Human Genetics Exploring the Human Genome

Human Chromosomes  Let’s Review: –A diploid human cell contains 46 chromosomes –A haploid gamete or sex cell has 23 chromosomes –Chromosomes are a condensed form of DNA that carries all of the genetic information that makes up that organism

Human Chromosomes  Scientists have been analyzing our DNA to see what makes us human  They take pictures of our DNA when it is condensed into the form of chromosomes  After that they group the 23 pairs into matched pairs  When chromosomes are arranged like this it is called karyotyping (karyotype)

Human Chromosomes  Of the 46 chromosomes that make up each of our cells two of them are sex chromosomes  It is our sex chromosomes that determine whether or not we are female or male –Two X chromosomes and we are female (XX) –One X and one Y and we are male (XY)

Sex determination XX Female XY Male X X XY XX Female XY Male XX Female XY Male

Human Chromosomes  The other 44 chromosomes are known as autosomal chromosomes or autosomes  This picture shows what type of cell? Sex cells or autosomal cells?

Human Traits  Humans inherit genes according to the principles that Mendel came up with  Both parents randomly assort their genes into their sex cells and the two sex cells are joined in fertilization  Some traits are shown in the phenotype of the offspring while other traits are masked until further generations

A Human Pedigree  A pedigree is a chart that shows how traits are passed from one generation to the next  Spheres or circles represent females while boxes or squares represent males

 A half-shaded circle or square represents a carrier, a heterozygous individual. Pedigrees illustrate inheritance

I II III IV Pedigrees illustrate inheritance  A horizontal line connecting a circle and a square indicates that the individuals are parents, and a vertical line connects parents with their offspring.

Pedigrees illustrate inheritance  Each horizontal row of circles and squares in a pedigree designates a generation, with the most recent generation shown at the bottom I II III IV

? Pedigrees illustrate inheritance  The generations are identified in sequence by Roman numerals, and each individual is given an Arabic number. I II III IV

A circle represents a female. A square represents a male. A horizontal line connecting a male and female represents a marriage. A vertical line and a bracket connect the parents to their children. A half-shaded circle or square indicates that a person is a carrier of the trait. A completely shaded circle or square indicates that a person expresses the trait. A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait. Some regular DUDE. Section 14-1 A Pedigree

Human Traits  It can be quite difficult to trace an actual trait through generations of a family  Some believe that you receive your eyes from one parent and ears from another  Many traits, however, are considered polygenic ; Meaning: a trait that is controlled by many genes

Human Traits  The second reason that it is difficult to determine where you receive your physical characteristics from is because only some of your genes are controlled by inheritance  Many traits are strongly influenced by environmental, or non- genetic, factors –Nutrition and exercise –Habitat and lifestyle In arctic foxes temperature has an effect on the expression of coat color.

Human Blood Group Genes  Why is it important to know your blood type? –If you receive a transfusion of the wrong blood type there is a very strong chance that you will die –Each person has a specific blood type and can receive donor blood specific to the type of blood that pumps through their veins & arteries

Human Blood Group Genes  The ABO blood groups are the following: –Type A, Type B, Type AB, and Type O There are three alleles for the ABO blood groupThere are three alleles for the ABO blood group I A, I B, i I A, I B, i Phenotype (Blood Type) Genotype Antigen on Red Blood Cell Safe Transfusions ToFrom

Human Blood Group Genes  I A and I B are codominant  This means:  If you have both alleles you will have Type AB blood  If you have Type A or Type B with the i allele you will express the dominant trait of Type A or Type B Phenotype (Blood Type) Genotype Antigen on Red Blood Cell Safe Transfusions ToFrom

Type A Blood  Type A blood is the result of the genotype I A I A or I A i  The surface of all of the Type A blood molecules is the same throughout the body

Type B Blood  Type B blood is the result of I B I B or I B i  All of the blood in a Type B person has the same surface

Type AB Blood  The only way to have Type AB blood is to have the alleles I A I B  Because it has both surfaces it can accept donor blood from all blood types

