Start-up for Tuesday, November 13, 2012 Complete the following crosses. Show your work in Punnett Squares. T = Talll R = Round t = Short r = Wrinkled A. Single Trait = If you cross a heterozygous tall plant with a short plant, what percent of the offspring do you expect to be tall? B. Two traits = What is the phenotypic ratio if you cross a pure tall round pea plant with a short wrinkled pea plant?

Genetics – Mendelian Exceptions Multiple Alleles and Sex-linked Genes Chapter 14 Section 2 Objectives: Students will A) Identify the genotypes of males compared to females B) Define sex-linked traits C) Complete punnett squares for sex-linked traits D) Predict offspring outcomes of multiple allele crosses E) Read and predict genetic outcomes from pedigrees

Exceptions to Mendel’s Laws The elegance of Mendel’s experiments was partly due to the complete consistency between his observations and hypotheses he developed. However, after Mendel’s work was rediscovered, it became clear that the simple Mendelian model did not adequately predict experimental observations in all situations.

2. Codominance – Smiley Face Lab 3. Multiple Alleles Exceptions to Mendel’s Laws Variations on Mendel 1. Incomplete Dominance 2. Codominance – Smiley Face Lab 3. Multiple Alleles 4. Polygenic Inheritance 5. Sex-linked Traits

A) Identify the genotypes of males compared to females. Human males are the heterogametic sex with two different sex chromosomes, (XY). Human females are the homogametic sex (XX). During fertilization, what is the probability that a female will result? 50%

Obj. B) Define sex-linked traits Chromosomes carry genes. Genes are located on autosomes and sex chromosomes. Genes on Autosomes – body traits Sex chromsomes- sex traits However, certain genes present in the sex chromosomes control the body traits. The characters which are controlled by such genes are called sex-linked traits and transmission of such traits from one generation to next is called sex-linked inheritance

Discovery and types of Sex linked inheritance Obj. B) Define sex-linked traits Discovery and types of Sex linked inheritance Was first discovered by Thomas H. Morgan in 1910 on Drosophila melanogaster (fruit flies). It can be classified into three types depending upon the chromosomes (X or Y) having sex linked genes. 1. X – Linked inheritance 2. Y - Linked inheritance 3. XY - Linked inheritance

Obj. B) Define sex-linked traits Certain sex-linked genes are located only on X chromosomes and their alleles are absent in Y chromosomes. These genes are called X–linked genes; Their mode of inheritance is called X-linked inheritance This pertains to the inheritance of traits which are controlled by genes located in the non-homologous part of X-chromosomes Examples: Colorblindness, Hemophilia, Duchenne Muscular Dystrophy 1. X- Linked inheritance

Color blindness – the inability to see red and green Obj. C) Complete punnett squares for sex-linked traits Color blindness – the inability to see red and green XBXB - Normal female XBXb - Carrier female XbXb - Affected female XBY - Normal Male XbY - Affected male

Sex-linked Recessive Practice Obj. C) Complete punnett squares for sex-linked traits Sex-linked Recessive Practice Trait: Color blindness Cross: Carrier female x Color Blind male XBXb x XbY Use genotypes on previous slide. Xb Y Phenotypes: 25% Carrier Females 25% Color Blind Females 25% Normal Males 25% Color Blind Males XBXb XBY XB Xb XbXb XbY

Sex-linked Recessive Example Obj. C) Complete punnett squares for sex-linked traits Sex-linked Recessive Example Trait: Color blindness Cross: Carrier female x Normal male XBXb x XBY XB Y Phenotype: 25% Normal Females 25% Carrier Females 25% Normal Males 25% Color Blind Males XBXB XBY XB Xb XBXb XbY

Obj. B) Define sex-linked traits See page 345 for a list X – Linked Recessive: 1. Affects males more than females 2. No female offspring of an affected male are affected, the trait skips generations in pedigrees. When is there an exception? Exception to this pattern occurs in the rare instance when the affected male mates with a female carrier, producing an affected female offspring. X – Linked Dominant: 1. Affected male produce all affected female offspring and no affected male offspring 2. Approximately half the offspring of affected females are affected, regardless of their sex.

Multiple Alleles It is generally accepted that a gene has two alternative forms called Alleles. Usually, one of the two alleles of a gene is dominant over the other, which is recessive e.g, Tall (TT) But in many cases, several alleles of a single gene govern the concerned trait and is known as Multiple alleles. Both prokaryotes and Eukaryotes show multiple alleles. Examples: 1. Human Blood Type 2. Fur color in rabbits and other mammals.

Multiple Alleles – Blood type Obj. D) Predict offspring outcomes of multiple allele crosses Multiple Alleles – Blood type Safe to Transfuse to A, AB B, AB AB A, B, AB, O Safe to Transfuse From A, O B, O A, B, AB, O O

Obj. D) Predict offspring outcomes of multiple allele crosses Example: homozygous male Type B (IBIB) x heterozygous female Type A (IAi) Genotype: IB IB 50% = IAIB 50% = IBi IA IAIB IBi Phenotype: 50% = AB blood type 50% = B blood type i

Obj. D) Predict offspring outcomes of multiple allele crosses Practice: male Type O (ii) x female type AB (IAIB) i IA IB Genotype: IAi IBi 50% = IAi 50% = IBi Phenotype: 50% A blood type 50% B blood type

Obj. E Read and predict genetic outcomes from pedigrees Pedigree Symbols Always read the legend Male = Female= Sexual Union= Offspring=

Obj. E) Read and predict genetic outcomes from pedigrees Shaded = color blind No shade = normal vision What does a line between a male and female indicate? What do the circles and squares beneath this mean? What are the genotypes of the following individuals: Individual #8, Generation III Individual #3, Generation II Individual #2, Generation III Sexual Union Children XbY XBXb XBXb

Hemophilia Obj. C) Complete punnett squares for sex-linked traits Hemophilia is another sex-linked trait. Hemophilia is characterized by delayed blood clotting. People with hemophilia can easily bleed to death from very minor wounds. Otherwise called “Bleeders disease”. Hemophilia is sex-linked recessive trait (hh) and the genes are located on X chromosomes. It is more common in men and rare in women.

Understanding Check – Sex-linked This disease appeared as a mutant in Queen Victoria and from her it was transmitted to her descendants. “Royal disease” = Hemophilia, Bleeder’s Disease XH XH - Normal female XH Xh - Carrier female XH Y - Normal Male Xh Y - Affected male Xh Xh - Affected female Cross a carrier female with a normal male. Identify the phenotypes.

_______ x _______ Understanding Check – Multiple Alleles Cross a heterozygous type B blood type with a AB blood type _______ x _______ Phenotype Percentages: