1	Genetics: Traits & Genes
2	Learning Objectives Key Concepts: Trait (characteristics), genetic characteristics, environmental characteristics Skills: Recognize that traits can be genetic or environmental or both
3	Human Genetics: Variation in Humans We are all different. Some people are tall, some are short, some have long fingers, some have short fingers. We have different colored hair, different colored eyes, different colored skin. Some can roll their tongues, while others can’t even roll R’s the way Spanish native speakers can! Things which vary within a species are called characteristics. Skin color, eye color and height are just a few of the many characteristics that make each of us different and unique. Characteristics such as height, color of hair, size, ability to roll ones tongues etc. are also referred to as traits.
4	Human Genetics: Variation in Humans This football team shows a great deal of variation in many of the teams characteristics, for example height, weight, size and strength of calf muscles, skin, color, hair color , eye color, intelligence (!), size of feet, upper body strength, fitness, quality of vision
5	Genes VS. Environment There are two types of characteristics: Hereditary or genetic characteristics: these characteristics are passed on, or inherited, from the parents to the offspring. Environmental characteristics: environmental characteristics are characteristics which are affected by the environment in which we live and the lifestyle that we lead ( weight, fitness .....) Which of the football teams characteristics are genetic? Which are environmental? How many are determined by genetic and environmental factors?
6	Genetic or Environmental Many characteristics which are genetic are also influenced by environmental factors. An example is skin color. The color of Ian's skin is certainly inherited from his parents, but Sam’s skin color is also affected by exposure to sunlight. So skin color is both a genetic and an environmental characteristic. In the figure on the next slide, some of the football team characteristics have been arranged in a Venn diagram.
7	Genetic and Environmental Scientists are still trying to decide whether some characteristics such as sexuality ( e.g. homo / heterosexuality), weight, alcoholism are genetic or environmental. The chances are that such undecided characteristics will turn out to be both genetic and environmental. What we mean by genetic characteristic is that the characteristic is controlled by genes.
8	Learning Objective Key Concepts: Gene, gene pair, homozygous, heterozygous Dominant gene, recessive gene, dominant/recessive (pair), co-dominant (pair), genotype, phenotype, trait Skills: Recognize that genetic traits can be inherited from parents. Understand that traits are controlled by genes. Recognize genes are found in the nucleus of every cell Recognize that ** Genes occur in pairs ** Be able to identify offspring phenotype distribution for a particular trait given the genotype and phenotype of the parents
9	Genes Genes are found in the nucleus of every cell. Genes contain the information needed to control the development of different characteristics. Each characteristic is controlled by a pair of genes: one is passed on from your mother and the other is passed on from your father. You have two genes for each characteristic. Let’s look at the genes for eye color. There are different forms of the eye color gene. There is an eye color gene which will give you brown eyes, one that will give you blue eyes, one that will give you green eyes and so on.
10	Genotype & Phenotype Let’s use the symbol B for the brown eye gene and the symbol b for the blue eye gene. Your genotype refers to the pair of genes that you have. Your phenotype refers to your appearance. If you have two B genes, you will have brown eyes.
11	Genotype & Phenotype If you have two b genes, you will have blue eyes. Your genotype is bb Your phenotype is BLUE Again, you are homozygous for eye-color, because both of your eye-color genes are the same.
12	Dominant & Recessive Genes Will you have one blue eye and one brown eye? Or blue eyes or brown eyes or something in between? The brown eye gene B is stronger than the blue eye gene b.
13	Another Example Dimples are also controlled by a pair of dominant and recessive genes. If D = dimples present; d = dimples absent, then you may have one of the following pairs of genes, one coming from each parent: DD, Dd or dd. If your genotype were DD then you would have dimples. If your genotype were dd on the other hand you would not have dimples. And because these genes are a dominant/recessive pair, if you had Dd, you would still have dimples. Once again, because one gene is stronger than the other, having a pair with consisting of the strong and the weak gene will result in the person having the trait controlled by the dominant gene. Notice also that, if the appearance is one that is controlled by the stronger gene then we cannot determine the genotype.
14	Dominant & Recessive Genes Here are some examples of dominant and recessive characteristics:
15	Exercise The table below shows Mr. Big’s gene pairs (genotype) that he inherited from his parents for the traits listed above. Determine his phenotype for each trait.
16	Co-dominant Genes Some characteristics are controlled by genes which are neither strong nor weak but are equal in strength. These are called co-dominant genes. The gene which controls your hair type is controlled by co-dominant genes: The straight hair gene h and the curly hair gene H are equal in strength or co-dominant. A person with both genes Hh will have neither curly or straight hair but something which is a combination of both, let’s call it wavy hair.
17	Co-dominant Genes: Genotype & Phenotype A heterozygous pair of genes that are co-dominant results in a phenotype that is something in-between the two.
18	How do you inherit your genes from your parents? Remember that you have two genes for each characteristic. One gene comes from your mother and one gene comes from your father. Imagine that your father and mother are both Bb for eye color. Genes from your father and mother can combine in four different ways, producing offspring with different phenotypes. (Remember that B is the dominant brown eye gene and b is the recessive blue eye gene.)
19	Eye color of offspring Of the four possible variety of children: Three have brown eyes One has blue eyes
20	Another Example Imagine that a man has straight hair and a women has wavy hair. Remember always that genes come in pairs. the curly hair gene is given the symbol H. the straight hair gene is given the symbol h. these genes are equal strength (co-dominant): someone with both genes (genotype Hh) will have wavy hair. (a) What are the genotypes of the man and the woman? The man has straight hair, he must have two straight hair genes. His genotype will be hh. The woman has wavy hair, she must have a straight hair gene and a curly hair gene. (Genes controlling hair type are co-dominant.) Her genotype will be Hh.
21	Another Example (b) If the man and the woman decide to have a child, what is the chance that the child will have (i) straight hair? (ii) wavy hair? (iii) curly hair? To answer this question, you must construct a table similar to the one that appeared in one of the previous slides to find out all the different ways in which the genes can combine. Such squares in biology are called punnet squares.
22	Another example: Offspring Hair Type
23	Another example: Offspring Hair Type Now going back to the question… (b) If the man and the woman decide to have a child, what is the chance that the child will have (i) straight hair? (ii) wavy hair? (iii) curly hair? (i) Half the children would have straight hair, so the chances of having a child with straight hair is 1 in 2 or 50%. (ii) Half the children have wavy hair, so the chances of having a child with wavy hair is 1 in 2 or 50% (as well). (iii) No child will have curly hair. The chances of having a curly haired child therefore is zero.
24	Probability and Reality Here however is the more important observation. If indeed the pair had several children, the only thing we would be able to say with certainty is that no child will have curly hair. It could be that The split is 50-50 between children with straight hair and those with wavy hair, or The split is something other than 50-50, or They all have straight hair, or They all have wavy hair. It’s like with the split in the genders of children in a family—if a couple has several children, probability dictates that the split is 50-50.
25	Probability and Reality But a family could end up with 5 boys and no girls, or 5 girls and no boys or more boys than girls or vice versa. I am sure you know of families that have all boys and no girls or vice versa!!