Human Blood Group Genes  The i allele is recessive  This means:  If it is with any other allele it will be masked  If someone has both ii they will have Type O blood Phenotype (Blood Type) Genotype Antigen on Red Blood Cell Safe Transfusions ToFrom

Type O Blood  With two recessive alleles ii you have the Blood Type O  Type O blood has a smooth surface and because of that it is a universal donor

Human Blood Group Genes  Blood transfusions are specific  Type AB is the universal acceptor  Type AB can ONLY donate to another Type AB !!  Type O is the universal donor  Type O can ONLY accept another Type O blood type Phenotype (Blood Type) Genotype Antigen on Red Blood Cell Safe Transfusions ToFrom

Human Blood Group Genes  Human blood is governed by another gene as well  The Rh Blood group only has two alleles –Rh+ is dominant  Rh+ / Rh+ OR Rh+ / Rh- is positive –Rh- is recessive  ONLY Rh- / Rh- is a negative blood type

Human Blood Group Genes  When a doctor refers to your blood type he or she will use both groups  For example: you may have Type O negative blood

Autosomal Disorders  There are three types of autosomal disorders in humans: –Disorders caused by:  Recessive alleles  Dominant alleles  Codominant alleles

Recessive Autosomal Disorders  Albinism – is the lack of the pigment melanin in the skin, hair, and eyes  In this chart it shows that you must have both (aa) recessive alleles to be “albino”

Recessive Autosomal Disorders  People with PKU (phenylketonuria) lack the enzyme needed to break down phenylalanine  Phenylalanine is found in milk and many other foods  PKU is carried by a recessive allele found on chromosome 12

Simple Dominant Traits  A cleft chin, widow’s peak hairline, hitchhiker’s thumb, almond shaped eyes, thick lips, and the presence of hair on the middle section of your fingers all are examples of dominant traits.

Dominant Autosomal Disorders   Huntington’s disease  Huntington’s disease is a lethal genetic disorder caused by a rare dominant allele.  It results in a breakdown of certain areas of the brain.

Huntington’s disease  Ordinarily, a dominant allele with such severe effects would result in death before the affected individual could have children and pass the allele on to the next generation.  But because the onset of Huntington’s disease usually occurs between the ages of 30 and 50, an individual may already have had children before knowing whether he or she is affected.

Typical Pedigree of Huntington’s Disease I 1 II III

Incomplete Dominance Appearance of a third phenotype  When inheritance follows a pattern of dominance, heterozygous and homozygous dominant individuals both have the same phenotype.  When traits are inherited in an incomplete dominance pattern, however, the phenotype of heterozygous individuals is intermediate between those of the two homozygotes.

Incomplete Dominance  For example, if a homozygous red-flowered snapdragon plant (RR) is crossed with a homozygous white-flowered snapdragon plant (R′ R′), all of the F 1 offspring will have pink flowers.  The new phenotype occurs because the flowers contain enzymes that control pigment production.  The R allele codes for an enzyme that produces a red pigment. The R’ allele codes for a defective enzyme that makes no pigment.

Incomplete dominance: Appearance of a third phenotype Red White All pink Red (RR) White (R’R’) Pink (RR’) All pink flowers 1 red: 2 pink: 1 white

Incomplete dominance: Appearance of a third phenotype  Because the heterozygote has only one copy of the R allele, its flowers appear pink because they produce only half the amount of red pigment that red homozygote flowers produce.

Red White All pink Red (RR) White (R’R’) Pink (RR’) All pink flowers1 red: 2 pink: 1 white Because the heterozygote has only one copy of the R allele, its flowers appear pink because they produce only half the amount of red pigment that red homozygote flowers produce.

Human Genes & Chromosomes  Genes are located on chromosomes and each chromosome in the human genome is a different size  On each chromosome can be hundreds or even thousands of genes

Locating Genes Gene Sequence Stop signal Gene Start signal Promoter