3.4 Inheritance The patterns that genes and the phenotypes they generate can be mapped using pedigree charts. The image show a small section of a pedigree chart that maps the inheritance of hair colour in an extended family over several generations. Analysis of pedigree charts enables us to see the nature of the inheritance; controlled by dominant or recessive alleles? linked to the sex chromosomes? controlled by multiple genes or a single gene? http://www.indiana.edu/~oso/lessons/Genetics/RealColors.html

3.4 Inheritance Essential idea: The inheritance of genes follows patterns.

WARNING: Includes a scientific scandal 3.4.U1 Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed. Mendel’s principles of inheritance Johann Gregor Mendel (1822-1884) Learn about Mendel and his work by using the weblinks Gregor Mendel: Great Minds by SciShow Because of his work with pea plants Mendel is considered the father of modern genetics. He planted 1000s of seeds per trial and carried out many trials to be sure of his results. His published work (1865) is now considered important, but at the time was ignored for 30 years. WARNING: Includes a scientific scandal Biologica: Mendel’s Peas https://youtu.be/GTiOETaZg4w?list=PLC31B0C382F9585D6 Gregor Mendel and pea plants http://biologica.concord.org/webtest1/web_labs_mendels_peas.htm https://www.dnalc.org/view/16002-Gregor-Mendel-and-pea-plants.html https://upload.wikimedia.org/wikipedia/commons/3/3d/Gregor_Mendel_oval.jpg

Definitions This image shows a pair of homologous chromosomes. Name and annotate the labeled features.

The alleles present at a gene locus maybe similar or different. 3.4.U3 The two alleles of each gene separate into different haploid daughter nuclei during meiosis. AND 3.4.U2 Gametes are haploid so contain only one allele of each gene. AND 3.4.U4 Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles. Because fertilization involves the fusion of gametes the number of chromosomes is doubled. The diploid organism also now contains two alleles for each gene. Meiosis halves the chromosomes present in gametes and reduces the number of alleles of each gene from two to one. The alleles present at a gene locus maybe similar or different. http://www.biologycorner.com/resources/diploid_life_cycle.gif

3.4.A1 Inheritance of ABO blood groups. The ABO blood type classification system uses the presence or absence of certain antigen on red blood cells to categorize blood into four types. Distinct molecules called agglutinogens (a type of antigen) are attached to the surface of red blood cells. There are two different types of agglutinogens, type "A" and type "B”. http://www.anatomybox.com/tag/erythrocytes/ http://www.ib.bioninja.com.au/_Media/abo_blood_groups_med.jpeg

Antibodies (immunoglobulins) are specific to antigens. 3.4.A1 Inheritance of ABO blood groups. Antibodies (immunoglobulins) are specific to antigens. The immune system recognizes 'foreign' antigens and produces antibodies in response - so if you are given the wrong blood type your body might react fatally as the antibodies cause the blood to clot. Blood type O is known as the universal donor, as it has no antigens against which the recipient immune system can react. Type AB is the universal recipient, as it has no antibodies which will react to AB antigens. A Nobel breakthrough in medicine. Images and more information from: http://learn.genetics.utah.edu/content/begin/traits/blood/ Blood typing game from Nobel.org: http://nobelprize.org/educational/medicine/landsteiner/readmore.html

(characteristic expressed) 3.4.A1 Inheritance of ABO blood groups. The ABO blood type is controlled by a single gene, the ABO gene. This gene has three different alleles: i O allele (no anitgen is produced) IA A allele (type “A” anitgen is produced) IB B allele (type “B” anitgen is produced) IA Allele variant Gene (lower case for ‘recessive’ alleles) Diploid cells possess two alleles therefore the possible genotype and phenotype combinations are: Genotype (allele combination) Antigen production Phenotype (characteristic expressed) ii No antigen produced Blood type O IAIA and IAi Type “A” anitgen produced Blood type A IBIB and IBi Type “B” anitgen produced Blood type B IAIB Both type “A” and “B” anitgens produced Blood type AB http://www.anatomybox.com/tag/erythrocytes/

