complex Inheritance and Human Heredity Karyotype Studies  Images of chromosomes stained during metaphase  Chromosomes are arranged in decreasing size to produce a micrograph. Chapter 11