KEY CONCEPT Genes encode proteins that produce a diverse range of traits.

The same gene can have many versions. A gene is a piece of DNA that directs a cell to make a certain protein. Each gene has a locus, a specific location on a pair of homologous chromosomes.

Each parent donates one allele for every gene. An allele is any alternative form of a gene occurring at a specific locus on a chromosome. Each parent donates one allele for every gene. Homozygous pairs describes two alleles that are the same. Heterozygous pairs describes two alleles that are different. Mom Dad

Genes influence the development of traits. A genotype refers to the makeup of a specific set of genes. A phenotype is the physical expression of a trait.

Alleles can be represented using letters. Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters. Dominant genes are expressed as a phenotype even when only one allele is dominant . Recessive genes are expressed as a phenotype when two copies of the recessive allele are present.

Both homozygous dominant (SS) and heterozygous (Ss) genotypes yield a dominant phenotype. But only recessive genotypes (ss) yield a recessive phenotype(blue eyes)

Many traits are determined by dominant and recessive alleles Look at your seat partner determine which types of traits he or she has write them down: attached or unattached earlobe cleft chin or round Chin straight hairline or a widow’s peak hairline dimples or no dimples rolled tongue or clover tongue - Can we determine which traits are dominant and which traits are recessive?

Punnett Squares Punnett squares can help us mathematically determine which traits are dominant and which traits are recessive.

Genotypes of parents Possible genotypes of offspring How does it look like? Genotypes of parents Possible genotypes of offspring

Step 1: Figure out the parent’s genotypes and fill it in the axes. How do you fill it out? Step 1: Figure out the parent’s genotypes and fill it in the axes. Step 2: Fill in the alleles down each column and row

d D Dd D = non-diabetic d = diabetic So what? Why do we need it? We can use it to predict the probability our child’s genotype and phenotype Probability  ratios D = non-diabetic d = diabetic There is 0 chance that the children will be diabetic d D Dd

COUNT how many times each genotype occurs. How do we find the ratio? COUNT how many times each genotype occurs. BB = 1 homozygous dominant Bb = 2 Heterozygous Dominant bb = 1 Homozygous recessive So the ratio is 1:2:1 What about probabilities?

A green pea plant (Gg) is crossed with a yellow pea plant (gg). Question #1: Create the Punnett Square determine the ratios, and calculate probabilities A green pea plant (Gg) is crossed with a yellow pea plant (gg). Ratio: _______ : ________ : ________ Probability of green pea plant: Probability of yellow pea plant:

Question #2: Create the Punnett Square and determine the ratios A tall plant that is homozygous dominant (TT) is crossed with a tall plant that is heterozygous (Tt). Ratio: _______ : ________ : ________ Probability of tall plant Probability of short plant:

Sometimes you will be asked to examine two traits. Dihybrid Crosses Sometimes you will be asked to examine two traits. Dihybrid crosses examine the inheritance of two different traits that are sometimes linked together

Dihybrid Cross – How do you fill it out? Step 1: Figure out the parent’s genotypes: RYry x ryry Step 2: Figure out possible gametes Use FOIL method to determine what letters go in each box Step 3: Fill in the corresponding columns and rows

Calculating Ratios and Probability To start: count the phenotypes Probability of round yellow: 9/16 Probability of round green: 3/16 Probability of wrinkled: yellow 3/16 Probability of wrinkled green: 1/16

Incomplete dominance Sometimes traits are neither one or the other, this is called incomplete dominance

Incomplete dominance

Co- dominance Occurs when alternative alleles are present in the genotype and fully observed in the phenotype. Instead of one or the other, or something in between, both phenotypes are expressed.

Genetic Inheritance The genetics of Disease, Sex-linkage and the Law of Segregation

I = dominant i = recessive Genotype Phenotype (blood group) Co- dominance I = dominant i = recessive Genotype Phenotype (blood group) IA IA or IAi A IB IB, or IBi B IAIB AB ii O

Autosomal Dominant Inheritance Dominant gene located on 1 of the autosomes Letters used are upper case (BB or Bb) Affected individuals have to carry at least 1 dominant gene (heterozygous or homozygous) Passed onto males and females Every person affected must have at least 1 parent with the trait Does not skip generations E.g. Huntington’s disease, Marfan syndrome

Huntington's disease is a brain disorder Huntington's disease is a brain disorder. It affects the person's ability to think, talk, and move. It affects the part of the brain that controls the thinking, emotion, and movement.  The average life expectancy of a person who was just diagnosed is around 15 years.

Marfan syndrome is an inherited disorder of the connective tissue that causes abnormalities of a child's eyes, cardiovascular system, & musculoskeletal system.

Autosomal Recessive Inheritance The recessive gene is located on an autosome Letters used are lower case (bb) Unaffected parents (heterozygous) can produce affected offspring (if they get both recessive genes ie homozygous) Inherited by both males and females Can skip generations If both parents have the trait (homozygous) then all offspring will also have the trait. E.g. cystic fibrosis, sickle cell anaemia, thalassemia

Sex (X) linked inheritance The Y chromosome is shorter than the X chromosome Males have no second copies of sex-linked genes. All of a male’s sex-linked genes are expressed.

Sex (X) Linked Inheritance

Sex linked inheritance Dominant Dominant gene on X chromosome Affected males pass to all daughters and none of their sons Genotype= XAY If the mother has an X- linked dominant trait and is homozygous (XAXA) all children will be affected If Mother heterozygous (XAXa) 50% chance of each child being affected E.g. dwarfism, rickets

Sex linked inheritance Dominant

Sex linked inheritance Dominant

Sex linked Inheritance Recessive Gene located on the X chromosome Males cannot be carriers (only have 1 X so either affected or not) More males than females affected (males inherit X from mother) Females can only inherit if the father is affected and mother is a carrier or affected An affected female will pass the trait to all her sons Daughters will be carriers if father is not affected Can skip generations E.g. colour blindness, haemophilia, Duchene muscular dystrophy

Sex linked Inheritance Recessive

Sex linked Inheritance Recessive

Hemophilia is a rare, inherited bleeding disorder in which your blood doesn’t clot normally. If you have hemophilia, you may bleed for a longer time than others after an injury. You also may bleed internally, especially in your knees, ankles, & elbows. This bleeding can damage your organs or tissues &, sometimes, be fatal.

Sex linked inheritance Recessive Genes are carried on the sex chromosomes (X or Y) Sex-linked notation XBXB normal female XBXb carrier female XbXb affected female XBY normal male XbY affected male

Sex linked recessive problem Red-green colour blindness in men is caused by the presence of a sex-linked recessive gene c, whose normal allele is C. a) Can two colour blind parents produce a normal son? b) Can they produce a normal daughter? c) Can two normal parents produce a colourblind son or daughter? d) Can a normal daughter have a colourblind father or mother? e) Can a colourblind daughter have a normal father or mother?

Mendel Discovered the Law of Segregation Organisms inherit two copies of each gene, one from each parent. The two copies segregate during gamete formation. The last two conclusions are called the law of segregation. purple white

General Pedigree

Autosomal Dominant Pedigree Look for: Trait in every generation Once leaves the pedigree does not return Every person with the trait must have a parent with the trait Males and females equally affected

Autosomal dominant pedigree

Autosomal Recessive Pedigree Look for: Skips in generation Unaffected parents can have affected children Affected person must be homozygous Males and females affected equally

Autosomal recessive

Sex linked recessive