3.4.U5 Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects. Dominant alleles have the same effect on the phenotype whether it is present in the homozygous or heterozygous state Type “A” allele present and blood type is A therefore the type “A” allele is dominant to type “O” IAi Type “O” allele present and blood type is not O therefore the type “O” allele is recessive to type “A” Recessive alleles only have an effect on the phenotype when present in the homozygous state Codominant alleles are pairs of different alleles that both affect the phenotype when present in a heterozygote IAIB Type “A” and “B” alleles are present and blood type is AB therefore type “A”and “B” alleles are codominant http://www.anatomybox.com/tag/erythrocytes/

3.4.U5 Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects. Dominant alleles have the same effect on the phenotype whether it is present in the homozygous or heterozygous state Type “A” allele present and blood type is A therefore the type “A” allele is dominant to type “O” Reality check: dominant and recessive inheritance are useful concepts for predicting the probability of inheriting certain phenotypes, especially genetic disorders. ABO Blood type is unusual as only one gene is involved in the expression of the phenotype. In most cases multiple genes contribute and/or interact to produce a trait. Whether an allele is regarded as dominant or recessive is relative and depends on the particulars of the proteins coded for. IAi Type “O” allele present and blood type is not O therefore the type “O” allele is recessive to type “A” Recessive alleles only have an effect on the phenotype when present in the homozygous state Codominant alleles are pairs of different alleles that both affect the phenotype when present in a heterozygote IAIB Type “A” and “B” alleles are present and blood type is AB therefore type “A”and “B” alleles are codominant http://www.anatomybox.com/tag/erythrocytes/

3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Explain this Mendel crossed some yellow peas with some yellow peas. Most offspring were yellow but some were green! Mendel from: http://history.nih.gov/exhibits/nirenberg/popup_htm/01_mendel.htm

3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Segregation “alleles of each gene separate into different gametes when the individual produces gametes” The yellow parent peas must be heterozygous. The yellow phenotype is expressed. Through meiosis and fertilization, some offspring peas are homozygous recessive – they express a green color. Mendel did not know about DNA, chromosomes or meiosis. Through his experiments he did work out that ‘heritable factors’ (genes) were passed on and that these could have different versions (alleles). Mendel from: http://history.nih.gov/exhibits/nirenberg/popup_htm/01_mendel.htm

Segregation F0 F1 Y y Y y Y or y Y or y 3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Segregation “alleles of each gene separate into different gametes when the individual produces gametes” F0 Key to alleles: Y = yellow y = green Genotype: Y y Y y Alleles segregate during meiosis (anaphase I) and end up in different haploid gametes. Y or y Y or y Gametes: Punnet Grid: gametes Simplified notation of using upper case for dominant and lower case for recessive is acceptable in the case of two alleles without co-dominance. F1 Genotypes: Phenotypes: Phenotype ratio: Mendel from: http://history.nih.gov/exhibits/nirenberg/popup_htm/01_mendel.htm

Monohybrid Cross F0 F1 Crossing a single trait. Y y Y y Y or y Y or y 3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Monohybrid Cross Crossing a single trait. F0 Key to alleles: Y = yellow y = green Genotype: Y y Y y Alleles segregate during meiosis (anaphase I) and end up in different haploid gametes. Fertilization results in diploid zygotes. A punnett grid can be used to deduce the potential outcomes of the cross and to calculate the expected ratio of phenotypes in the next generation (F1). Y or y Y or y Gametes: Punnet Grid: gametes F1 Genotypes: Phenotypes: Phenotype ratio: Mendel from: http://history.nih.gov/exhibits/nirenberg/popup_htm/01_mendel.htm

Monohybrid Cross F0 F1 Y y YY Yy yy Y y Y y Y or y Y or y 3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Monohybrid Cross Crossing a single trait. F0 Key to alleles: Y = yellow y = green Genotype: Y y Y y Alleles segregate during meiosis (anaphase I) and end up in different haploid gametes. Fertilisation results in diploid zygotes. A punnet grid can be used to deduce the potential outcomes of the cross and to calculate the expected ratio of phenotypes in the next generation (F1). Y or y Y or y Gametes: Punnet Grid: gametes Y y YY Yy yy F1 Genotypes: Phenotypes: Phenotype ratio: Mendel from: http://history.nih.gov/exhibits/nirenberg/popup_htm/01_mendel.htm

Monohybrid Cross F0 F1 Y y YY Yy yy Y y Y y Y or y Y or y 3 : 1 3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Monohybrid Cross Crossing a single trait. F0 Key to alleles: Y = yellow y = green Genotype: Y y Y y Alleles segregate during meiosis (anaphase I) and end up in different haploid gametes. Fertilisation results in diploid zygotes. A punnet grid can be used to deduce the potential outcomes of the cross and to calculate the expected ratio of phenotypes in the next generation (F1). Ratios are written in the simplest mathematical form. Y or y Y or y Gametes: Punnet Grid: gametes Y y YY Yy yy F1 Genotypes: YY Yy Yy yy Phenotypes: Phenotype ratio: 3 : 1 Mendel from: http://history.nih.gov/exhibits/nirenberg/popup_htm/01_mendel.htm

3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Monohybrid Cross What is the expected ratio of phenotypes in this monohybrid cross? F0 Key to alleles: Y = yellow y = green Phenotype: Genotype: Homozygous recessive Homozygous recessive Punnet Grid: gametes F1 Genotypes: Phenotypes: Phenotype ratio:

Monohybrid Cross F0 F1 y yy y y y y All green 3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Monohybrid Cross What is the expected ratio of phenotypes in this monohybrid cross? F0 Key to alleles: Y = yellow y = green Phenotype: Genotype: y y y y Homozygous recessive Homozygous recessive Punnet Grid: gametes y yy yy yy yy yy F1 Genotypes: Phenotypes: Phenotype ratio: All green

3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Monohybrid Cross What is the expected ratio of phenotypes in this monohybrid cross? F0 Key to alleles: Y = yellow y = green Phenotype: Genotype: Homozygous recessive Heterozygous Punnet Grid: gametes F1 Genotypes: Phenotypes: Phenotype ratio:

Monohybrid Cross F0 F1 Y y Yy yy y y Y y 1 : 1 3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Monohybrid Cross What is the expected ratio of phenotypes in this monohybrid cross? F0 Key to alleles: Y = yellow y = green Phenotype: Genotype: y y Y y Homozygous recessive Heterozygous Punnet Grid: gametes Y y Yy yy F1 Genotypes: Yy Yy yy yy Phenotypes: Phenotype ratio: 1 : 1

3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Monohybrid Cross What is the expected ratio of phenotypes in this monohybrid cross? F0 Key to alleles: Y = yellow y = green Phenotype: Genotype: Homozygous dominant Heterozygous Punnet Grid: gametes F1 Genotypes: Phenotypes: Phenotype ratio:

Monohybrid Cross F0 F1 Y y YY Yy Y Y Y y All yellow 3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Monohybrid Cross What is the expected ratio of phenotypes in this monohybrid cross? F0 Key to alleles: Y = yellow y = green Phenotype: Genotype: Y Y Y y Homozygous dominant Heterozygous Punnet Grid: gametes Y y YY Yy F1 Genotypes: YY YY Yy Yy Phenotypes: Phenotype ratio: All yellow

Steps to figuring out Monohybrid Crosses: 3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Steps to figuring out Monohybrid Crosses: Write down all information given Write down phenotypes & genotypes of parents Figure out gametes Draw punnett grid & fill in Determine the genotypic and phenotypic ratio for offspring

3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Practice Problem: In guinea pigs, black fur is dominant to white fur. Cross a heterozygous black guinea pig with a white guinea pig. Give the genotypes and phenotypes of the offspring. Black is dominant to white. Solution: Bb (Black) x bb (white) Genotypic ratio: Phenotypic ratio: *Do on board

Ratios for a Monohybrid Cross: 3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Ratios for a Monohybrid Cross: Anytime you cross 2 heterozygotes you always get: Genotypic ratio = 1 AA: 2 Aa: 1 aa Phenotypic ratio = 3 dominant: 1 recessive Anytime you cross a homozygote with a heterozygote you get: Genotypic ratio = 1 homozygous: 1 heterozygote These ratios can also be expressed as percentages: 3:1  75% tall; 25% short 1:2:1  25% TT; 50%Tt; 25% tt